NCERT CLASS 8TH MAIN PAGE

 

ENGLISH CLASS 8TH

ENGLISH CLASS 8TH NCERT

ENGLISH GRAMMAR CLASS 8TH

Science class 8th Ncert

      TOPIC :- MICRO-ORGANISMS FRIENDS & FOE        

 Microorganisms:  An organism that is too small to be seen by the unaided eye, especially a single celled organism, such as a bacterium is called microorganism. Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae. Viruses are also microscopic. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

Where do Microorganisms Live: They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.

Microorganisms and Us: Microorganisms play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases.

Commercial Use of Microorganisms: Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice and crushed fruit juices, etc.

Medicinal Use of Microorganisms: Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases.

Vaccine: When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

Increasing Soil Fertility: Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Commensals: Some microorganisms live inside our body. They help in certain functions of our body systems. For example some bacteria in our gastrointestinal tract help in digestion. These type of organisms which reside in our body and are beneficial as well are called commensals. Apart from them certain food like curd, contain beneficial bacteria.

 

Harmful Microorganisms: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.

Disease— causing Microorganisms in Humans: Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

There are some insects and animals which act as carriers of disease causing microbes. Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. Another example of a carrier is the female Anopheles mosquito, which carries the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus.

Some Common Human Diseases caused by Microorganisms

                

Disease— causing Microorganisms in Animals: Several microorganisms not only cause diseases in humans and plants, but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.

Disease— causing Microorganisms in Plants: Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.

 

Food Poisoning: Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.

Food Preservation: Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and changed colour. Common methods to preserve food in our homes are

i.       Chemical Method: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.

ii.     Preservation by Common Salt: Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.

iii.  Preservation by Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.

iv.   Preservation by Oil and Vinegar: Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

v.     Heat and Cold Treatments: You must have observed your mother boiling milk before it is stored or used. Boiling kills many microorganisms.

Similarly, we keep our food in the refrigerator. Low temperature inhibits the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Storage and Packing: These days dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Nitrogen Fixation: Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses). Sometimes nitrogen gets fixed through the action of lightning. But the amount of nitrogen in the atmosphere remains constant.

Nitrogen cycle: Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilized by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds.

When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

                                                    TEXTUAL QUESTIONS

Q NO 1:-  Fill in the blanks…

a. Micro Organisms can be seen with the help of a Microscope.

b. Blue green algae fix Nitrogen directly from air to enhance fertility of soil.

c. Alcohol is produced with the help of Yeast.

d. Cholera is caused by Bacteria.

Q NO 2:-Tick the correct answer.

a. Yeast is used in the production of alcohol.

b. The following is an antibiotic streptomycin.

c. Carrier of malaria –causing protozoan is  female anopheles mosquito’s.

d. The most common carrier of communicable diseases is housefly.

e. The bread or idli dough rises because of growth of yeast cells.

f. The process of conversion of sugar into alcohol is called fermentation.

Q NO 3:-Match the organisms in column-I with their action in column-II

Column-I Column-II

1. Bacteria                                                    causing cholera

2. Rhizobium                                               fixing nitrogen

3.Lactobacilli                                               setting of curd

4. Yeast                                                         baking of bread

5. A protozoan                                            causing malaria

6. A virus                                                      causing aids.

Q NO 4:-Can micro-organisms be seen with the naked eye? If not, how can they be seen?

ANS:- No, micro-organisms cannot be seen with naked eye because they are too small so we can only see them under microscope.

Q NO 5:-What are the major groups of micro-organisms?

ANS:- Micro-organisms are classified into four major groups based on their size. These groups are bacteria, fungi, protozoa and some algae. Viruses are different from other micro-organisms.

Q NO 6:-Name the micro-organisms which can fix atmospheric nitrogen in soil.

ANS:- Rhizobium bacteria and Blue green algae can fix atmospheric nitrogen in the soil.

Q NO 7:-Write ten lines on the usefulness of micro-organisms in our lives.

ANS:- Micro-organisms are very useful to us. They help us in the following ways.

1. Micro-organisms prepare manures by decomposing dead bodies of plants & animals.

2. They work as natural cleaner as they decompose the dead bodies of plants & animals.

3. These are useful in formation of many medicines.

4. They are also used as preservatives for food items.

5. Micro-organisms are used to produce alcohol at large scale.

6. Micro-organisms are used to prepare vaccines for various diseases.

7. Some of these are useful in production of fuel like methane.

8. Some of the micro-organisms are highly useful in preparation of Bio-gas.

9. Micro-organisms help us in food sector. They are used for curdling of milk. Preparation of bread and cake etc.

10. Micro-organisms also help in increasing soil fertility by nitrogen fixation.

Q NO 8:-Write a short paragraph on the harms caused by micro-organisms?

ANS:- Micro organisms are both “friends & foe” as these can be useful as well as harmful. There are some microbes which cause diseases both in animals as well as in plants like cholera by Bacterium called vibrio-cholera, T.B by Mycobacterium and some microbes like viruses even cause incurable diseases like Aids, Polio etc. Even there are some microbes which spoil our food stuffs and thus may cause food poisoning.

Q NO 9:-What are antibiotics? What precautions must be taken while taking antibiotics?

ANS:- Antibiotics are the group of useful micro-organisms which are used to make medicines that kill or stop the growth of disease causing microbes. For example Streptomycin, Tetracycline and Erythromycin etc. Antibiotics were discovered by “Alexander Fleming” in 1929.     

       Antibiotics should be taken on the advice of a qualified doctor. We should take proper dose of medicines as the excess or fewer doses can cause other complications and even the delicate organs of the body can be damaged. 

TOPIC :- COAL & PETROLEUM   

Resources: A resource is any means of supplying a material held in reserve which can be transformed into more valuable and useful item. Natural resources are those living or non-living substances available in the normal environment which are being exploited for supporting life and meeting human requirements. Resources are of two types; Natural and manmade resources. Natural resources are directly obtained from the nature i.e. forest, wildlife, minerals, air, water, solar energy, etc. Manmade resources are manufactured or synthesized by man, i.e. plastic, fertilizers, pesticides etc.

Types of natural resources: The important types of natural resources are

•        Inexhaustible Natural Resources: Resources that are unlimited in nature and are not likely to be exhausted by human activities fall under this category. Solar radiation, air, water, precipitation (rainfall, snow fall, etc.,) and atomic power are some instances of such resources. Some of them may undergo temporary imbalances due to human activity e.g. the quality of atmosphere due to air pollution.

•        Exhaustible natural resources: Natural resources that are limited in nature and are liable to be degraded in quantity and quality by human activities are exhaustible natural resources. Examples are forests, soil, wild animals, minerals, fossil fuels etc.

•        Renewable natural resources: The resources which can maintain themselves by natural recycling and reproduction or can be replenished if managed wisely. They include forests, crops, domestic animals, wildlife, ground water etc. they can last indefinitely and are not likely to be exhausted if a judicious balance is maintained between exploitation and replenishment.

•        Non-renewable resources: those resources which get exhausted with use because they cannot be recycled or replenished. They include metallic minerals and fossil fuels (coal, natural gas and minerals). In nature, these resources take several thousand years for their formation but the consumption of these resources by man is very fast.

 

Fuels:  The materials which are burnt to produce heat energy are known as fuels. Examples of fuels are wood, Coal, Domestic gas (LPG), Kerosene, Diesel and Petrol. Fuels are the concentrated store house of energy which is released in the form of heat when the fuels are burnt. Most of the fuels are carbon compounds with hydrogen. Fuels are classified as solid, liquid and gaseous fuels.

Fossil fuels: Those fuels which were formed by the decomposition of the remains of the prehistoric plants and animals (fossils) buried under the earth millions of years ago are known as fossil fuels. Examples of fossil fuels are coal, petroleum and natural gas.

Coal: Coal is a complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon.  Small amounts of nitrogen and sulphur compounds are also present in coal. It is found in deep coal mines under the surface of the earth. In India, coal is found mainly in Bihar, West Bengal, Orissa and Madhya Pradesh.

Formation of coal: Coal was formed by the decomposition of large land plants and trees buried under the earth millions of years ago. It is believed that millions of years ago, due to earthquakes and volcanoes etc. the forests were buries under the surface of the earth and covered with sand, clay and water. Due to high temperature and high pressure inside the earth, and in the absence of air, wood was converted into coal. The slow chemical process of the conversion of wood into coal under the surface of the earth is called as carbonization. It is a very slow process and may take thousands of years to take place.                                           The different types of coal are  Peat – 60% carbon, Lignite(soft coal) – 70% carbon, Bituminous (Household coal) – 80% carbon and Anthracite (Hard coal) – 90% carbon. The different varieties of coal differ in their carbon content, volatile matter and moisture.

Uses of coal:

•        It is used as fuel.

•        It is used in the manufacture of fuel gases like coal gas.

•        It is used in the manufacture of synthetic petrol and synthetic natural gas.

•        It is used as source of organic compounds like benzene, toluene, phenol, aniline, naphthalene and anthracene.

•        It is use to make coke.

Destructive distillation of coal:  The strong heating of coal in closed retorts in the absence of air is called destructive distillation of coal. The destructive distillation of coal provides us a large number of organic compounds and some inorganic compounds. The various products obtained by the destructive distillation of coal are coal gas, ammoniacal liquor (solution of ammonia), coal tar and coke.

•        Coal gas: Coal gas is a mixture of hydrogen, methane and carbon monoxide. All gases present coal gas can burn to produce heat, due to which coal gas is an excellent fuel having high calorific value. Coal gas is obtained by the destructive distillation of coal. That is coal gas is obtained by the strong heating of coal in the absence of air.  Coal gas was used for street lightening. It is used as a fuel in many industries situated near the coal fields.

•        Ammoniacal liquor: Ammoniacal liquor is a solution of ammonia gas in water. It is one of the by-product of the destructive distillation of coal. When the ammonia gas produced by the heating of coal in the absence of air is dissolved in water. It forms ammoniacal liquor. It is used to prepare fertilizers.

•        Coal tar: Coal tar is a thick liquid which is obtained during the destructive distillation of coal. It is a mixture of more than two hundred different carbon compounds and can be separated into many chemical substances by the process of fractional distillation, which are used to make drugs (medicine), dyes, explosives, paints, varnishes, plastics, synthetic fibers and pesticides. Bitumen, a petroleum product is used in place of coal tar for metalling the roads.

•        Coke: Coke is a tough, porous and black substance with 98% of carbon. It is prepared by heating coal in the absence of air, when coal loses all its volatile constituents and coke is left behind as a residue.

Uses of coke: some of the important uses of coke are

•                    It is used as a fuel.

•                    It is used for making fuel gases like water gas and producer gas.

•                    It is used as a reducing agent in metallurgy (like that o iron).

•                    It is used to prepare calcium chloride.

Petroleum: The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons missed with water, salt and earth particles. It is a mixture of compounds. Petroleum is lighter than water and insoluble in water. Petroleum is a natural product obtained from oil wells.

Formation of petroleum: Petroleum oil was formed by the decomposition of the remains of extremely small plants and animals (micro-organisms) buried under the sea millions of years ago. It is believed that millions of years ago, the microscopic plants and animals which lived in seas died and their bodies sank to the bottom of the sea and were soon covered with mud and sand, the chemical effects of pressure, heat and bacteria converted the remains  of microscopic plants and animals into petroleum oil.  This conversion took place in the absence of oxygen. The petroleum thus formed got trapped between two layers of impervious rocks (non porous rocks) forming an oil trap. In India petroleum is found in Assam, Gujarat, and Mumbai high and in the river basins of Godavari ad Krishna.

Refining of petroleum:

The process of separating crude petroleum oil into more useful fractions is called refining. The refining of petroleum is done by the process of fractional distillation. It is based on the fact that the different components of crude oil have different boiling point ranges. The fractional distillation of petroleum is done by using a tall fractioning tower or column.                                                                                                             The crude petroleum oil is heated to a temperature of about 400^oC in a furnace and the vapours thus formed are passed into a tall fractioning column from near its bottom. The fraction of petroleum having highest boiling point range is collected in the lowest part of the fractioning tower, whereas the fraction having lowest boiling point range is collected in the upper most part of the tower.  The various fractions obtained by the fractional distillation of crude petroleum oil are petroleum gas, gasoline or petrol, kerosene oil, diesel oil, fuel oil, lubricating oil, paraffin wax and Asphalt.

Petrochemicals: Petrochemicals are the organic compounds prepared from the hydrocarbons obtained from petroleum and natural gas. Some examples of petrochemicals are methyl alcohol, Ethyl Alcohol, ethylene, Butadiene, Benzene, toluene, D.D.T, and B.H.C.

Natural gas: Natural gas consists of mainly methane (CH₄), with small quantities of ethane ad propane. In fact, natural gas contains up to 95% methane, the remaining being ethane and propane. Natural gas occurs deep under the crust of the earth either alone or along with oil above the petroleum deposits. Natural gas is formed under the earth by the decomposition of vegetable matter. This decomposition is carried out by anaerobic bacteria in the absence of oxygen. Natural gas is stored under high pressure as compressed natural gas (CNG). Natural gas is a very important fossil Fuel. Natural gas is stored under high pressure

as compressed natural gas (CNG). CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes. Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilizers.

 

Q NO 1:- What are the advantages of using CNG & LPG as fuels?

Ans. Natural gas is a very important fossil fuel because it is easy to transport through pipes. Natural gas is stored under high pressure as compressed natural gas (CNG) .There are several advantages of using CNG & LPG as fuel.

1. CNG is used for power generation.

2. CNG is used directly for burning in homes and factories where it can be supplied through pipes Example as in Delhi & Gujarat.

3. Now being used as a non-polluting fuel for transport vehicles.

4. LPG does not produce any poisonous gases on burning.

5. LPG is easy to handle & convenient to store.

6. CNG & LPG are less polluting than other natural resources.

7. It undergoes complete combustion.

8. Less transportation cost.

 

Q NO 2:-Name the petroleum product which is used for surfacing of roads?

Ans. Coal tar is used for surfacing of roads but nowadays, Bitumen a petroleum product is used for metalling the roads in place of coal tar.

 

Q NO 3:-Describe how coal is formed from dead vegetation. what is that process called?

Ans. Millions of years ago, dense forests got buried under the soil due to natural processes like storms, floods & earthquakes. These got compressed as more & more soil got deposited over them. When they got buried deep in the soil, they were exposed to very high pressure & temperature. Under these conditions, these slowly got converted into coal. This process of formation of coal from dead vegetation is called carbonization.

 

Q NO 4:-Fill in the blanks.

1. Fossil fuels are Coal, petroleum natural gas.

2. Process of separation of different constituents from petroleum is called Refining of petroleum.

3. Least polluting fuel for vehicles is Compressed natural gas(CNG).

 

Q NO 5:-Tick true/false against the following statements.

1. Fossil fuels can be made in the laboratory. False

2. CNG is more polluting fuel than petrol. False

3. Coke is almost pure form of carbon. True

4. Coal tar is a mixture of various substances. True

5. Kerosene is not a fossil fuel. False

Q NO 6.Explain why fossil fuels are exhaustible natural resources?

Ans. Fossil fuels are exhaustible natural resources because the amount of these resources in nature is limited. They can be exhausted by human activities. Examples of these resources are forests, wild life, minerals, coal, petroleum, natural gas etc.

Q NO 7.Describe characteristics & uses of coke?

Ans. Coke is a tough, porous & black substance. It is almost pure form of carbon. It is obtained from the destructive distillation of coal. When coal is heated in a closed tube in the absence of air. It forms a solid residue called coke. Coke is used in the manufacture of steel & in the extraction of many metals.

 

Q NO 8.Explain the process of formation of petroleum?

Ans. Petroleum is believed to be formed from organisms living in the sea. As these organisms died, their dead bodies got settled at the bottom of the sea & got covered with layers of sand & clay. Over millions of years, the dead organisms were transformed into petroleum oil & other natural gas & other fossil fuels under the conditions of the absence of the air, high temperature & high pressure.

 

Q NO 9.What are exhaustible natural resources? Give an example.

Ans. The natural resources which are available to the human beings in limited quantity & are likely to be exhausted by various human activities in the near future are called exhaustible natural resources. Forests, wildlife, all kinds of minerals such as coal, petroleum & natural gas are exhaustible natural resources.

 

Q NO 10.What are inexhaustible natural resources? Give example.

Ans. The natural resources which are available to human beings in unlimited quantity & are not likely to be exhausted by various human activities are called inexhaustible natural resources. Air, water, soil & sunlight are inexhaustible natural resources.

 

Q NO 11.Why is natural gas called a clean fuel?

Ans.  1. Natural gas is called a clean fuel because the natural gas burns cleaner than the other fossil fuels such as coal & oil due to highly efficient combustion process which produces very few by-products that are released into the atmosphere as pollutants.

2. Natural gas produces 70% less carbon dioxide emissions compared to other fossil fuels.

3. Due to clean burning process natural gas does not leave residues like soot or ash when compared to coal.

4. Natural gas is non-toxic & is not poisonous to humans if inhaled in small volumes.

 

Q NO 12.What are the uses of coal?

Ans. Coal is one of the fuel used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also used in thermal power plants to produce electricity. Coal is used as a fuel in various industries.

    

CLASS 8^Th                                                                                                                                                                                        PREPARED BY:- DR.DAVOOD AHMAD MIR.

CONSERVATION OF PLANTS & ANIMALS

                                                                                 (SCIENCE)

Resources:- A resource is any means of supplying a material held in reserve which can be transformed into more valuable and useful item. Natural resources are those living or non living substances available in the normal environment which are being exploited for supporting life and meeting human requirements. Resources are of two types; Natural and manmade resources.

Natural resources:- Natural resources are directly obtained from the nature i.e. forest, wildlife, minerals, air, water, solar energy, etc.

Artificial resources: Manmade or artificial resources are manufactured or synthesized by man, i.e. plastic, fertilizers, pesticides etc. 

Deforestation: The destruction, reduction or removal of forest cover is known as deforestation. It may lead to the destruction of biotic potential of land or desert formation. The main reasons of the deforestation are

i.        The indiscriminate felling of trees for the purpose of timber, fuel and industrial demand of wood.

ii.      Overgrazing by a large livestock population.

iii.    Shifting cultivation for agriculture.

iv.    Construction of dams, reservoirs, canals, hydroelectric projects, roads and railways.

v.      Forest fires which can be natural or manmade.

Consequences of deforestation: The various effects of the deforestation are

i.        Large scale deforestation has badly affected the weather of the surrounding places.

ii.      It has lead to the scarcity of timber wood, fuel wood and the wood used in industries.

iii.    It has lead to soil erosion, droughts, floods and landslides.

iv.    Deforestation by overgrazing has reduced the regenerative capacity of the forests.

Biodiversity:- Biodiversity is the variability of all living organisms -- including animal and plant species -- of the genes of all these organisms, and of the terrestrial, aquatic and marine ecosystems of which they are part. Biodiversity makes up the structure of the ecosystems and habitats that support essential living resources, including wildlife, fisheries and forests. It helps provide for basic human needs such as food, shelter, and medicine. It composes ecosystems that maintain oxygen in the air, enrich the soil, purify the water, protect against flood and storm damage and regulate climate. Biodiversity also has recreational, cultural, spiritual and aesthetic values.

Biosphere reserves: Biosphere reserves are the large areas of protected land for conservation of wild life, plant and animal resources and traditional life of tribals living in the area. These areas are meant for conservation of biodiversity.

A biosphere reserve is an area of land or water that is protected by law in order to support the conservation of ecosystems, as well as the sustainability of mankind’s impact on the environment. This means that each biosphere reserve aims to help scientists and the environmental community figure out how to protect the world’s plant and animal species while dealing with a growing population and its resource needs.

Forest conservation: The conservation of forests is development, management and full protection of existing forest cover so as to provide optimum sustainable yield. The various measures to be taken for the forest conservation are afforestation, Conservation of reserve forests, Social forestry, Agro forestry, Urban forestry etc.

Wildlife conservation: Conservation of wild life is the management of wild flora and fauna in order to save them from their extinction as well as to get sustainable benefit for both present and the future. Some of the ways for the wildlife conservation are protection of natural habitats, maintenance of wildlife in protected areas, Protection through legislation etc.

Flora and Fauna: Flora and fauna refer to plant and wildlife, respectively. The indigenous plant and wildlife of a geographical region is often referred to as that region’s flora and fauna. Both are collective terms, referring to groups of plant or wildlife specific to a region or a time period.

Flora can refer to a group of plants, a disquisition of a group of plants, as well as to bacteria. Flora is the root of the word floral, which means pertaining to flowers. Fauna can refer to the animal life or classification of animals of a certain region, time period.

The flora and fauna of any given region is usually explained in biological terms to include the genus and species of plant and animal life, their preferred growing or breeding habits, and their connection to one another in the environment as well.

Endemic species: An endemic species is an animal or plant species whose habitat is restricted to a particular area or space on the globe. This general term is used for a range of creatures including mammal species, reptile species, bird species and insect species. Generally, an endemic species is a focus point for helping to protect biodiversity in a given environment.

Wildlife sanctuary: A wildlife sanctuary is a space which is set aside exclusively for the use of wild animals, who are protected when they roam or live in that area. Wildlife sanctuaries are also referred to as wildlife refuges in some areas. Typically, a wildlife sanctuary is created through a government mandate which sets the space aside for the use of animal protection, and rangers or other government employees may patrol the area to ensure that no one hunts or otherwise harasses the animals.

  Some of the wild life sancturies of  Jammu and kashmir are Dachigam, Surnisar-Mansar, Ramnagar, Overa. Jasrota, Nandni and trikuta wildlife sancturies.

National park: An area of a country that is protected by the government because of its natural beauty or because it has a special history. It the area preserved for wide life where they can freely use the habitats and natural resources without any intervention of human activities. These areas are large and diverse enough to protect whole sets ecosystem. They preserve flora and fauna, landscape and historic objects of an area.                       Some of the examples of national parks of India are satpura, Kishtwar high altitude national parks.

Red data book:- A Red Data Book contains lists of species whose continued existence is threatened. Species are classified into different categories of perceived risk. Each Red Data Book usually deals with a specific group of animals or plants (e. reptiles, insects, mosses). They are now being published in many different countries and provide useful information on the threat status of the species. 

Migration:- Migration refers to the movement of an organism or a group of organisms from its natural habitat to another place at a particular time every year. Organisms migrate from one place to another to avoid inhabitable climatic conditions or for breeding.

Reforestation or Afforestation:- Afforestation is the planting of trees to create a forest on non-forest land. It is different from reforestation, which is replanting trees where a forest has been depleted. The main purposes for implementing afforestation are commercial forestry and environmental restoration or preservation. 

                                                 Q NO 1:- Fill in the Blanks.                                                                                                                             (A)  A place where animals are protected in their natural habitat is called wild life sanctuary.                       (B)  Species found only in a particular area are known as endemic species.

(C) Migratory birds fly to faraway places because of climatic changes.

Q NO 2:- Differentiate between the following.

WILD LIFE SANTUARY	BIOSPHERE RESERVE
1. This is an area where wild animals        are protected and preserved. 2. Wild life sanctuary is a place found in      biosphere reserve. 3.Bori and Panchmarhi are two wild life     sanctuaries in Panchmarhi biosphere.	1.It helps to maintain the biodiversity        and culture of the area. 2.A biosphere reserve may also contain     other protected areas like wild life      sanctuary. 3.Panchmarhi for example is a        biosphere reserve.
ZOO	WILD LIFE SANTUARY
1.It is a place where we protect        animals. 2.Here artificial surroundings are    made for animals in place of natural        habitats. 3.Here animals are supplied prepared ‘     food.	1. Here too wild animals are protected         and preserved. 2.They live in their natural habitat.   3.They get their food from forests     (sanctuaries) themselves. The food is        fresh.
ENDANGERED  SPECIES	EXTINCT SPECIES
1.These are those species which are        facing the danger of extinction. 2.Tiger is an example of an endangered     species.	1.They are the species which have     already vanished from earth. 2. Dinosaur is an example of extinct      species.
FLORA	FAUNA
1.Flora are the plants found in a     particular area. 2. Sal, teak, mango, ferns are the     examples of flora.	1.Fauna are the animals found in a     particular region. 2.Blue –bull, barking deer, leopard,     Wild dog and wolf are the examples      of fauna.

Q NO 3:- Discuss the effects of deforestation on the following?                                                             (A) WILD ANIMALS:-Plants & animals are the habitat & food for wild animals. So cutting of trees      destroy the natural habitat of wild animals & they would become endangered species.                       (B) ENVIRONMENT:-Deforestation decreases the level of oxygen in the atmosphere. Rainfall &    fertility of soil will decrease due to deforestation. As a result there are increased chances of floods & drought.

(C) VILLAGES:-Most of the agriculture is done in rural areas when trees & plants are cut down, it leads to the change in soil properties.

(D) CITIES:-In cities there are more factories & automobiles. So deforestation will pollute the environment & hence the life in cities will not be healthy for living.

(E) EARTH:-Deforestation leads to increased floods & drought. Deforestation also leads to increase in temperature on earth causing global warming. Lesser trees mean more soil erosion.

(F) NEXT GENERATION:-Deforestation leads to the climatic changes which have a great effect on the next generation. The environment becomes polluted. So the next generation would not be as prosperous as previous one.

Q NO 4:-What will happen if:-

(A) We go on cutting trees:-If we go on cutting trees continuously, rainfall & the fertility of soil will decrease. Hence there are increased chances of natural calamities like floods & drought.

(B) If the habitat of an animal is disturbed:-Some of the species do not get appropriate food & shelter & with the passage of time they will come under the category of endangered species.

(C) If the top layer of soil is exposed:-The soil has less hums & becomes less fertile. Gradually the land converts into desert. It is called desertification.

Q NO 5:-Answer in brief:-

(A). Why should we conserve biodiversity?

ANS:-We should save our biodiversity so that we can conserve the wild life plants & animals which are necessary for an ecosystem. We all are interrelated & interdependent on each other so we have to conserve biodiversity to live a proper life.

(B).Protected forests are also not completely safe for wild animals. Why?

ANS:-People living in the neighbourhood encroach upon the animals & destroy them. Also if we cut down trees then animals will not have their habitat to live. Small insects will not be killed or eaten up by the wild animals & the ecosystem may get disturbed due to hunting of animals. So the forests are also not completely safe for wild animals.

(C).Some tribal’s depend on jungle. How?

ANS:- Some tribal’s depend on the jungle as the Forests provide them food items like seed grains,fruits,raw vegetables & other products like honey, fodder for their animals, wood fuel for heating & cooking even clothing using natural fibres,leaves & animal skins.

(D).What are the causes & consequences of deforestation?

ANS:- The main reason of deforestation & exploitation of forest resources is over utilization of resources by human beings to meet the ever growing requirements of an increasing population, rapid urbanization, industrialization. The consequences of deforestation will result in putting in danger the whole existence of human beings along with the biodiversity on the planet earth.

(E). What is Red Data Book?

ANS:- Red Data Book is the source book which keeps a record of all endangered animals & plants.

(F). What do you mean by the term Migration?

ANS:-Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.

Q NO 6:-In order to meet the ever-increasing demand in factories & for shelter, trees are being continuously cutted down. Is it justified to cut trees for such projects?

ANS:-It is not justified to cut down the trees at present rate for such projects. Trees are part of forests & forests are the most important part of our eco-system world-wide, reduced forest cover

have already started showing its devastating effects in terms of climatic changes. We must reduce our dependency on our forest resources to meet the ever increasing demand in factories & for shelter. We should look for some other alternatives for the same. We have to start reforestation at much larger scale taking it as a top priority.

Q NO 7:-How can you contribute to the maintenance of green wealth of your locality?

ANS:-

1. We can plant trees in open spaces, parks, along the sides of roads motivate others as well.

2. We can make use of roof water or water from kitchen for water harvesting to recharge the   

     ground water table.

3. We can recycle our organic waste from kitchen for making compost & use it in our kitchen  

     garden or plants.

4. We can reduce use of paper. we can save it, reuse used paper & recycle it.

Q NO 8:-Explain how deforestation leads to reduced rainfall?

ANS:- Deforestation increases the temperature & pollution level on the earth. It increases the level of carbon-dioxide in the atmosphere. As we know, plants need carbon-dioxide for photosynthesis. Fewer trees would mean that less carbon dioxide will be used up resulting in the increased amount of Carbon-dioxide  in the atmosphere. This will lead to global warming as carbon-dioxide traps the heat rays reflected by the earth. The increase in temperature on the earth disturbs the water cycle & may reduce rainfall.

Q NO 9:- DELETED

Q NO 10:-Why should paper be saved? Prepare a list of ways by which you can save paper?

ANS:- It takes 17 full grown trees to make one tonne of paper.Therefore,we should save paper. Paper can be recycled five to seven times for use. If each student saves at least one sheet of paper in a day, we can save many trees in a year. We should save, reuse used paper and recycle it. We can also save paper by using information technology for storage of printed data, books in digital form.

                             

                                            

                                                                                           

TOPIC:-  REPRODUCTION.   (SCIENCE)

                                                                                      

                                                                                                                                                                   

Reproduction:-  Reproduction is one of the most important and fundamental properties of living organisms by which every kind of living organisms multiplies to form new individuals of its own kind. In this process one generation of living organisms gives rise to the generation. It is a function essential for the life of the species. Reproduction is of two types. i.e. asexual and sexual reproduction.

i.        Asexual Reproduction: Asexual reproduction is the production of new individuals by mitotic divisions from a single parent. It does not involve the fusion of gametes, also called sex cells. There are many types of asexual reproduction, all producing individuals that are genetically identical to the parent.

ii.      Sexual reproduction: It is that type of reproduction which involves the formation of gametes from male and female parents and their fusion. It requires two individuals of opposite sexes. Male produces the male gamete called as sperm while as female produces female gametes called as ovum. In sexual reproduction the gametes are produced by meiosis in the gonad. Hence gametes have half the number of chromosomes as compared to the parents. Their fusion during fertilization restores the diploid number of chromosomes in the next generation.

Male reproductive system: The male reproductive system comprises of a pair of testes that are present in a thin-walled sac called the scrotum. The scrotum is contained within the abdominal cavity in the embryonic stage. Each testis is covered by a thick connective tissue layer. Internally, the testis is lobed. There are 15-20 lobes, each having a network of seminferous tubules and the interstitial cells between the tubules.  The seminiferous tubules produce sperms that are passed along the tubules to the posterior region of the testis. The sperms are produced by a process called the spermatogenesis. From the seminiferous tubules, the sperms are passed into a network of 10-12 ducts called the efferent ducts or the vasa efferentia. They are then passed into a highly coiled tubular part called the epididymis. The sperms from the epididymis pass into a distinct tube called the vas deferens, also called the sperm duct. Vas deferens is also coiled though not much. It rises into the abdominal cavity and loops over the ureter of that side. The passage that connects the testicular region with the abdomen is called the inguinal canal. Vas deferens is joined by the duct from the seminal vesicle to form the ejaculatory duct. The duct then passes through the Prostate glands and opens into the urethra. The system of tubules consisting of the vasa efferentia, epididymis, vas deferens, ejaculatory tube and the urethra is the duct system associated with the male reproductive system. Each sperm duct has the seminal vesicle of its side secreting a fluid into the common ejaculatory duct. This fluid along with the sperms is called the semen, a milky fluid.  Pair of small ovoid glands that secrete lubricating fluid into the urethra just before it enters the penis are known as Cowper’s glands. These glands help in the ejaculation of sperms. An external organ penis is a muscular organ containing erectile tissue. The tissue is richly supplied with blood vessels. On sexual stimulation the penis is gorged (supplied) excess with blood which causes it to become erect. During sexual intercourse, the penis is used for depositing the sperm in the vagina of females.

Female reproductive system: The female reproductive system consists of a pair of ovaries, a pair of oviducts, uterus, vagina and vulva. The main functions of the female reproductive system are to produce eggs, receive the sperms, and provide the site for fertilization, implantation of the growing embryo and development of the fetus.                                                                                                                                     From close to each ovary arises a tube like oviduct or fallopian tube, the free end of each fallopian tube is funnel shaped and bears finger like projections called fimbriac. Both fallopian tubes meet at the centre and forma broader triangular uterus. The lower end of uterus opens below into small tubular chamber called as vagina which opens out through an aperture called vulva. The excretory aperture is separated unlike males and lies just above the vulva.                                                                              

           Ovaries produce ova. The process of ovum producing from the ovary is called as ovulation. It starts at the age of 10 – 11 and continues up to the age of 45 – 59, while males produce sperms continuously throughout their life. On sexual maturation an ovum is produced every 28 days. This cyclic process is called ovarian cycle and is accompanied by menstrual cycle. It reaches the uterus and waits for sperm up to 16^th-17^th day of the cycle. If during this period ovum and sperm came in contact with each other. They fuse together to form a zygote. Otherwise ovum is degenerated and is eliminated from uterus. Zygote starts its development soon after its formation. It becomes multicellular and gets attached with the wall of uterus.

Fertilization: On reaching the stigma, the pollen grains put out a tube. This is called germination of the pollen grain. The tip of the tube contains the male nuclei. The tube grows and enters the ovule where it bursts at the tip releasing the male gametes. One of the male gametes fuses with the egg, the female gamete. The fusion of the male gamete with the female gamete is called fertilization. This results in the formation of zygote that is diploid. The zygote develops into the embryo. The other male gamete fuses with the polar nuclei. This result in the formation of a triploid nucleus called the endosperm nucleus. Since the process of fertilization involves two fusions, it is called double fertilization. The divisions of the endosperm nucleus result in the formation of the endosperm that nourishes the growing embryo. The ovule then becomes the seed and the ovary changes into fruit.

Process of formation of zygote:  A zygote is a single diploid cell, created through the merging of two haploid cells. After fertilization, the zygote starts to divide, laying the groundwork for the mature organism which will eventually be born, hatched, or grown. During fertilization process, the sperms are made in the tests of a man are introduced into the vagina of the women through the penis during copulation. During copulation millions of sperms are introduced into the vagina at one time. The sperms are highly active and mobile, which move up through the cervix into the uterus and pass into the fallopian tubes. One of the fallopian tubes contains an ovum which utilizes only one sperm for fertilization from a zygote which is referred as fertilization. Thus the fusion of a male gamete with female gamete to form zygote during sexual reproduction is called fertilization.

                The fertilization of ovum always takes place in the fallopian tube. The fertilization can occur only when copulation that is release of sperms takes place during the ovulatory period which is the middle of the menstrual cycle. If the ovum gets fertilized by a sperm the woman is said to be pregnant. When pregnancy begins the menstruation stops.

 

Test tube babies: The process of collecting freshly released egg and sperms and keeping them together for a few hours for IVP or in vitro fertilization (fertilization outside the body). In case the fertilization occurs, the zygote is allowed to develop for about a week and then it is placed in the mother’s uterus. Complete development takes place in the uterus and the baby is born like any other baby. Babies born through this technique are called as test-tube babies.

 

Development of Embryo: When the ovum is fertilized in the fallopian tube, zygote is formed which rapidly divides by mitosis and forms a hollow ball of hundred cells which is known as embryo for the development. The embryo then sinks into the uterus and gets embedded in its wall. The embedding of embryo into thick lining of uterus is known as implantation. After implantation a special tissue develops between walls of the uterus and the embryo which is known as placenta.

                With the help of the placenta, all the requirements for the development of foetus such as nutrition, respiration and excretion are derived from the mother’s body. The exchange of nutrients, oxygen and waste products takes place with the help of the placenta between the mother and the embryo. The umbilical cord joints the foetus to the placenta.      

                The time period between the fertilization and the birth of the baby is known as gestation. The average gestation period in human being is about 40 weeks or 280 days. During the gestation period the foetus grows to become a baby. The birth process begins when the strong muscles in the walls of the uterus contract.

 

Viviparous and oviparous animals: Animals are multicellular heterotrophic organisms living in different habitats. Animals include both invertebrates and vertebrate. Animals are oviparous or viviparous. Some animals are ovoviviparous. Oviparous animals lay eggs. Egg hatch into young ones. Viviparous animals give birth to young ones. Young ones of different animal species age called in different names.

 

 

Modes of Asexual Reproduction:

i.        Fission: Fission occurs in lower plants and animals such as the bacteria, blue-green algae and protozoa. In this process, the cell divides after the genetic material has divided. If the cell divides into two it is called binary fission. The DNA or the nucleus of a mature cell divides first and then the cell divides into two daughter cells of almost the same size. It is seen in bacteria and protozoans like amoeba and paramecium.                                                                                                   If the parent cell divides into many daughter cells, it is called multiple fission. It is seen in the life cycle of the protozoa, plasmodium (the malarial parasite). The nucleus divides many times and then the cytoplasm divides and surrounds the nuclei.

ii.      Budding: It is seen in certain fungi and multicellular animals. In budding, the parent cell or body gives out a lateral outgrowth called the bud. The nucleus divides and one of the daughter nuclei passes into the daughter cell. The bud grows in size while being attached to the parent body. It then gets separated from the parent by the formation of a wall. It then falls off and germinates into a new individual.   E.g. In case of hydra, the daughter hydra even develops hypostome and tentacles develop around the hypostome before being detached from the parent body.

Cloning:- Cloning is the asexual production of an exact copy of an original. So for example, one could use cloning to produce the exact copy of a single cell. The cell copy would be identical to the first cell and would have the same exact DNA sequence. In many cases, cloning has been used to reproduce type specific cells. In some instances, cloning of an individual organism, like the sheep, Dolly, has been possible.                               Unlike reproduction that involves two “parents,” such as a male and female plants, cloning has a single parent. This is often used in reproducing certain plants. Certain plants have undergone cloning processes for thousands of years, but they do not play a part in the ethical debates that surround cloning of animals, and most particularly humans.

Important definitions:

i.                    Unisexual: the organism that bears only one of the two sexes either male or female is called as unisexual.

ii.                  Bisexual or Hermaphrodite:  both types of sex organs are present in the same individual, that individual is known as bisexual or hermaphrodite. e.g. earthworm, hydra, tapeworm etc.

iii.                External fertilization: When fusion of gametes (sperm and ovum) takes place outside the body is called as external fertilization.

iv.                 Internal fertilization: If the fusion of male and female gametes takes place inside the body is called as internal fertilization.

 

 

 

 

 

 

 

 

                        TEXTUAL QUESTIONS

Q NO 1:-Explain the importance of reproduction in organisms?

ANS:- The life process like nutrition, respiration, excretion & circulation help an organism to remain alive. But all the organisms grow old and die. Thus reproduction is a process which is essential for the continuation of a species. It allows the organisms thus continuous ever after their death. In absence of reproduction, no organism would be left after their death and the species would perish.

Q NO 2:-Describe the process of fertilization in human beings?

ANS:-  Human beings show internal fertilization in which fertilization takes place inside the female body. The male & female gamete s fuse to form the structure called zygote and then zygote divides continuously and undergoes growth in size & forms embryo. This stage is called embryonic stage and ultimately results in the formation of a new individual.

Q NO 3:-Choose the most appropriate answer:

(a). Internal fertilization occurs:

      (i).In female body

      (ii).Outside female body

      (iii).In male body

      (iv).Outside male body.

ANS:- In female body.

(b). A tadpole develops into an adult frog by the process of:

      (i).Fertilization

      (ii).Metamorphosis

      (iii).Embedding

      (iv).Budding.

ANS:- Metamorphosis

(c). The number of nuclei present in a zygote is:

      (i).None

      (ii).One

      (iii).Two

      (iv).Four

ANS:-Two.

Q NO 4:-Indicate whether the following statements are true (T) or False (F).

      (a).F

      (b).T

      (c).T

    (d).F

    (e).T

    (f).F

    (g).F

    (h).T

    (i).T

    (j). F

Q NO 5:- Give two differences between a zygote and a foetus?

ZYGOTE	FOETUS
1.Zygote is formed by the fusion       of male and female gametes. 2.Zygote is made up of two cells    sperm and ovum.	1.Foetus is formed by repeated     divisions in zygote 2.Foetus is made up of cells and has      a complete shape and size.

ANS   
Q NO 6:-Define asexual reproduction. Describe two methods of asexual reproduction in animals?

ANS:- Asexual reproduction is that type of reproduction in which  production of new individuals from a single parent without the involvement of sex cells is called asexual reproduction. It does not involve the fusion of gametes or sex cells. There are many types of asexual reproduction. E.g Amoeba, Paramecium.

Q NO 7:-In which female reproductive organ does the embryo get embedded?

ANS:- The embryo get embedded to the wall of the uterus of female reproductive organ.

Q NO 8:-What is metamorphosis? Give examples:

ANS:- It is the process by which the young form of insects and some animals such as frogs develop into adult is in a very different form where earlier stage of development is in very different from adult stage. E.g: Frogs, Butterflies & Silk worms show metamorphosis.

Q NO 9:-Differentiate between Internal fertilization & External fertilization?

ANS:-

INTERNAL FERTILIZATION	EXTERNAL FERTILIZATION
1.In this type of fertilization the fusion of male and female gametes takes place inside the female body. E.g: Human beings, birds.	1. In this type of fertilization the fusion of male and female gametes takes place outside the female body. E.g: Fish, frogs.

 

         

                                

                          

TOPIC :-SOUND               

                                                                                                                  

Choose the correct Answer:-

Q NO 1:- Sound can travel through?

ANS:- Solids, liquids and gases.

Q NO 2:- Which of the following voices is likely to have minimum frequency?

ANS:-  A man.

Q NO 3:- In the following statements, tick T against those which are true, and F against those   

 which are false:

1.Sound cannot travel in vacuum. T

2.The number of oscillations per second of a vibrating object is called its time period. F

3.If the amplitude of vibration is large, sound is feeble. F

4. For human ears, the audible range is 20 HZ to 20,000 HZ. T

5.The lower the frequency of vibration, the higher is the pitch. F

6. Unwanted or unpleasant sound is termed as music. F

7. Noise pollution may cause partial hearing impairment. T

Q NO 4:- Fill in the blanks.

1.Time taken by an object to complete one oscillation is called time period.

2.Loudness is determined by the amplitude of vibration.

3.The unit of frequency is Hertz (HZ).

4.Unwanted sound is called noise.

5.Shrillness of a sound is determined by the frequency of vibration.

Q NO 5:- A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Sol:- No. of oscillations = 40

Time taken = 4 sec.

Time period =?

 Frequency =?

 We know, frequency = No. of oscillation

_______________

Time taken in sec.

F =40/4.=10 HZ.

Time period = 1/ f

                                    T=1/ 10 =0.1 sec.

Q NO 6:- The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Sol: Here frequency of wings =500 vibrations per second.

 = 500 HZ.

Time period =?                                                                                                                               

 We know, time period =1/f.

t =1/500

=0.002

=2/1000

=2 × 10-³Sec.

 

Q NO 7:- Identify the part which vibrates to produce sound in the following instrument.

1.DHOLAK:- Stretched membrane                                                                                          

2.STRING:-Stretched string

3.FLUTE:-Air column.

Q NO 8:-What is the difference between noise and music? Can music become noise sometimes?

ANS:-

NOISE	MUSIC
1.It is an unpleasant sound. 2.It causes discomfort. 3.It can lead to the health problems such as high blood pressure, heart attack and partial deafness.	1.It is a pleasant sound. 2.It has soothing effect. 3.No health problems are associated with it.

 

Yes, music can become noise when it is too loud and loudness is beyond 80db.

Q NO 9:- List sources of noise pollution in your surroundings?

ANS:- There are many sources of noise pollution in our surroundings.

1.Sound of vehicles and their horns. Explosions including bursting of crackers, high volume of   

    loudspeakers.

2.Television and transistor radio at high volumes, some kitchen appliances desert coolers, air  

    conditioners, all contribute to noise pollution.

Q NO 10:-Explain in what way noise pollution is harmful to humans.

ANS:-Presence of excessive noise may cause many health related problems to humans.

1.     Lack of sleep.

2.     Hypertension (high blood pressure)

3.     Anxiety and many more health disorders may be caused by noise pollution.

4.     A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Q NO 11:-Your parents are going to buy a house .They have been offered one on the roadside and other three lanes away from the road side. Which house would you suggest your parents should buy? Explain your answer.

ANS:-I would suggest my parents to buy a house which is three lanes away from the roadside, because the house situated on the roadside will have the following disadvantages in comparison to the house three lanes away from the road side.

1.     Lots of noise due to passing of vehicles.

2.     Smoke and dust produced due to traffic on roads.

3.     Sound of pressure horns at the time of traffic jams.

 

 

 

 

 

 

Q NO 12:-Sketch larynx and explain its functions in your own words.

ANS:-In humans, the sound is produced by the larynx also called voice box. At the upper end of the wind pipe there is larynx. There are two vocal cord stretched across the larynx leaving a narrow slit between them for the passage of air.

When the lungs force air through the slit, the cord begins to vibrate producing sound. The muscles close to the vocal cords become tighter or make the cords loose thus changing the quality of sound is produced.

Q NO 13:-Lightning and thundering take place in the sky at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain?

ANS:-Lightning and thundering takes place simultaneously in the sky but we can see light earlier than thunder is heard, because light travels faster i.e.(3×10⁸m/s) than sound i.e. (340m/s).So it reaches us before the sound does.

 FOOD PRODUCTION & MANAGEMENT

  

PREPARED BY:- DAVOOD SIR.

 CLASS 8^TH                                                                                         

Agriculture:-the word Agriculture is derived from the Latin word “ager” meaning field and “cultura” meaning cultivate. So agriculture means the cultivation of crops. Agriculture is defined as the  science of of raising food crops and other crops useful to man. It includes the preparation of land for growing the crop plants, besides the breeding and management of animals.The various practice included in the agriculture are: Preparation of soil (ploughing, leveling and manuring), sowing, application of fertilizers, irrigation, weeding, crop protection, harvesting, threshing, storage etc.

Crop plants: A crop is defined as the cultivated produce from the ground.i.e. any plant grown and cared for in a field for some output is generally known as crop plants or simply crop. All food items like grain, vegetables, fibers and fruits are corps. Crops are classified as cereal crops, fiber crops; pulses oil seeds, root crops, tuber crops, sugar crops, plantation crops etc. The main crops grown in the Jammu and Kashmir are Rice, wheat, Maize, Barley, Jawar & Bajra, Pulses, Sugar Cane, Oil seeds etc.

Horticulture:  Horticulture is the science or art of cultivating fruits, vegetables, flowers, or ornamental plants. Etymologically, "horticulture" can be broken down into two Latin words: hortus (garden) and cultus (tilling). The main horticultural crops include vegetables, fruits crops, decorative plants and flower crops.

Sylvanculture or silviculture: Sylvan means wood and trees: cultural means cultivate. So Sylvanculture or silviculture means the branch of agriculture which deals with the cultivation of woods and trees. e.g.Seasame, pines, Teakwood etc.

Basic Practices for crop production: The basic practices included in the crop production are                

1.      Preparation of Soil: The preparation of soil is the first step before growing a crop. It includes the process of loosening and turning of the soil which is called Tilling or Ploughing. This is done by using ploughs which are pulled by bulls. Tractor driven cultivators are also used to till the soil. Tilling of the soils is important for following reasons:-

i.        This allows the roots to penetrate deep into the soil.

ii.      This allows the root to breathe easily.

iii.    The loosened soil helps in the growth of earthworms and microbes which further turn and loosen the soil and also help in adding humus to it.

iv.     This process brings the nutrient rich soil to the top so that plants can use these nutrients.

2.      Sowing: Sowing is the most important part of the crop production in which seeds are implanted in the prepared soil. Before sowing clean, healthy, good-variety and high yield seeds are selected. They are then sowed in the fields. In the traditional method of sowing seeds, a long pipe is used which has a funnel at its one end and the other end pierce into the soil through which seeds are placed. Now-a-days a machine or a tool known as seed drill is also used for sowing with the help of tractors. A seed drill saves time &labour. While sowing the seeds care should be taken to maintain proper distance and depth between the seeds to prevent damage of the seeds caused by birds and also to prevent overcrowding of the plants.

3.      Manuring: Manuring is the process of application of manures in the fields. It is mainly done by driller or manual application.

Manure: Manures are the organic products, which are obtained by the processing of dead bodies of plants and animals. Dead bodies of plants and animals are dumped in pits. They get decomposed to become manure. Using manure not only improves the texture of the soil but also, improves the water holding capacity of the soil.

Fertilizers: Fertilizers are the chemicals which replenish the soil with all the nutrients. They are produced in the factories and are inorganic products. Every fertilizer is rich in a particular nutrient. Some examples of fertilizers are urea, ammonia sulphate, potash, NPR etc. They help in getting better and healthy yields. But, excessive use of these chemicals is also harmful.

4.      Irrigation: Watering the crops in the fields is called ‘irrigation’. Farmers supply water to their agricultural lands by using ground water or from a nearby reservoir. Irrigation is done at different intervals. Irrigation should be done in a way in which water does not get wasted. Different sources of irrigation are like- wells, tube-wells, ponds, rivers.

Types of irrigation systems:

1.      Dug wells and tube wells: These are used to supply water in crop fields. Tube wells are used to pump up the ground water and to release it in fields as per the requirement.

2.      Canals: Canalsare man-made water channel systems, which are used to deliver adequate water to the fields. Canals are connected with water reservoirs, or rivers to distribute water in the fields.

3.      River lift system: River water is directly drawn from the river and is supplied to irrigate fields closer to the river. This is because in some regions, canals are irregular and insufficient because of low water levels in the river.

4.      Tanks: These are small, water storage reservoirs. These are helpful in delivering water in smaller areas.

1.      Sprinklers: Sprinklers work like fountains. Long perpendicular pipes having rotating nozzles on the top are joined to the main pipe lines at regular distances. When water is supplied, it comes out of these rotating nozzles which sprinkle water in all directions. Limited outflow of water, controls wastage of water. This method is more suitable for uneven and sandy soil.

2.      Drip System: This system allows the water to flow drop by drop at the roots of the plants. It contains a main pipe which has further lateral pipes containing small nozzles for the outflow of the water. Nozzles are such placed that they throw water at the roots of the plants, which saves water from flowing around uselessly. This technique is best suited for watering fruit plants, gardens and trees where availability of water is poor.

5.      Weeding:  weeds are the unwanted plants growing along crops. They share the nutrients meant for plants and thus are harmful for crop. We can control weeds with the help of chemicals Weedicides. The removal of weeds is called weeding. They are either removed manually or by chemicals. Manually this can be done with the help of Trowel (Khurpi) or Harrow. Weedicides are sprayed in the fields to kill the unwanted plants. These weedicides do not affect the main crop. Weeds are removed or killed during their vegetative phase before flowering or bearing seeds.

6.      Crop protection: Crops are affected by pests and a large number of weeds in fields. Uncontrolled growth of weeds and pests reduce productivity. Also, after harvesting, the produce is still at danger of getting spoilt by various biotic and abiotic factors. Therefore, these factors must be controlled to prevent loss.

Scare crow: A scarecrow is, essentially, a dummy, though traditionally, a human figure (or mannequin) dressed in old clothes and placed in fields by farmers to discourage birds such as crows or sparrows from disturbing and feeding on recently cast seed and growing crops.

Protection from weeds and pests: Weeds are controlled by using certain chemicals called weedicides. These chemicals don’t cause any damage to the crop. Weedicides like 2,4-D are diluted in water and sprayed on fields using a sprayer. Pests are controlled by using the chemical called as pesticides. These are the chemicals which are used to kill the pests growing on the crops. They kill the eggs and larvae of the insects.

Biocides: The chemicals produced from living organisms to kill specific pestsonlyonly without harming any useful organisms in the field are known as biocides.

7.      Harvesting: The harvestingis the process of gathering mature crops from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper.

Threshing: When the crop is harvested, it is cut along with the stalks. They are then separated and the grains are removed. This process of separation of grains from the chaff is called ‘Threshing’. This whole process is carried out with a machine called ‘Combine’ which is in fact a combined harvester & thresher. Mechanically it can be done with the help of threshers and combine.

Winnowing: Farmers with small holdings of land do the separation of grain and chaff by winnowing. The grains are thrown from the height in the direction of air. The air carries away the lighter chaff or dried stems and leaves and the heavier grain drop down in the form of a heap. This whole process is called winnowing.

8.      Storage of grains: The produce, which is harvested, needs to be stored safely to prevent it from getting eaten by pests and rodents. Therefore, farmers employ a number of storage methods to protect their produce and prevent it from getting spoilt. Some of the methods used are.

i.     Farmers sun-dry their seeds before storing them to reduce moisture in them. This protects the grains from insect pests, bacteria, and fungi.

ii.   Farmers store grains in jute bags or metallic bins. Granaries and silos are used for large-scale storing of grains. This protects the grains from pests like insects and rodents.

iii.Dried neem leaves are also used for storing grains at home. On a larger-scale, certain chemicals are used to protect the grains from pests and micro-organisms.

Improvement of crops: The various methods used by farmers for the improvement of crops are:

1.      Hybridization: Hybridisation is the technique of introducing characters of two desirable plants into a single offspring (hybrid) by means of artificial pollination. This involves crossing of genetically dissimilar plants. Most of the hybrid varieties of cereals have been evolved by this type of hybridization. The hybrid varieties thus evolved give good yield, are resistant to disease, are of better quality and have higher nutritive value. Several disease, pest and drought resistant varieties of wheat, tomato, sugarcane have been evolved by this method. 

2.      Field Fallow: Sometimes continuous growing of crops makes the soil barren or infertile. It needs to be left uncultivated so that it can regain its nutrients and fertility. This process of leaving soil uncultivated for one crop season is called fallowing.

3.      Crop Rotation: If the same crop is grown in the field year after year, it will lead to the deficiency of certain minerals. It is due to this fact that the same crop requires same type of nutrients. To solve this problem farmers are encouraged to grow one pulse crop in – between two cereal crops in the field. So the method of successive cultivation of different crops in an orderly manner on the same fields, in contrast to a one-crop-system or to haphazard crop successions is known as crop rotation. For example, growing legumes as fodder in one season and wheat in the next season. The roots of legumes have so many nodules which contain nitrogen fixing bacteria. These convert free atmospheric nitrogen into nitrates and increase the fertility of the soil. (Replenishing of soil with nitrogen)

4.      Mixed cropping:- allows two or more crops to be sowed simultaneously in the same land. Wheat and gram, wheat and mustard, ground nut and sunflower etc. are some common examples of mixed cropping. In mixed cropping, crops are chosen in such a way that they require different amounts of minerals.

Characteristics of a good storage structure:

1) The roof should not be leaking, i.e. and angle of 45 and thick thatch are necessary, with sufficient eaves.

2) The structure should be raised from the ground, approximately 1m for granaries and 15 cm (6 inches) for 

platforms.

3) The structure should be ventilated but should be solid enough to contain either shelled maize kernels or

shelled maize in bags.

4) The structure should be cool but dry.

5) The structure should be easy to treat with insecticides and to inspect routinely.

6) The structure should be protected from access by rodents, e.g. rats.

7) The structure should be strong and near or in the dwelling house.

 

Animal husbandry: It is the science of managing animal livestock. It involves feeding, breeding, and controlling diseases in farm animals. Animal husbandry involves the rearing of animals like cattle, poultry, and fish to obtain desired products from them.

Cattle farming (Dairying): Many products like curd, cheese, butter etc. are produced in a dairy.A dairy farm rears cows and buffaloes, which provide milk, the primary material for all these products. In India, two different species of cattle are widely reared, Bosindicus (cow) and Bosbubalis (buffalo). The purpose of cattle farming is usually for the production of milk and labour in agricultural fields. Female dairy animals used to obtain milk are known as milch animals. The production of milk depends upon the lactation period. Male animals are engaged in agricultural fields for labour work like carting, irrigation, tilling etc. Cattle used for labour is called draught animal.

Poultry farming: Poultry farming involves large-scale rearing of poultry birds.Poultry farming is undertaken to meet an increased demand of eggs and chicken. It deals with the management of domestic fowl in order to improve the quality and productivity of egg and chicken. Improvement in poultry variety is achieved through the process of hybridization or cross breeding.

Disease and control in poultry: Poultry fowls suffer from a number of diseases caused by virus, bacteria, fungi, parasites and nutritional deficiencies. Some of the diseases are fowl cholera, salmonellosis, fowl fox and parasitic infestations like roundworm, tapeworm and threadworm. Appropriate vaccinations and other preventive measures can prevent loss of poultry during an outbreak of disease.

Fish farming (Pisciculture): Fish farming is the practice of raising fish population commercially. It involves the production of aquatic animals, which are of high economic value like prawns, fishes, lobsters, crabs, shrimps, mussels, oysters etc.

There are two ways of obtaining fishes:

• Capture fishing is the process of obtaining fishes from natural resources
• Culture fishery is the practice of farming fishes

Farming can be done in both fresh water (such as rivers, ponds etc.) and marine ecosystems. Some important dishes are Labeo, barbus, Tuna, Cod,  Hilsa, Sardine, Mackerel etc.

Apiculture: The practice of bee keeping is known as apiculture, and the bee farms are known as apiaries. Bee keeping industry has become an additional income generating activity among farmers as it requires low investment. Moreover, beehives can also be used as a source of wax. Bee wax is used in several medicinal preparations.

Two main products are:

(1). Honey- This is the most important product of apiculture. It is used as food as well in medicines. It is useful to a healthy as well as sick person of all ages, even the newly born, and can be taken without the consideration of time. It is also used in the preparation of cakes and biscuits, etc, and also taken with or without milk. It is a mild laxative, antiseptic and sedative and helps in the formation of hemoglobin in anemic patients. It prevents cough, cold and fever. It is used as blood purifier and is also recommended in severe heart attack and to cure diabetes. It also gives quick energy.

(2). Bees Wax-It is useful in the manufacture of cosmetics, face creams, paints, polishes, plastics works, ointments, carbon papers and many lubricants.                    

                              

                                                                        TEXTUAL QUESTIONS

Q NO 1:-Name various sources of food?

 ANS:- The various sources of food are crop plants, vegetables, fruits & animals etc.

Q NO 2:-What are the various sources of plant nutrients?

ANS:- Manures & fertilizers are the various sources of plant nutrients.

 

 

 

Q NO 3:- Differentiate between Farmyard manure and green manure?

FARM YARD MANURE	GREEN MANURE	COMPOST
It is the most valuable organic matter. Commonly applied to the soil. This usually consists of straw, leaves and other materials like excreta of cattle.	The practice of turning or ploughing of green plants into soil for the purpose of improving physical structure as well as soil fertility is called green manuring. Crops like cluster beans, cowpeas etc are grown as green manure.	It consists of all cattle shed wastes and all the available refuse.

 Q NO 4:- What are the advantages of sea manures?

 ANS:- All types of manure properly mixed together can be used as manure after rottering.

Q NO5:- Name the two fertilizers supplying nitrogen phosphate and potash?

ANS:- (i). Npk,           (ii).  Urea,       (iii).  Super phosphate

Q NO 6:- Name any two irrigation systems In India?

ANS:- Through canals and through wells and tanks.

Q NO 7:- What are weeds? How do they affect crops?

ANS:- Unwanted plants which grow in the field along with our crop plants are called weeds. They affect our crops by competing with them for nutrients, Sunlight and water.

Q NO 8:- Name any two insecticides?

ANS:- Malathion & Polythion

Q NO 9:- Name two harvest festivals?

ANS:- Pongal & Baiskhi

Q NO 10:- Name two main crops raised in India and mention time of harvesting?

ANS:- (I). Rice, harvested in September-October.

            (ii). Wheat, harvested in March-April.

Q NO 11:- Name a machine which is used for harvesting?

ANS:- Combine or Harvester.

Q NO 12:- Name the cereals grown in India?

ANS:- Rice, Wheat, Maize, Barley, Bajra, Jowar, Ragi are the cereals grown in India.

Q NO 13:- Differentiate between agriculture and horticulture?

AGRICULTURE	HORTICULTURE
1. The word agriculture is derived from latin words, ager=field & culture=cultivation. 2.It means the study of science which deals with the production of plants and animals useful to man. 3. It provides us with food, clothing & shelter etc.	1. It is derived from latin words Hortus=garden & culture=cultivation   2. Horticulture means garden cultivation.   3. Horticulture provides us fruits, decorative plants and flowers.

Q NO 14:- Why is soil ploughed?

ANS:- (i). Ploughing eliminates all types of weeds.

           (ii). It destroys harmfull insects.

           (iii). It makes the soil porus.

           (iv). Ploughing makes the soil soft, Clear & suitable for sowing.

Q NO 15:- Name the methods of sowing?

ANS:- Broadcasting & by seed drill.

Q NO 16:- Why do farmers raise seedlings in nursery?

ANS:- The seeds are sown are first sown in nursery bed under the great care of the farmer, so that they are not demaged and only after a certain stage they are transferred to main field.

Q NO 17:- What is plant breeding?

ANS:- Plant breeding is a technique, Which involves the cross breeding or hybridization between two varieties of plants to obtain a new, better & disease resistant variety.

Q NO 18:-How is plant breeding performed?

ANS:- The anther of one flower are removed before maturation. The pollen grains of other flower are sprinkled over the stigma of ist flower from which anthers were removed. This plant is then again cross bred and the process is repeated several times, producing an important improved variety, the new variety will be disease resistant. This is how plant breeding is performed.  

Q NO 19:- What is crop rotation & what are its advantages?

ANS:- It is the process of growing one type of crop after another type of crop in different seasons on the same land.

           The advantages of crop rotation are that it kills pathogen & it also increases the soil nutrients hence makes soil more fertile.

Q NO 20:-Name two leguminous crops?

ANS:- Pea  &  Ground nut.

Q NO 21:- What are the advantages  of mixed cropping?

ANS:- Advantages of mixed cropping are:-

          (i).Mixed cropping save time and labour.

          (ii).Mixed cropping helps the products & wastes of one to be utilized by 

               another crop.

 Q NO 22:-Name two crops which are grown together?

ANS:- Ground nut & Cotton are usually grown together.

Q N 23:-Define field fallow?

ANS:-Leaving & keeping the field as such & not cultivating any crop for one season is called field fallow.

Q NO 24:-Write the important features of a good storage structure?

ANS:- (I).It should be waterproof.

          (ii).It should protect the grains against variation in temperature & humidity.

          (iii).It should be easy to clean.

          (iv).It should be located at a place, where transportation becomes easy.

          (v).It should be well protected from rodents, rats etc.

          (vi).It should be convenient for regular checkup of stored food grains.

          (vii).It should be convenient for the use of pesticides.

Q NO 25:-What is live stock?

ANS:-All the domesticated & other animals useful to man constitute live stock.

Q NO 26:-Name any four poultry birds?

ANS:-Chicken, Turkey, Geese & Duck.

Q NO 27:-What is a broody hen?

ANS:- An egg laying bird is called broody hen.

 Q NO 28:-Name any breeds of :

                   (a). Cows     (b). Buffaloes.

ANS:- (a).Breeds of cows are: Red, Sindi, Shahwal & Gir.

           (b).Breeds of Buffaloes are: Murrah, Jaffarabadi & Mehsana.

Q NO 29:-Why is fishery flourishing in india on a large scale?

ANS:- Fishries is flourishing in india on a large scale than other countries thus generates huge revenue & lively hood to lacks of people.

    (i).Fish provides us proteins.

   (ii).Fish provides us oil, which is used for various purposes.

    (iii).Corals are used as decorative purposes.

Q NO 30:-Name any four fishes?

ANS:- Catla, Rohu, Tuna Cod & Hilsa.

Q NO 31:-Give any two uses of honey?

ANS:-  (i).Honey is easily digestable & Anticeptic.

            (ii).It contains Sugars, Water & Enzymes which are necessary for digestion.

Q NO 31:-Give any two uses of wax?

ANS:- (I).It is used in making candles.

           (ii).It is used for treatment of joint pains.

 Q NO 32:-Give any four points for care of animals?

ANS:-  (I). The animals should be given food regularly.

            (ii).The animals should be cleaned regularly.

            (iii).The sheds of animals should be cleaned regularly.

             (iv).Precautions should be taken against diseases related to animals.

Q NO 32:- Name the following?

(i).Five requirements essential for obtaining good crop production.

 ANS:-Five requirements essential for obtaining good crop productions are:

               (a).Right kind of soil.

               (b).Good quality of seeds.

               (c).Protection from weeds & pests.

               (d).Required amount of water.

               (e).Proper implements.

(ii).Two types of fertilizers.

ANS:- Urea  &  NPK fertilizer.

(iii).Some chemicals used to protect crops from insects pests and weeds.

ANS:-Malathion, Polythion, Dimecron &  2-4-dichlorophenoxy acetic acid.

(iv).Some animal products.

ANS:-Meat, Milk, Eggs, Honey, Silk, Wool & Wax.

(v). Members of a colony of bees.

ANS:-(a).Workers (sterile females)

          (b).Drones   (sterile males)

          (c).Queen    (fertile females)

Q NO 33:-Fill in the blanks?

(a).Trowel

(b).Plough

(c).June & july

(d).Paddy & vegetables

(e).March & April

(f).Transplanting

(g).Jewellary

(h).17%       &     78%

(i).Pens

(j).Buffaloes.

Q NO 34:-What is the process of turning & loosening the soil called?

ANS:-Ploughing.

Q NO 35:-Which implement is used for tilling soil?

ANS:-Ploughs.

Q NO 36:-Which implement is used for breaking the large  lumps of soil?

ANS:-Cold crushers

Q NO 37:-What is the implement used for sowing seeds?

ANS:- Seed drill.

Q NO 38:-What is the top part of the drill called?

ANS:- Seed bowl.

Q NO 39:-What is an egg laying bird called?

 ANS:-Broody hen.

Q NO 40:-Name the members of bee colony?

ANS:-Workers, Drones 7 Queen.

Q NO 41:-Which material is used to cower the floor of a hen house?

ANS:-Straw.

Q NO 42:-Which is the common food of poultry chicken?

ANS:-Grains.

Q NO 43:-Which bee is responsible for laying eggs?

ANS:-Queen bee.

Q NO 44:-Give the scientific reasons for the following?

 (i).Grains, pulses, vegetables & fruits should be used in our daily life?

ANS:-These form the constituents of the balanced diet for maintaining the well being of the human body.

(ii).The soil should be loosened before seeds are sown?

ANS:-Loosened soil is better ventilated and suitable for the growth of tiny plant living in it. It also allows roots to penetrate freely and deeper.

(iii).Seeds should be sown at a proper depth in the soil?

ANS:-Because if they are sown too deeper they will not be able to germinate and if they are sown at a shallow deep then birds will eat them easily.

(iv).Fruits and vegetables should be washed thoroughly  before eating?

ANS:-Because they have a coating of pesticides , Otherwise they are harmful for our body.

(v).Grains are dried thoroughly before they are stored?

ANS:-Because moisture and humidity promotes the growth of fungi on grains, which are harmful for our health.

                                          ANSWER THE FOLLOWING:-

Q NO 45:-What are the requirements of farming which would lead to  high yields of crops?

ANS:-The basic requirements which lead to high yield of crops are:

          (a). Right type of soil           (b).Use of manures       (c).Irrigation

          (d).Better varieties of seeds        

          (e).Use of chemicals which prevent the diseases of the plant crop.

Q NO 46:-what is tilling? How is it done?

ANS:-The process of loosening and turning the soil is called tilling or ploughing.

          It is done by an instrument called plough. The plough is dipped into the soil which turns the inner part of soil towards upper side and make the soil loosened.

Q NO 47:- Write a short note on the process of sowing?

ANS:-Sowing is the process of putting seeds in the soil. there are two methods of sowing of seeds. Broad casting  & seed drill

   Broad casting:-The sowing of seeds is done manually by spraying in the field is called broad casting.

  Seed drill:-Seeds are put into the bowl of the seed drill & when we pull the seed drill during its use the seeds from seed drill fell down into the ploughed soil.

Q NO 48:-What are manures? Discuss their important types?

ANS:- Manures are inorganic materials which supply the nutrients that a plant needs in small amount. The important types of manures are:

(a).Farm yard manure:- It is the most valuable organic matter ,commonly applied to the soil. This usually consists of remaining of straw, leaves & excreta of cattle.

(b).Green manure:-The practice of turning or ploughing of green plants into soil for the purpose of improving soil fertility is called green manuring.e.g Leguminous crops

Are grown as green manure.

(c).Compost:-It consists of all cattle shed wastes and all the available refuse.

Q NO 49:-What is a fertilizer? Explain its importance?

ANS:-Fertilizers are the chemical substances that are man made and are rich in Nitrogen, Phosphorus and  Potassium which are needed by the plants. E.g: NpK, Urea & Super phosphate.

      fertilizers are nutrients specific that is they are used mainly to increase the essential elements in the soil.

 Q NO 50:-What are broad casting and transplanting?

ANS:-Broad casting:- After the soil has been prepared, seeds of crop plants are sown in it. There are two methods of sowing them. Sowing by hand or by using seeds drill is called board casting.

Transplanting:- it is a process of taking out young plants from nursery beds and transferring them into main fields.

Q NO 51:-What is the difference between manure and fertilizer?

MANURE	FERTILIZER
1. These are organic substances prepared from the decomposition of plant and animal wastes. 2.They contain a mixture of various nutrients, recycled from biomass wastes 3.They are not easy to store or transport. 4. They are never harmful to the soil.	1. These are mixtures of chemical compounds rich in Nitrogen, Phosphorus & Potassium. 2.Chemical fertilizers are Nitrogenous,  Phosphate Potassium etc. 3.They are easy to store or transport.   4. They are harmful if used in excess.

ANS

 

 

 

 

 

 

 

 

Q NO 52:-Why are weeds harmful? What is used to remove them?

ANS:- Weeds are unwanted plants which grow in the field along with crop plants. They compete with the crop plants for nutrients, sunlight & water. Thus they reduce the crop yield.

Weeds can be removed by the following methods:

(a).Tilling:- The process of loosening and turning the soil by the use of Plough is called tilling. This process helps in uprooting and billing of weeds.

(b).Manual removal:-This method includes the physical removal of weeds by uprooting or cutting them close to the ground with the help of Khupra or Horrow.

(c).Chemical method:- In this method weeds are controlled by using some chemicals called weedicides like 2,4-D.

Q NO 53:- What are insecticides? Give examples.

ANS:-Insecticides are chemicals which kill the pests or harmful insects as well as their eggs and larvae, but don’t effect the plants. E.g Malathion, Dimecron & Polythion.

Q NO 54:-How do insecticides protect the crop?

ANS:-When we sprinkle insecticide to our crops to protect our crops from demaging by insects. so,insects are killed and crops are protected.

Q NO 55:-Which are the two main seasons in India for cultivating crops?

ANS:-The two main seasons in India for cultivating crops are:

(i). Rabi crop.        (Nov to April)

(ii).Kharif crops.  (June to October)

Q NO 56:- Name some harvest festivals in india?

ANS:- Baishakhi, Holy,  Diwali,  Pongal  & Bihu etc.

Q NO 57:-Name four factors responsible for improvement of a crop?

ANS:-Factors responsible for improvement of a crop are:

  (i). Plant breeding.                                  (ii). Soil improvement.

  (iii).Protection from pests & weeds.   (iv). Manuring and irrigation.

Q NO 58:-Write short note on the process of harvesting?

ANS:-Harvesting is a process in which the mature or ripe crop is cut. The harvested grains called produce represent crop yield. it is done using a sickle, even tractor driven machines are also used for harvesting the fruits and vegetables are plucked.

Q NO 59:-What do you understand by mixed cropping?

ANS:- Mixed cropping is the practice of cultivating two crops simultaneously is done to economise the time and energy, This is called mixed cropping.

Q NO 60:-Why are field some times allowed to remain fallow?

ANS:- Some fields are allowed to rest and regenerate for at least  a season to support a crop, this is known as field fallow. By this process growth of humus increases which promotes the growth of soil microorganisms, lead to a rich increase in nutrients.

Q NO 61:-List the importance of fish in our life?

ANS:-Fish is the major source of animal protein. The oil obtained from the fish can be used for various purposes.

Q NO 62:-What is the nutrient value of honey?

ANS:-Honey contains 17% water & 78% sugar with minerals and enzymes, which helps in digestion.

Q NO 63:-How are domesticated animals useful to us?

ANS:- Uses of domesticated animals are:

(i).These animals play an important role in the welfare of mankind.

(ii).They are used for our own work and food.

(iii).Domesticated dogs are used for our home protection.

………………………………………………………………………………………………………………………………….

      

TOPIC :- COMBUSTION & FLAME        

                                (SCIENCE)

 

Combustion: The burning of a substance in presence of oxygen of air in which heat and light are produced is known as combustion. Combustion is a highly exothermic process, so a lot of heat energy is released in combustion and flames can usually be seen. Carbon dioxide and water vapour are the usual products of combustion.

Conditions necessary for combustion: There are three conditions necessary for combustion to take place.

i.                    Presence of a combustible substance.

ii.                  Presence of a supporter of combustion like oxygen of air.

iii.                Heating of the combustible substance to its ignition temperature.

Combustible, non-combustible and inflammable substances:

i. The substances which can catch fire on heating to their ignition temperature in presence of air are known     as combustible substances. e.g. wood, paper, kerosene oil, straw, charcoal, matchsticks etc.

ii. The substances which cannot catch fire and does not burn are known as non-combustible substances. e.g.     iron nails, stone pieces, glass, steel etc.

iii. The substances which have very low ignition temperature and can catch fire with a flame are called             inflammable substances. e.g. petrol, alcohol, LPG, etc.

Ignition temperature: The lowest temperature at which a substance catches fire and starts burning is called   as its ignition temperature. A substance cannot catch fire or burn as long as its temperature is lower         than its ignition temperature.

Types of combustion:

i. Spontaneous combustion: A combustion reaction in which no external heat is given to start it is known as             spontaneous combustion. This type of combustion takes place itself at normal room temperature.          e.g. the burning of white phosphorus on its own, when exposed to air for some time.

ii. Rapid combustion: A combustion reaction in which a large amount of heat and light are evolved in a short             time is known as rapid combustion. e.g. the immediate burning of domestic cooking gas in a gas             burner to give heat and light is an example of rapid combustion.

Fire extinguisher: A fire extinguisher is a substance or chemical used to put out a fire by removing one or             more requirements essential for producing fire. e.g. The contact between air and fuel. Water is the m  ost commonly used fire extinguisher. Some other examples of fire extinguishers are carbon dioxide,            foam type extinguishers etc.

Water as a fire extinguisher: water is the most common fire extinguisher for ordinary fires. When water is thrown on a burning substance, it gets cooled below its ignition temperature and stops burning. The fires caused by burning of oil or by electricity cannot be extinguished by the use of water over them because water is heavier than oil. Oil fires can be controlled by the use of foam type extinguishers because it breaks the contact between oil and air. Electrical fire can be controlled by the use of carbon tetrachloride fire extinguisher, and it should not be used in the closed rooms because a highly poisonous gas phosgene may be produced.

 

Flame: A flame is a region where combustion (or burning) of gaseous substance takes place. All gases which undergo combustion, burn with a flame. But only those solid or liquid fuels which vaporize on being heated, burn with a flame. e.g. wax is a solid fuel and kerosene is a liquid fuel which vaporize on heating, so both of them burn with a flame.

 

Structure of a flame: There are three distinct zones in a flame.

1. The innermost zone which is a dark and coldest part of a flame.  It consists of hot vapour of combustible             material (wax).

2. The middle zone is a bright luminous zone. Fuel partially burns in this portion of the flame forming carbon             particles. The glow of these carbon particles makes this zone luminous.

3. There is a thin outer zone faintly bluish in colour. In this zone oxygen from atmospheric air mixes with the    fuel bringing about complete combustion. This outermost zone is non luminous and has the highest   temperature of around 1800^OC.

                              

                                                     Structure of a flame

 

Fuel: The material which is burnt to produce heat is known as fuel. e.g. wood, coal, domestic gas (LPG), kerosene, diesel and petrol. Most fuels are carbon compounds with hydrogen. When a fuel burns it combines with oxygen to form carbon dioxide and water vapour and a lot of energy (heat and light) is produced during this process.

 

Calorific value of fuels: It is defined as the amount of heat liberated in kilojoules (kj) or kcal by the complete combustion of 1 kg of fuel. The unit of calorific value of fuel is kilojoules/kg. it is also known as the heat value of a fuel. (calorific value of various fuels given on the book).

 

Characteristics of an ideal fuel: The parameters like calorific value and rate of combustion make one fuel better than the other. Some characteristics of an ideal fuel are:

i. It should have high calorific value.

ii. It should have proper ignition temperature.

iii. It should have moderate rate of combustion.

iv. It should have low content of non - volatile material.

v. It should be Ready availability.

vi. It should have low cost.

vii. It should have abundant availability.

viii. It should be easy to store and transport.

 

Disadvantages of burning fuels:

i. The hydrocarbons present in the fossil fuels, release greenhouse gases, such as methane, carbon dioxide etc. which are capable of damaging the ozone layer.

ii. Besides, other harmful gases such as carbon monoxide and sulphur dioxide are responsible for acid rain, which has brought disaster for the ecology.

iii. Fossil fuels have contributed in more than one way for global warming.

iv. The burning of fossil fuels produces poisonous gases which can lead respiratory diseases and even to             death.

 

Global warming: Global warming means the rise in the temperature of the atmosphere of the earth. It happens when greenhouse gases (carbon dioxide, water vapour, nitrous oxide, and methane) trap heat and light from the sun in the earth’s atmosphere, which increases the temperature. This hurts many people, animals, and plants. It may lead to melting of polar ice and in turn rise in sea level certain low lying areas may even be permanently submerged under water.

                                     TEXTUAL QUESTIONS

Q NO 1:-List conditions under which combustion can take place?

ANS:-  The various conditions necessary for combustion are:-

1. Presence of combustible substance.
2. Presence of supporter of combustion.
3. Attainment of ignition temperature.

 

Q NO 2:-Fill up the blanks:-

ANS:-(a) Burning of wood and coal causes of air  pollution.

          (b) A liquid fuel, used in homes is kerosene. 

          (c) Fuel must be heated to its ignition temperature before it starts burning.

          (d) Fire produced by oil cannot be controlled by water.

                                                                                                                   

Q NO 3:-Explain how the use of CNG in automobiles has reduced pollution in cities?

ANS:-CNG is a clean gaseous fuel. It burns completely in air and does not produce any harmful gases. So , pollution is reduced in our cities by the use of CNG in automobiles.

Q NO 4:-Compare LPG and wood as fuel?

ANS:-LPG is a clean fuel. It is liquefied petroleum gas and is filled in cylinders. It burns with a blue flame and leaves no residue behind. Its calorific value is high. While as wood is not a clean fuel. When it burns it releases lots of smoke, and ashes are left behind. It gives very low amount of heat.

Q NO 5:-Give reasons:

a)        Water is not used to control fires involving electrical equipments?

ANS:-The substances used for extinguishing fires on electrical appliances or circuit should not be good conductors of electricity as there are chances of electro- conduction. So , water being a good conductor of electricity is not used for extinguishing fires on electrical appliances or circuit. Carbon tetra chloride is used for this purpose.

 

b)       LPG is a better domestic fuel than wood?

ANS:-LPG is liquefied petroleum gas. It has high calorific value of 55000 kj/kg. It burns with a smokeless flame and does not produce poisonous gases. While wood has less calorific value of 17000 -22000 kj/kg. Moreover it gives out smoke and poisonous gases on burning. So LPG is better domestic fuel than wood .

 

c)        Paper itself catches fire easily while as a piece of paper wrapped around an aluminium pipe does not?

ANS:-When a paper wrapped around an aluminium pipe is brought near a flame ,it does not burn because the heat gets transferred to aluminium pipe and the ignition temperature of paper is not achieved.

 

Q NO 6:-Make a labelled diagram of a candle flame?

ANS:-(Refer to book page no. 86 fig. 7.10).

 

Q NO 7:-Name the unit in which the calorific value of a fuel is expressed?

ANS:-Kilojoules per kilogram(kj/kg).

Q NO 8:-Explain how CO₂ is able to control fires? 

ANS:-CO₂  gas is heavier than air . So it forms an envelope around the burning fire. This cuts off the supply of oxygen gas and fire stops burning and gets in control.

Q NO 9:-It is difficult to burn a heap of green leaves but dry leaves catch fire easily .Explain

ANS:-Green leaves have a high moisture content in them and in heap of green leaves, oxygen present is very less where as dry leaves have no moisture content and there is lot of oxygen available in this heap. So it is difficult to burn a heap of green leaves

Q NO 10:-Which zone of flame does a gold smith use for melting gold and silver and why?

ANS:-Gold smith usually uses the uppermost, non-luminous blue flame for melting gold and silver because it is the hottest part of  the flame.

 

Q NO 11:-In an experiment 4.5 kg of a fuel was completely burnt . The heat produced was measured to be 180000kj.Calculate the calorific value of the fuel.

ANS:-Mass of fuel = 4.5 kg

   Heat produced = 180000kj

      Now, calorific value of a substance =     heat produced

                                                                               mass of fuel

                                                                     =     180000 kj

                                                                               4.5 kg

                                                                     =    40000 kj/kg.

 

Q NO 12:-Can the process of rusting be called combustion? Discuss.

ANS:-Rusting:- When iron is exposed to moist air, it gets coated with hydrated iron oxide. This process is called rusting and the coating formed is called rust. Chemically rust is hydrated form of ferric oxide, Fe₂O₃ .x H₂O. It is reddish brown in colour.

 The overall reaction for rusting is :-

             2Fe + O₂ + H₂O                                                   Fe₂O₃   +  H₂

                   _{(Iron)    (Oxygen)  (Water)                                                                       (Iron oxide)}       

                      

We know combustion is an oxidation reaction and rusting is also an oxidation reaction but very slow. So, rusting can be termed as slow combustion reaction.

Q NO 13:-Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose   water will get heated in a shorter time.

ANS:-Ramesh’s beaker will get heated in a shorter time because the outermost part of flame is the hottest part.

Q NO 14:-What is combustion?

ANS:-A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

 Q NO 15:-Name some combustible substances?

ANS:-Some combustible substances are wood, paper, kerosene oil, charcoal, petrol etc.

Q NO 16:-What are the different types of combustion?

ANS:-The different types of combustion are:-           

1.      Rapid Combustion:- The combustion reaction in which a large amount of heat and light is  produced in a short time is called rapid combustion.

    The burning of kerosene oil in a kerosene stove and the burning of wax in   

    a candle are some examples of rapid combustion.

2.      Spontaneous Combustion:- The combustion reaction which occurs on its own (without the help of any external heat), is called spontaneous combustion.

        The burning of white phosphorus on its own at room temperature is an

        example of spontaneous combustion. Combustion of coal dust is also an  

        example of spontaneous combustion.

3.           Explosive Combustion( or Explosion) :- A very fast combustion reaction in   

       which a large amount of heat, light and sound are produced, is called

       explosive combustion( or explosion). The fire works( crackers etc) which we

       explode during festivals work on the explosive combustion of substance. 

Q NO 17:-What is ignition temperature?

ANS:-The lowest temperature at which a substance catches fire is called its ignition temperature.

TOPIC :- CHEMICAL EFFECTS OF ELECTRIC CURRENT          

 CLASS 8^TH                                (SCIENCE)   

Electric current: An electric current is defined as the ordered motion of electric charges. i.e.  The rate of flow of charge is called electric current or in other words the magnitude of the current 'I' is the charge flowing in the circuit in one second. Mathematically current is expressed as

        Current (I) = Charge (coulomb) / Time (Second)          

OR                   I = Q/t

    Where 'Q' is charge and ‘t’ stands for time. The unit of electric current is 'ampere' (A). 

 1 ampere = 1coulomb/second

One ampere is defined as the current flowing through a conductor when the flow of one coulomb of charge flows in one second. One coulomb is defined as the quantity of charge flowing through a conductor per unit second.

Conductors: Substances which allow electricity to pass through them easily are called conductors. These are made from materials which have low resistances. Metals like copper, aluminium, silver, iron, brass and also salt solutions are good conductors of electricity.

Insulators: Substances which do not allow electricity to pass through them easily are called insulators. These are made from materials which have a high resistance. Some substances like  air, plastic, cotton, rubber, wood, paper, glass, pure water, etc are insulators.

Do liquids conduct electricity? Some liquids are good conductors and some are poor conductors of electricity. Water conducts electricity in the form of ions. It is a polar solvent and dissolves everything in it. A good electrolyte converts in the form of ions in water and conducts electricity. Electricity is the flow of charged particles (i.e. ions, electrons or protons); in a liquid, the electrons can pass on charge so some liquids are very good electrical conductors. Most liquids that conduct electricity are solutions of acids, bases and salts.

Examples of Liquid Electrical Conductivity: some of the important ones are as follows:

1.      Conductivity of electricity through water (due to the fact the normal water have ions in it).

2.      Conductivity of electricity through Ethanol (because ethanol develop opposite ions in the solution).

3.      Conductivity of liquid in Ethylene Glycol (because ethylene glycol also gives ion in solution and this create region of opposite charges resulting in flow of electrons and then electricity).

4.      Conductivity of electricity in Molten Wax.

5.      Conductivity of electricity in Molten Sugar solution.

6.      Conductivity of electricity in Molten Salt solution.

LED (Light Emitting Diode): The full form of LED is Light Emitting Diode. It is like a bulb which can glow even at a feeble current

supply. Ordinary bulbs can not glow when the current supply is low. So they consume more current and are

therefore, costly. Since LED consumes much lower electricity so, they are economical.LEDs are available

in many colours such as, red, green, yellow, blue etc. They find applications for many purposes like in traffic

signals, on railway platforms for various indicators etc.

Electrode: An electrode is a conductor through which electric current is passed. Found in variable forms, electrodes may be wires, plates, or rods. An electrode may be constructed of metal, such as copper, silver, lead, or zinc. However, an electrode may also be made of a nonmetal substance, such as carbon.An electrode passes current between a metallic part and a nonmetallic part of an electrical circuit. Most frequently, conductors that are metallic carry electrical current. In other circuits, however, current is passed through a nonmetallic conductor.

In an electrochemical cell, an electrode is called either an anode or a cathode. An anode is an electrode at which current leaves the cell and oxidation takes place. For example, an anode is the positive electrode in a storage battery.A cathode is described as a negative electrode. Current enters the cell at the cathode and reduction takes place. Electrons are repelled from the cathode.

Difference between anode and cathode: Cathodes and anodes are types of electrodes that conduct electrical currents either into or out of an electrical device. A cathode typically acts as a

positively charged terminal while an anode usually functions as a negatively charged terminal. Cathodes and anodes will sometimes function in reverse polarity in certain types of devices. As a general rule, when a device is discharging electricity, the current flows out of the cathode terminal. When a device is being charged with electricity, the current flows into the cathode causing it to function as the anode while the anode functions as the cathode.

Electrolyte: An electrolyte is a liquid substance which acts as a medium to conduct electricity. Anelectrolyte is full of ions, which are atoms that have some sort of net electric charge, either

positive or negative. A diluted electrolyte has a relatively small amount of ions for its volume, while a concentrated electrolyte has a high amount of ions.

Electroplating: Electroplating is the process of coating a desired metal on another metal surface using electric current. It is one of the most common applications of chemical effects of electrical current. Metallic plate and the substance requiring coating are dipped in conducting solution with conducting wires. The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the solution starts breaking and free metallic particles get deposited on the object at the negative terminal of battery. In this way we can get a coating of desired metal on any object bypreparing suitable conducting solution and using suitable electrodes.

                                    

 

 

 

 

 

 

 

 

 

 

 

Advantagesof electroplating: Electroplating is a very useful process and has many advantages

1.      It is used to coat metal surfaces with another metal having desired properties.

2.      It saves certain metal surfaces from rusting, corrosion etc.

3.      Coating of chromium on other metals give luster to objects and better corrosion resistance.

4.      Cheap metals like iron, aluminium etc. can be coated with costly metals like silver, gold etc. to givethem rich look as in case of artificial jewellary.

5.      With the help of this process we can reactive metals like iron etc. less reactive afterelectroplating them with tin, zinc etc. to make them more useful for certain purposes

                                      TEXTUAL QUESTIONS

 

Q NO 1:- Fill in the blanks

a)      Most liquids that conduct electricity are solutions of acids, bases and   salts.

b)      The passage of an electric current through a solution causes    chemical effects.

c)      If you pass current through copper sulphate solution, copper gets deposited on  

     the plate connected to the negative terminal of the battery.

d)      The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

 

Q NO 2:-When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

ANS:-The reason is that the solution conducts electricity and is a good conductor.

Q NO 3:-Name three liquids, which when tested in the manner shown in fig  

 8.9 may cause the magnetic needle to deflect?

ANS:- Acids, Bases and Acidulated water.

Q NO 4:-The bulb does not glow in the setup shown in Fig 8.10. List the possible reasons. Explain your answer?

ANS:-The setup shows no glowing of the bulb but it does not mean that liquid is not conducting electricity. The current may be so weak that it cannot make the buglow. So, as to test for surity, LED can be used which glows for very minute currents.

Q NO 5:-A tester is used to check the conduction of electricity through two liquids, labeled A & B,  it is found that the bulb of the tester glows brightly for liquid A while it glows very dim for liquid B, you would conclude that.

ANS:-Liquid A is better conductor than Liquid B.

Q NO 6:-Does pure water conduct electricity. If not, what can we do to make it conducting?

ANS:-Pure water is very poor conductor of electricity. Pure water can be made conducting by adding few drops of dilute sulphuric acid. The water so obtained is called acidulated water.

Q NO 7:-In case of fire, before the fireman use the water hoses, they shut the main electricity supply for the area. Explain why they do this?

ANS:-Pure water is an insulator but tap water is a good conductor of electricity. To avoid electro-conduction, fireman usually shut off the supply before using water hoses.

Q NO 8:-A child staying in coastal region tests drinking water and also sea water with his tester. He finds that compass needle deflects more in case of sea water. Explain?

ANS:-Sea water is rich in salt concentration. So, compass needle is deflected more in the sea water as compared to the drinking water.

Q NO 9:-Is it safe for electrician to carry out electrical repairs outdoors during heavy downpour. Explain?

ANS:-No, it is not safe for an electrician to carry out electrical repairs outdoors during heavy downpour because water is a good conductor of electricity, So electrician can get an electric shock.

Q NO 10:-Paheli had heard that rainwater is as good as distilled water. So, she collected some rain water in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reason?

ANS:-No doubt rain water is pure like distilled water. But  the environment is contaminated with many impurities. These impurities get dissolved in rain water, making it a good conductor of electric current.

Q NO 11:-Prepare a list of objects around you that are electroplated.

ANS:-1.Handle bar of cycle 2. Wheel rims 3. Artificial -ornaments  4. Bath Taps  5. Kitchen gas burner

Q NO 12:-The process that we saw  in Activity 8.7 is used for purification of copper.  A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?

ANS:-Thick rod of impure copper is to be attached to the positive terminal of battery as pure copper moves to the electrode connected to negative terminal of the battery.

 8TOPIC:-FORCE & PRESSURE                       PREPARED BY:- DAVOOD SIR.                                                     CLASS :-8TH                                                                                                                                                    

Force: The force is defined as an external influence which tends to set a stationary body in motion or tends to change the speed and direction of a moving body or which tends to make the moving body to come to rest. Force is a vector quantity with magnitude as well as direction. The S.I. unit of force is ‘Newton’.

Unit of force: The S.I. unit of force is Newton, and is defined as the force required to produce an acceleration of 1 m/s² in a body of mass 1 kilogram.

                        i.e.       1 Newton = 1 kg x 1 m/s²                    or         1N = 1 kgm/s²

From the unit of force, it is clear that force is the product of mass and acceleration.

            i.e.Force = Mass x Acceleration

Effects of Force: Some of the important effects of force are.

i.                    A force can change the state of motion of a body. i.e. it can make a stationary body to move and increase or decrease the speed of a moving body.

ii.                  It can change the direction of motion f a moving body.

iii.                It can change the shape and size of a body.

Balanced Forces: When the resultant of all the forces acting on a body is zero, then the forces are said to be balanced forces. A body under the balanced forces does not change position of rest or of uniform motion and it appears as if no force is acting on it.

e.g.  Suppose a heavy box is lying on the ground, when we push it. It will not move though four forces are acting on it. i.e. the force of our push, force of gravity and force of reaction. Since the four forces are acting on the box and it does not move at all. This shows that the resultant of all forces acting on it is zero. Therefore, the box behaves as if no force is acting on it. Thus the forces acting on the stationary box are balanced forces.

Unbalanced force: When the resultant of all the forces acting on an object is not zero, then the forces are called as unbalanced forces. When unbalanced forces act on a body, they produce a change in its state of rest or of uniform motion.

e.g. suppose a toy car is lying on the ground. When we push it, it will move. There are four forces acting on it. i.e. force of our push, force of friction, force of gravity and the force of reaction of ground. In this case the force of gravity on the car and the force of reaction of ground are equal and opposite. So they balance each other. But the force of our push is however greater than the force of friction. So they cannot balance each other. Thus the resultant of all forces acting on the toy car is not zero and therefore the forces are unbalanced.

Contact force: Forces which act on a body directly or through a connector are called contact forces. If a body A is in contact with another body B, then A can exert a force on B and B can exert a force on A. These forces are called as contact forces. The different types of contact forces are muscular force, mechanical force, frictional force and collision force etc.

i.        Muscular force: The force resulting due to the action of muscles is known as muscular forces. The forces applied in the act of pushing, pulling or lifting things around us are muscular forces.

ii.      Collision force: When two objects collide with each other, the contact force that comes into play is known as collision force. e.g. Force of collision between a bus and a car is a contact force.

iii.    Mechanical force: If the force is generated by the machines to make a body move, it is called a mechanical force.

iv.     Frictional force: when a body is slided over a rough surface, a force acts on the body parallel to the surface in direction opposite to the motion of the body. This force is called the frictional force.

Non-contact Forces: The forces which act on bodies without being physically touched are called the non contact forces. These forces are acting from a distance on an object and are also known as action at a distance force.

1.       Gravitational force:- The force due to pull of gravity is called the gravitational force. It is the gravitational force due to which a body released from a height falls down. Falling of a ball from the top of a building.

2.       Electrostatic force: The force between the two point charges placed at a separation is called the electrostatic force. Two like charges repel while the unlike charges attract each other. Force of attraction produced by a comb when rubbed with hairs and attracts the bits of paper.

3.      Magnetic force:-The force between the two magnetic poles placed at a separation is called the magnetic force. e.g. an iron piece attracted by a bar magnet.

Friction: Friction is a force that opposes the motion or tendency of motion between two surfaces in contact with each other.

Advantages of friction:-

1) Safe walking on the floor, motion of vehicle etc. are possible due to friction.

2) Nails, screws etc. are driven into walls, wooden surfaces etc. due to friction.

3) Writing with pens, pencils, holding objects (things) with hands etc is possible due to friction.

4) A match stick is lightened due to friction.

Disadvantages of friction:-

1) due to friction wear and tear of engine occurs.

2) due to friction some energy gets converted into heat which goes as waste.

3) The large amount of power loss in engines due to friction.

Pressure: Pressure is the defined as the force per unit area applied in a direction perpendicular to the surface of an object. Pressure is an effect which occurs when a force is applied on a surface. The standard unit for pressure is the Pascal, which is a Newton per square meter.                                                                             

Unit of pressure: In S.I. system, force is measured in newton and area in square meter. Therefore, S.I. Unit for pressure is the Pascal (Pa), equal to one newton per square meter (N/m² or kg·m⁻¹·s⁻²). One Pascal is defined as the force of one newton applied on an area of one square meter. i.e. 1 Pa = 1 N/m². The total force acting on a given surface is known as thrust.

Therefore,       pressure = thrust/area

Pascal’ law: Pascal's law states that if pressure is applied at any point in a liquid, it is transmitted equally throughout the liquid.                                                                                     For example when the cork of a bottle filled with water is pushed down, pressure is applied on the water in the bottle. This pressure is equally transmitted throughout the liquid and thus the walls of the bottle are pushed from inside by the liquid. Under extreme, pressure, the glass breaks and the bottle explodes.

Atmospheric pressure: The atmosphere is the layer of air around the earth. It extends up to 1000 km above the surface of the earth and has a total weight of 4.5x10¹⁸ kg (i.e., five million billion tons). This weight exerts a pressure on the surface of the earth which is called atmospheric pressure. Barometer is a device used to measure the atmospheric pressure or air pressure. Atmospheric pressure or air pressure is also called Barometric pressure. Evangelista Torricelli invented the mercury barometer.At sea level it is about 10⁵ Pa. We do not normally feel the large atmospheric pressure because the pressure inside our bodies is almost the same as the external pressure and so it is balanced.  At high altitudes the air pressure is less, therefore the breathing is difficult and nose bleeding may occur. Hence, modern aircrafts have pressurised cabins in which air pressure is increased sufficiently to safeguard the passengers and the crew.

Vacuum:A vacuum is a volume of space that is essentially empty of matter, so that gaseous pressure is much less than standard atmospheric pressure or simply “free space”. To create such free space/empty matter having pressure less than atmospheric pressure needs a device which is called vacuum pump. A vacuum pump is used to removes gas molecules from a sealed volume in order to leave behind a partial vacuum.

Mercury Barometer: A simple barometer can be prepared in the following manner:

Take a hard glass tube about 1m long. Fill the tube completely with clean dry mercury. Close the one end of the tube with your thumb and invert it over a trough filled with mercury, with the open end of the tube dipping into mercury. Remove your thumb only when the open end of the tube is well immersed into the mercury in the trough. Hold the tube in the vertical position by fixing it to a stand. On removing the thumb, you find that some mercury from the tube flows into the trough. The mercury column now stands up to a height of 760 mm above the mercury surface in the trough. He explained that the column of mercury was supported in the tube by the atmospheric pressure acting on the surface of the mercury in the trough. Thus, the atmospheric pressure can be ‘indirectly’ measured by the column of mercury it can support. Therefore, the atmosphere pressure of 760 mm at a place implies that its magnitude is such that it supports a column of mercury 760 mm long.

Q NO 1:-Give two examples each of situations in which you push or pull to change the state of motion of objects.

ANS:-  (1).Opening or shutting a door

            (2).A cricket ball hit by a batsman  

Q NO 2:-Give two examples of situations in which applied force causes a change in the shape of an object.
ANS:-   (1).Rolling a ball of flour dough for making a chapati at home

             (2).Bursting of an inflated balloon by pressing between the palms.

Q NO 3:-Fill in the blanks in the following statements:
(a) To draw water from a well we have to apply the force of pull at the rope.
(b) A charged body attracts or pulls  an uncharged body towards it.
(c) To move a loaded trolley we have to either pull it or push it.
(d) The north pole of a magnet repels  the north pole of another magnet.

Q NO 4:-An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms: 

     muscular, contact, non-contact, gravity, friction, shape, attraction
(a) To stretch the bow, the archer applies a force that causes a change in its shape.
(b) The force applied by the archer to stretch the bow is an example of muscular force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.
(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to  friction of air.
Q NO 5:-In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.                                                                                    

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.                

(d) An athlete making a high jump to clear the bar at a certain height.                              

ANS:- 

Situation		Agent	Object	Effect
(a) Squeezing a piece of lemon between the fingers to extract its juice.		Muscular Force of Fingers	Lemon Outer Surface	Shape of the piece of lemon gets changed and juice gets extracted.
(b) Taking out paste from a toothpaste tube.		Muscular Force of Fingers	Wall of Tube and Paste	Shape of the tube gets changed on pressing  and paste is squeezed out.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.		Weight of load by Force of Gravity	Spring	As the other end of the spring is fixed to wall, so the spring will expand downward.
(d) An athlete making a high jump to clear the bar at a certain height.		Muscular Force	Weight of athlete (Force of Gravity)	The athlete is able to lift his weight to jump across the bar at certain height

Q NO 6:- A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
ANS:-When  A blacksmith hammers a hot piece of iron while making a tool, its shape gets changed into a desired shape of tool.
Q NO 7:-An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall? 
ANS:-When we rub, an inflated balloon with a piece of synthetic cloth, its surface gets charged due to electrostatic force. On pressing it against a wall, the charged surface of balloon, due to electrostatic force, attracts uncharged surface of the wall and the balloon sticks to the wall. 
Q NO 8:-Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
ANS:-The forces acting on the plastic bucket containing water, held above the Ground Level are : 

 (a).Muscular Force which is being exerted to pull (lift) the weight of filled bucket, caused by force of gravity.                                                                                                                           (b).The force of Gravity, in the form of weight of bucket, acting in downward and opposite direction of muscular force

The forces acting on the bucket do not change its state of motion, as muscular force causing upward pull is cancelled out by downward pull of gravity.
Q NO 9:-A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
ANS:-When a rocket is fired upwards to launch a satellite, two forces acting on the rocket immediately after leaving the launching pad are : 
1. Combined weight of the rocket and payload ( Satellite), caused by the force of gravity, acting in the downward direction, towards the center of the earth

2. The force of thrust, caused by the burning of propellant fuel in the rocket. The force of thrust which exceeds force of gravity, acts in the opposite direction of gravity, and makes the rocket move upward 

Q NO 10:-When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure                                                                                                                     

ANS:- (c) shape of rubber bulb and (d) atmospheric pressure
On releasing the pressure on the bulb of dropper, it tries to regain its original form with greater volume earlier, inside. As the opening of dropper tube is dipped in water, water rises up to fill empty inside of dropper due to atmospheric pressure on the outer surface of water.

REACHING THE AGE OF ADOLESCENCE     

                   

Puberty: Puberty is the time in which sexual and physical characteristics mature. It occurs due to hormone changes. The changes allow us to become capable of reproduction.

 

Adolescence: Adolescence is the time between the beginning of sexual maturation (puberty) and adulthood. It is a time of psychological maturation, which a person becomes "adult-like" in behavior.

Adolescence is roughly considered to be the period between 13 and 19 years of age. The adolescent experiences not only physical growth and change but also emotional, psychological, social, and mental change and growth.

 

Changes at puberty:

Boys and Puberty: Adolescence is the time between childhood and adulthood. It lasts roughly from age 9 until adulthood. Adolescence includes puberty, physical changes, a change in thinking ability, and all the social and emotional changes that happen during this stage of life. Adolescence can be an exciting time and a tough time in a boy's life. The changes that happen to a boy's body during puberty.

 

Physical Changes During Puberty for Boys:

i.           Height and weight increase.

ii.         Body hair grows in the pubic area, under the arms, and on the face, and becomes thicker on the legs.

iii.       Muscles become stronger.

iv.        Vocal cords get thicker and longer - boys' voices deepen.

v.          The body develops an increased number of red blood cells.

vi.        Sweat and oil glands become more active, and body odor changes.

vii.      Acne can develop.

viii.    Some boys develop small and temporary breast tissue.

ix.        Reproductive system begins to work.

 

Girls and Puberty: Adolescence includes puberty, the physical changes, a change in thinking ability, and all the social and emotional changes that happen during this stage of life. It lasts roughly from age 9 until adulthood. Adolescence can be an exciting time and a tough time in a girl's life. The changes that happen to a girl's body during puberty.

 

Physical Changes During Puberty for Girls

i.         Breasts develop.

2. Height and weight increase.
3. Hips and waist become more defined.
4. Menstruation begins.
5. Mood changes may occur.
6. Body hair grows in the pubic area, under the arms, and becomes thicker on the arms and legs.
7. Muscles become stronger.
8. Fat tissue normally increases.
9. Vocal cords get thicker and longer.
10. Sweat and oil glands become more active, and body odor changes.
11. Acne may develop.
12. Reproductive system matures.

 

 

 

 

 

Secondary sexual characters:

The secondary sexual characteristics begin to appear during puberty as a result of hormonal stimulation. They become apparent first in females, a little later in males. By the time their physical growth is completed, the bodies of men and women show several marked differences.

 

Endocrine glands and their functions:-

i.              Thyroid gland: It is a soft butterfly shaped gland and secretes the thyroxin hormone which controls growth and development. Its excessive secretion causes thinness, nervousness while as its less secretion causes overweight and sluggishness.

ii.            Pancreas: Pancreas produces the hormone called insulin, which controls level of sugar in body. Less secretion of insulin causes diabetes.

iii.          Parathyroid: Parathyroid secretes the hormones called as parathormone which controls level of calcium in body.

iv.          Adrenal gland: These are a pair of cap shaped organs lying at the top in each kidney. It secretes the hormone cortisone, which converts excess of proteins into sugar.

v.            Ovary: Ovary produces Oestrogen and Progesterone, which controls the sexual characteristics in females, maintains pregnancy and child birth.

vi.          Testis: Testis produces testosterone, which controls development of secondary and accessory sexual characteristics in males.

vii.        Pituitary gland: These glands secretes growth hormones like ADH, ACTH, FSH and TSH, which regulates tissues and bones growth, controls the amount of water reabsorbed by the kidney, stimulates adrenal cortex to male cortisone, stimulates the ovary to produce oestrogen and stimulates thyroid to make thyroxin respectively.

viii.      Thymus: It secretes the hormones thymosine which controls and develops body resistance.

ix.           Pineal: It is a small reddish grey vascular solid body lying between the two cerebral hemispheres of the brain. It secretes melatonin hormone which regulates the working of gonad.

 

Hormonal action: The endocrine system acts by releasing hormones that in turn trigger actions in specific target cells. Receptors on target cell membranes bind only to one type of hormone. More than fifty human hormones have been identified; all act by binding to receptor molecules. The binding hormone changes the shape of the receptor causing the response to the hormone.

 

Role of hormones in initiating reproductive function:  The human body also possesses ductless glands which release their secretions directly into the bloodstream. These glands are called endocrine (Greek: internally secreting) glands. Their secretions, which may stimulate or regulate the functioning of various other, often remote organs, are known as hormones (from the Greek hormaein: to arouse). Every human body contains a number of endocrine glands and many different hormones which serve a great variety of purposes. The following paragraphs restrict themselves to a discussion of those hormones that affect a person's sexual and reproductive capacities.                                                                                                            

                 In regard to sex and reproduction, the most important endocrine glands are the pituitary gland and the male and female gonads or sex glands. The pituitary gland is located at the base of the brain. It is sometimes called the "master gland" because its hormones stimulate and coordinate the other endocrine glands. Among the pituitary hormones that are of particular interest here are FSH (follicle-stimulating hormone) and LH (luteinizing hormone). They stimulate the male and female gonads to produce hormones of their own.                                                                                                                                                                     The gonads or sex glands are the testicles in the male and the ovaries in the female. The hormones produced by the gonads are called gonadal hormones, and they can be divided into clearly distinct groups. One group of hormones that are particularly prominent in mature males are known as androgens. Another group of hormones particularly prominent in mature females are known as estrogens. (The female gonads also produce still another hormone called progesterone, which is important for a woman's reproductive life.) However, while there is a greatest amount of androgens in men and of estrogens in women, both groups of hormones are present in every individual. The gonadal hormones play an important role in a person's sexual maturation.

 

Role of hormones in metamorphosis : As in insects, a complex interaction of hormones in the amphibian larva precipitates metamorphosis. Ultimately, two major classes of hormones act together to control amphibian metamorphosis: the thyroid hormones (made by the thyroid gland) and prolactin (made by the pituitary gland). Thyroid hormones function somewhat like the molting hormones of insects, in that an increase of their concentration relative to prolactin leads to metamorphosis of the larva into the adult. Prolactin functions somewhat like the juvenile hormones of insects, in that it tempers the action of the thyroid hormones. In most species, thyroid hormones increase dramatically in concentration during metamorphosis and this stimulates resorption of certain larval organs and differentiation of new adult organs.

 

Sex Determination:- During the formation of gametes, the females will have only one type of gametes, all with one X chromosome. However, the males will produce two types of gametes or sperms, half with X chromosome and half with Y chromosome. Thus the sex of a zygote is determined by which male gamete fuses with the female gamete. If the X gamete fuses with the female gamete (also X), the zygote will be a female. If the Y gamete fused with the female gamete, the zygote will be a male. This type of sex determination is called XX-XY type.

 

Reproductive health: The physical and mental well being of an individual is regarded as an individual’s heath.  Adolescents have unique reproductive and sexual health needs. Therefore the adolescents growing body require proper care and maintenance, which can be

i.                    Adolescence is the stage of rapid growth and development, hence the diet for an adolescent has to be planned carefully keeping in view the requirements with respect to the balanced diet which includes proteins, carbohydrates, fats, and vitamins in requisite proportions.

ii.                  Having regular bath everyday in order to avoid the bacterial infections due to increased activity of sweat glands.

iii.                Adolescents should take walks, exercise and play outdoor games regularly so that they have proper physical and mental growth.

iv.                Adolescents should be given proper education about the bad habits. So that they may not be confused or insecure about drugs and their usage.

AIDS: Acquired Immunodeficiency Syndrome (AIDS) is caused by a retrovirus known as the Human Immunodeficiency Virus (HIV), which infects cells of the human immune system, destroying or impairing their function.         

 

Modes of Transmission of AIDS: HIV is transmitted through unprotected sexual intercourse, transfusion of contaminated blood, sharing of contaminated needles, and between a mother and her infant during pregnancy, childbirth and breastfeeding.

Adam’s apple: A familiar anatomic feature in the front of the neck that is due to the forward projection (outgrowth) of the thyroid gland the largest and most prominent cartilage of the larynx. The thyroid cartilage tends to enlarge at adolescence, particularly in males. Enlargement of the Adam's apple is considered, like pubic hair growth, one of the secondary sexual characteristics. The primary purpose of the structure is to protect the delicate voice-box from injuries.

Menstruation: The menstrual cycle is the process by which a woman's body gets ready for the chance of a pregnancy each month. The average menstrual cycle is 28 days from the start of one to the start of the next.

Most menstrual periods last from three to five days. At about the age of 10 to 13 years, the ovaries of females are stimulated by the follicle stimulating hormone (FSH) of the pituitary. This is called the onset of puberty and is accompanied by release of hormones oestrogen and progesterone. These hormones control the production of ova or eggs and appearance of secondary sexual characteristics. Unlike males where sperms can be produced throughout the life of man, in females the reproductive phase only lasts till the age of 45-50 years. This phase is characterized by the presence of menstrual cycle. Each menstrual cycle typically occurs in about 28 to 30 days. Thus it occurs every month.

Menarche:-  Menarche is the initiation of menstrual cycle & occurs at the age of 11 to 13 years

Menopause: Menopause is the cessation of menstrual cycle for life time & occurs at the age of 45 to 50 years.

 

                                          TEXTUAL QUESTIONS

Q NO 1:-What is the term used for secretion of endocrine glands responsible  

                for changes taking place in the body?

ANS:-Hormone is the term used for secretion of endocrine glands responsible for  

          changes taking place in the body.

 

Q NO 2:-Define Adolescence?

ANS:-The period of life, when the body undergoes changes, leading to

          reproductive maturity is called adolescence. It begins around the age of 11 

          and lasts upto 18 or 19 years. Since this period covers the teens (13 to 19),

          adolescents are also called teenagers.

 

Q NO 4:-What is  menstruation? Explain.

ANS:-The rhythemic changes in the uterus which occur about every 28 days

          throughout the reproductive cycle of women except the pregnancy is

          called menstrual cycle.

            The female sex hormones initiate the thickening of the uterine wall for the implantation of a fertilized ovum or egg.  If the ovum is not fertilized the  lining  wall of uterus is broken down and is discharged from the body. This is called menstruation. Normally the menstrual cycle starts at the age of 10 to 12 years and stops at the age of 45 to 50 years when menopause is reached.

 

Q NO 4:-List changes that take place at Puberty?

ANS:-The changes that take place at  puberty are as follows:-

1.      Increase in height:- the most conspicuous change during puberty is the sudden increase in the height of boys and girls.

2.      Change in body shape and appearance:- During puberty, the shoulders in boys become broader, chest becomes wider and in girls the region below waist becomes wider and breasts begin to develop.

3.      Change in voice:- the voice box of person begins to develop at puberty. The voice box in boys is larger than in girls. The growing voice box in boys can be seen as a protruding part of throat called Adam’s apple. Generally, boys have deep voice and girls have high- pitched voice. Sometimes in boys, the muscles of the growing voice box goes out of control and voice becomes hoarse but this state remains only for few days.

4.      Increased activity of sebaceous and sweat glands:- During puberty, the sebaceous and sweat gland secretion increases. This causes acne and pimples on the face of a person.

5.      Sex organs become capable of reproduction:- During puberty, the sex organs in humans become capable of reproduction. In males, testes and penis are the main sex organs while as in females oviducts and uterus are the main sex organs. In males, testes start producing sperms, they release the male sex hormones called testosterone. In females, ovaries start to release mature eggs (ovum) and hormone estrogen and progesterone.

 

Q NO 5:-Prepare a table having two columns depicting names of endocrine

               glands and hormones secreted by them.

 

S.NO	ENDOCRINE GLANDS	HORMONE SECRETED
1	Thyroid gland	Thyroxine
2	Pancreas	Insulin
3	Adrenal gland	Adrenalin, sex hormones
4	Pituitary gland	Growth hormone,
5	Testes	Testosterone
6	Ovaries	Progesterone, Oestrogen

 

Q NO 6:-What are sex hormones? Why are they named so? State their  

                function.

ANS:-The hormones secreted by testes and ovaries are called sex hormones.

          These hormones  are responsible for the development of male and female  

          secondary sexual characters that is why they are named so.

 

Functions of sex hormones:-

v  Male sex hormone (Testosterone):- It is secreted by testes. It causes changes in boys like growth of facial hair. It also stimulates spermatogenesis.

v  Female sex hormones (Estrogen):- It is secreted by ovaries. It controls the development of secondary sexual characters in females, appearance of mammary glands, etc. It maintains pregnancy.

 

Q NO 7:-Choose the correct option.

      (A). Adolescents should be careful about what they eat, because

  ANS:-Proper diet is needed for the rapid growth taking place in their body.

       (B). Reproductive age in women starts when their

ANS:-Menstruation starts .

      (C). The right meal for adolescents consists of

ANS:-Chapati, Daal, vegetables.

 

Q NO 8:-Write short notes on:-

1.      Adam’s apple:-  The voice box or larynx in a grown up boy can be seen as a protruding part of the throat called Adam’s apple. In girls, the larynx is much smaller in size and is hardly visible from outside. So, girls don’t develop Adam’s apple at puberty.

2.      Secondary sexual characters:-  The secondary sexual characters are controlled by hormones which distinguish between sexually mature boys and girls but aren’t directly involved in reproduction. The body parts other than sex organs develop special features which makes it easier to distinguish between boys and girls like growing of facial hair, development of breasts etc.

3.      Sex determination of the unborn baby:- The sex of baby is determined by the type of sex chromosomes present in the fertilized egg or zygote from which baby develops. There are two types of sex chromosomes. They are X chromosome and Y chromosome.

          A female has only X chromosome in all her gametes called eggs while as a male has X as well as Y chromosomes( half sperms have X chromosomes and other half have  Y chromosomes). If a sperm carrying X chromosomes fertilizes an egg cell, having X chromosome then the zygote formed will have XX combination of sex chromosomes due to which the child born will be a girl. If a sperm carrying Y chromosome fertilizes an egg cell, having X chromosome, then the zygote formed will have XY combination of sex chromosomes due to which the child born will be a boy.

Thus, the sex of unborn baby depends on whether the zygote formed at the time of fertilization has XX combination of sex chromosomes or XY combination of sex chromosomes. XX combination of sex chromosomes make the child a girl and XY combination of sex chromosomes make the child a boy.

            It is the sperm of man which determines the sex of the child. The egg cells of woman cannot decide the sex of the child because all the egg cells contain the same sex chromosomes i.e; X Chromosome. Hence ,  the father is responsible for the sex of the baby which is born. The belief that mother is responsible for the sex of baby is wrong.

TOPIC:-  METALS & NON-METALS               

 

Materials: Metal and Non-metals

Metals: Metals are defined as the elements which loose the electrons from their outermost shell to form the positive ions, i.e. they are electropositive elements. The electropositive behaviour of metals is due to low ionisation energies. It is this electropositive behaviour of metals which produces their characteristic chemical properties.

For example:   Sodium is a metal with atomic number 11, i.e. it has 11 electrons revolving around its nucleus with the following electronic configuration  2, 8, 1 with only one electron its outermost shell which it will donate to some other element to form the positive sodium ion.

i.e.       Na                                            Na⁺  +  e^-

                              (2, 8, 1)                                      (2, 8)        (Electron)

Some examples of metals are sodium(Na), Potassium(K), Magnesium(Mg), Calcium(Ca), Aluminium(Al), Copper(Cu), Gold(Au), Silver(Ag) etc.

 

Physical properties of metals: The important physical properties of the metals are

i.              Metals in their pure state possess shiny surface known as metallic lustre. Most of the metals lose their brightness when exposed to air for a long time and acquire dullness due to the corrosion. It is the shiny appearance that makes metals good reflectors of light.

ii.             Metals are highly malleable, i.e. metals can be drawn into sheets when beaten (hammered) without breaking. Gold and silver are the best malleable metals.

iii.          Metals are highly ductile, i.e. metals can be drawn into thin wires. All metals are not equally ductile silver is one of the best ductile metals.

iv.           Metals are good conductors of heat, i.e. metals can allow heat to pass through them. Silver is the best conductor of heat. The poorest conductor of heat among the metals is lead.

v.             Metals are good conductors of electricity, i.e. metals allow the electric current to pass through them and offer less resistance to the flow of current. Silver and copper are the best electrical conductors.

vi.           The metals are solid at room temperature.The only exception is mercury. Gallium also has melting point (30^oC) at the room temperature. It melts when held in the hand.

vii.         The metals possess high tensile strength. That is metals can be bent to a very large extent and heavy weights can be suspended from metallic wires without breaking the wire.

viii.       Metals possess high densities. Most of the metals possess densities greater than 5 g cm^-3. Among metals osmium is the heaviest metal with density 22 g cm^-3 and lithium is the lightest metal with density 0.5 gcm^-3.

ix.           Most of the metals are hard except some alkali metals like sodium and potassium which can be cut easily with a knife.

x.             All metals possess high melting and boiling points except mercury, gallium and alkali metals. Among metals tungsten has the highest and mercury has the lowest melting point.

xi.           Metals form homogenous mixtures with each other and also with non metals to form alloys. e.g. Brass is an alloy of copper and zinc.

xii.          Metals are generally sonorous, i.e. metals produce sound when hit with some other solid objects.

xiii.       Metals usually have a silver or grey colour except copper and gold which have reddish brown and yellowish colour respectively.

 

 

 

 

Chemical properties of metals: some of the important chemical properties of metals are.

i.        Reaction of metals with oxygen (air): All metals combine with oxygen to form their respective metal oxides. Metal oxides are basic in nature. Some of the metal oxides combine with water to form alkalis. Due to their basic nature metal oxides turns red litmus paper red. Metal oxides are ionic compounds formed by the transference of electrons from metal atom to oxygen atom.

e.g.                     4Na (s) + O₂ (g)                          2 Na₂O (Sodium oxide)

                                 Na₂O + H₂O                   2 NaOH (Sodium Hydroxide)

ii.      Reaction of metals with water: Metals react with water to from respective metal hydroxide (or metal oxide) and liberates the hydrogen gas. Less reactive metals like copper, silver,and gold do not displace hydrogen from the water. Some metals react with water vigorously and some metals do not react with water under ordinary conditions.

e.g.   Sodium and potassium react vigorously with cold water and displaces hydrogen gas.

                     2Na + 2H₂O                             2NaOH + H₂

                     2K +2H₂O                                 2KOH +H₂

      Magnesium reacts very rapidly with hot water to from magnesium oxide and it does not react with cold water.

                     Mg + H₂O                                MgO + H₂

      Zinc reacts rapidly but only with steam

                     Zn + H₂O (g)                            ZnO + H₂­

      Iron displaces hydrogen from water when steam is passed over red hot iron. The reaction is reversible in nature.

                     3Fe + 4H₂O                              Fe₃O₄ + 4H₂                             etc.

iii.    Reaction of metals with hydrogen: Most of the metals do not react with hydrogen. A few reactive metals such as sodium, potassium and calcium react with hydrogen to form ionic hydrides.

2Na +H₂                                   2NaH (sodium hydride)

2K + H₂                                    2KH (potassium hydride)

iv.     Reaction of metals with metal oxides: A more reactive metal can displace a less reactive metal from its oxide. e.g. Aluminium can displace iron from ferric oxide. But the reverse of such reactions is not possible.

2Al +Fe₂O₃                       2Fe +Al₂O₃

v.       Reaction of metals with acids: Metals usually displaces hydrogen gas from dilute acids. Only less reactive metals like copper, silver and gold do not react with dilute acids. Metals on reacting with acids produce salt and displace hydrogen gas.

e.g.         Sodium reacts with dilute hydrochloric acid with an explosive violence and hence show that sodium very reactive metal.

                                 2Na + 2HCl                              2NaCl + H₂

      Magnesium reacts rapidly with dilute hydrochloric acid to form magnesium chloride and hydrogen gas.

                                 Mg + 2HCl                               MgCl₂ + H₂

      Zinc combines with dilute hydrochloric acid, but less rapidly than magnesium. This shows zinc is less reactive than magnesium.

                                 Zn + 2HCl                                ZnCl₂ + H₂                                            etc.

vi.     Reaction of metal with metal salts (Displacement reaction): The basic principle of displacement reactions is that a more reactive metal can displace a less reactive metal from the solution of its salt.

e.g.         Zinc when combines with copper sulphate produce zinc sulphate solution and displaces copper, shows that zinc is more reactive than copper. But the reverse of this reaction is not possible.                    

         Zn _(s) +        CuSO_{4 (aq)}                                         ZnSO_{4 (aq)}      +   Cu _(s)

               _{(Zinc)     (Copper Sulphate)                           (Zinc Sulphate)                     (Copper)}

      Copper when combines with silver nitrate replaces silver to form copper nitrate. This showsthat copper is more reactive than silver.

                                 Cu _(s)      +        AgNO_{3 (aq)}                                             Cu(NO₃)₂          +  2 Ag                                 _{(Copper)                        (Silver Nitrate)                                     (Copper Nitrate)                 (Silver)}

 

Non-metals: Non - metals are defined as the elements which gain the electrons to form the negative ions, i.e. they are electronegative elements. Since large amount of energy is needed to remove one or more electrons from non metals, so non metals do not form positively charged ions. On the other hand, energy is released when a non metals accepts one or more electrons. Thus non metals readily form negatively charged ions by the gain of electrons. Therefore non-metals are electronegative elements.

For example:   Chlorine is a non metal with atomic number 17,  i.e. it has 17 electrons revolving round the nucleus in their orbits with the following electronic configuration 2,8,7 with 7 electrons in its outermost shell. It has to gain an electron from some other combining element to complete its outermost shell to from the negative chlorine ion.

                        i.e.       Cl         +          e ^-                                Cl^-

                                (2, 8, 7)            (Electron)                        (2, 8, 8)

Some examples of non-metals are Hydrogen (H), Oxygen (O), Nitrogen (N), Chlorine (Cl), Bromine (Br), Sulphur(S), Phosphorous (P), Carbon(C) etc.

 

Physical properties of non metals: Some of important physical properties of non metals are

i.           Non-metals do not possess any lustre (except iodine which is a non metallic solid but has lustre).

ii.         Non-metals are soft and brittle; non-metals can break into break into pieces when hammered except diamond which is the hardest known substance.

iii.       Non-metals are neither malleable nor ductile, i.e. non metals cannot be drawn into sheets and thin wires.

iv.       Non-metals are generally bad conductors of heat and electricity except graphite an allotropic form of carbon which is a good conductor of electricity du tot presence of free electrons in it.

v.         Non-metals are non sonorous substances. i.e. non metals cannot produce sounds when hit with a hard object.

vi.       Non-metals generally have low melting and boiling points except boron diamond, and graphite which have high melting and boiling points.

vii.     Non-metals have generally low densities, i.e. non metals are generally lighter than metals. Sulphur has the lowest density of 2.0g cm^-3.

viii.   Non-metals have low tensile strength. i.e. non metals can broke easily and cannot have the resistance to bear the force as that of the metals.

ix.        Non-metals can exist in solid, liquid, and gaseous states at room temperature. Carbon sulphur, phosphorous, and iodine are solid, bromine is the only non-metal in liquid state while as hydrogen, oxygen chlorine etc. are gaseous in state.

Chemical properties of non-metals: Some of the important chemical properties of non-metals are

i.              Reaction non-metals with oxygen: Non-metals when heated react with oxygen to form their respective oxides which are either acidic or neutral in nature and are never basic in nature. The non-metallic oxides are covalent compounds formed due to the sharing of electrons between the non metals and the oxygen atom.

e.g. formation of carbon dioxide molecule.

     

                              O         C          O                     OR                   O=C=O                       

 

The non-metallic oxides which react dissolve in water to form acids are called as acidic oxides. These oxides turn blue litmus paper red.

                              C(s)      +          O₂ (g)                           CO₂ (g)

The non-metallic oxides which neither react with acids nor with bases are called as neutral oxides. These neither turn blue litmus paper red nor red litmus to blue.

2C(s)    +          O₂ (g)                           2CO (g)

ii.            Reaction of non-metals with  water: Non-metals  usually do not react with water (or steam) to produce H² gas. It is because non-metals cannot reduce the hydrogen (H⁺) ions of water to hydrogen gas. However some highly reactive non-metals like fluorine reacts water to form oxygen and ozone.

2F₂ (g)   +         2H₂O (l)                                 4HF (aq)            +          O₂ (g)

                              3F₂ (g)  +    3H₂O (l)                                 6HF (aq)            +          O₃ (g)

iii.          Reaction of non-metals with dilute acids: Non-metals do not react with acids to displace hydrogen gas, it is because non-metals are electron acceptors and cannot supply electrons to H⁺ ions to reduce them to hydrogen gas.

iv.          Reaction of non-metals with chlorine: Non-metals react with chlorine to form respective chlorides. It is because non-metals combine with chlorine to form covalent chlorides by sharing electrons, and they cannot give electrons to chlorine atoms to form chloride ions. These covalent chlorides are generally volatile liquids or gases.

                         H₂ (g)   +         Cl₂ (g)           ^{Diffused Sunlight}            2HCl (g)

                         P₄                +  6Cl₂ (g)                                                4PCl₃

v.            Reaction of non-metals with hydrogen: Non-metals combine with hydrogen to form covalent hydrides. These hydrides are generally gases or liquids, but these hydrides do not conduct electricity.                                                                                                                                                        e.g. Hydrogen when combines with liquid sulphur at 440^oC or 713 K form hydrogen sulphide.                8H₂(g)  +          S₈ (l)                             8H₂S

vi.          Reaction of non-metals with salts: A more reactive non-metal displaces a less reactive non-metal from the solution of its salt.

e.g.when chlorine is passed through the solution of sodium bromide, bromine is displaced with the formation of sodium chloride.

                        2NaBr (aq)      +          Cl₂ (g)                              2NaCl (aq)        +      Br₂ (l)

vii.        Oxidising behaviour of non-metals: Non-metals have a strong tendency to accept electron to form negative ions. Therefore non-metals behave as oxidising agents.

e.g. fluorine is the strongest oxidising agent. It oxidises water to oxygen and hydrogen fluoride.

            i.e.       2H₂O    +          2F₂ (g)                          4HF (aq)          +          O₂ (g)

 

Difference between metals and non-metals :

METALS

NON-METALS

1.      Metals show metallic lustre ( shinyappearance). 2.      Metals are generally hard except sodium and potassium. 3.      Metals are malleable and ductile. (can be drawn into sheets and wires). 4.      Metals are good conductors of heat and electricity. 5.      Metals generally have high melting and boiling points, except mercury and gallium. 6.      Metals are sonorous (can produce sound when hit with a solid). 7.      Metals generally have high density. 8.      Metals generally have high tensile strength and cannot be broken easily. 9.      Metals are generally solid (except mercury gallium which are liquids) at room temperature. 10.  Metals are electropositive elements and can lose electrons. 11.  Metals form basic oxides 12.  Most of the metals displace hydrogen from water or steam. 13.  Metals which are more reactive than hydrogen displace hydrogen from dilute acids. 14.  Metals generally form ionic hydrides which are unstable. 15.  Metals have a strong tendency to lose electrons and hence behave as reducing agents. 16.  Metals generally combine with chlorine to form ionic chlorides.

1.      Non-metals do not show metallic lustre (Shiny appearance). 2.      Non-metals are generally soft except diamond and boron. 3.      Non-metals are neither malleable nor ductile. They are brittle. 4.      Non-metals are generally bad conductors of heat and electricity except graphite and gas carbon. 5.      Non-metals generally have low melting and boiling points. 6.      Non-metals are generally non sonorous (cannot produce sound when hit with a solid). 7.      Non-metals have generally low densities. 8.      Non-metals generally have low tensile strength and can be broken easily. 9.      Non-metals are either solids or gases at room temperature, only bromine is in liquid state at room temperature. 10.   Non-metals are electronegative elements and hence gain electrons to form negative ions. 11.   Non-metals form either acidic or neutral oxides. 12.  Non-metals generally do not react with water or steam except fluorine. 13.  Non metals do not react with dilute acids and hence do not displace hydrogen from dilute acids. 14.  Non-metals form covalent hydrides which are quite stable. 15.  Non-metals combine with chlorine to form covalent chlorides. 16.  Non metals have a strong tendency to accept electrons and hence behave as oxidising agents.

 

Corrosion of Metals: Corrosion is an oxidation reaction with atmospheric oxygen in the presence of water on the surface of a metal. Iron corrodes more quickly than most other transition metals to form an iron oxide. Corrosion or rusting of iron is accelerated in the presence of CO₂ and also in the presence of salt solution.                                                                                                                                                             The two conditions necessary for the corrosion of metals are

i.                    Presence of air (or oxygen) and

ii.                  Presence of water vapour (or moisture).

 

Prevention of Corrosion: The various methods used to prevent corrosion are

i.        The most common method used for preventing of rusting of iron objects is to coat their surfaces with paint.

ii.      Greasing and oiling of the metal surfaces also prevents the surface of metals from rusting.

iii.    Metals can also be prevented from rusting by the process of galvanization. The process of coating   iron objects with a thin layer of zinc is called galvanization. It is usually done bydipping the iron object in molten zinc. When zinc is coated on the iron objects, iron cannot come in contact with air and moisture and hence prevent rusting of iron.

iv.    Corrosion of metals can be prevented by coating with tin, chromium and nickel know as tin plating, chromium plating etc.

v.      Rusting of iron  can be prevented by alloying it to make stainless steel and other metals can also be prevented from rusting by alloying them with other metals, as alloys are corrosion resistant.

 

Alloy:An alloy is defined as a homogeneous mixture of two or more metals, or a metal and a non metal. i.e. An alloy is a mixture of two or more metals fused together in molten state. Metals when melted tend to dissolve in one another forming alloys. The various properties of a metal like malleability, ductility, strength, hardness, resistance to corrosion and appearance can be improved by mixing with other metals. Alloys have properties different from its constituents.Alloys are of three types: Ferrous alloys, Non ferrous alloys and Amalgams.

i.                    Ferrous Alloys: Those alloys which have iron as one of their constituents are called as ferrous alloys. e.g. Manganese steel ( Fe = 86%, Mn = 13% and C = 1%) and Nickel steel (Iron = 96 – 98 %, Ni = 4 – 2 %) etc.

ii.                  Non – Ferrous Alloys: Those alloys which does not have iron as one of their constituents are known as non-ferrous alloys. e.g. Brass ( Cu = 80%, Zn = 20%), Bronze (Cu = 90%, Sn = 10%).

iii.                Amalgam: Amalgams are special alloys that combine mercury and other metals in the periodic table. The amalgam of Hg, Ag and Zn is used in dental fillings. A solution of sodium metal in liquid mercury metal is called sodium amalgam. Zinc amalgam is used in voltaic cells.

Important alloys with their composition, properties and uses:

 

Uses of metals: The important uses of metals are

i.                    Metals like aluminium, copper stainless steel are used in making utensils used at home.

ii.                  Metals with high melting points are used in making electrical wires and bulb filament.

iii.                Metals are used in the manufacture of automobile, aeroplanes, ships, trains etc.

iv.                Un-reactive and expensive metals like silver and gold are used in making of jewellary.

v.                  Metals are used in the construction of buildings and bridges (reinforced concrete).

vi.                Metals are used in manufacturing of all machine parts and minting of coins.

vii.              Metals with low melting point like mercury is used in thermometers.

Uses of non-metals: The important uses of non metals are

i.                    Non-metals are used in the process of water purification.

ii.                  Non-metals are used in manufacturing of fertilizers to enhance the growth of plants.

iii.                Non-metals are used in the making of crackers.

iv.                Non-metals are used in the preparation of some antiseptics and ointments.

v.                  Non-metal like oxygen is essential for life is used by living organisms during the process of respiration.

 

Q NO 1:- Which of the following can be beaten into their sheets (a) Zinc

                (b) Phosphorus (c) Sulphur (d) Oxygen?

ANS:-Zinc.

 

Q NO 2:- Which of the following statements is correct?

a)      All metals are ductile.

b)      All non- metals are ductile.

c)      Generally metals are ductile.

d)      Some non- metals are ductile                                                                                          

ANS:- (c) Generally metals are ductile.

Q NO 3:- Fill ups:

ANS:- (a) Phosphorus is very  reactive non-metal.

           (b) Metals are conductors of heat and electricity.

           (c) Iron is more reactive than copper.

           (d) Metals react with acids to produce  hydrogen gas.

Q NO 4:- Mark  “T” if true and “F” if false.

ANS:-(a) Generally, non-metals react with acids .                     (T)

           (b) Sodium is very reactive metal.                                     (T)

           (c) Copper displaces zinc from zinc sulphate solution.  (F)

           (d) Coal can be drawn into wires.                                      (F)

Q5: Some properties are given below. Distinguish between metals and non- metals on the basis of these properties.

1.      Appearance  2.  Hardness   3.Malleability  4. Ductility.  5. Heat conduction  6. Conduction of Electricity.

 

 

S. no	PROPERTIES	METALS	NON-METALS
1.	Appearance	Silvery or grey in colour.	Different coloured
2.	Hardness	Solid at room temperature and hard except Hg.	Solid, liquid or gas at room temperature and brittle.
3.	Malleability	Can be beaten into sheets.	Non-malleable.
4.	Ductility	Can be drawn into wires.	Non-ductile.
5.	Heat conduction	Present	Absent
6.	Conduction of electricity	Possible	Not possible.

 

Q NO 6:-Give reasons of the following:-

a)      Aluminium foils are used to wrap food items .

          ANS:- Aluminium foils are used to wrap food items because aluminium is  

          malleable and less reactive to air and water.

b)     Immersion rods for heating liquids are made up of metallic substances ANS:- Immersion rods for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity.

c)      Copper cannot displace zinc from its salt solution.

          ANS:- Copper is less reactive than zinc. As a result it cannot displace zinc   
          from its salt solution.

d)     Sodium and potassium are stored in kerosene.

          ANS:- Sodium and potassium are very reactive metals. They react with air

          and water to  form respective oxides and hydroxides. So they are kept in  

          kerosene.

 

 Q NO 7:-Can you store lemon pickle in aluminium utensil?

ANS:-No, lemon pickle cannot be stored in aluminium utensil because acid present in lemon  pickle reacts with aluminium to produce poisonous chemicals, which cause food poisoning or   other health hazards.

 

 Q NO 8:-Match the terms in column A with those in column B

S.NO.	Column A	Column B
1.	Gold	Jewellery.
2.	Iron	Machinery.
3.	Aluminium	Wrapping food
4.	Carbon	Fuel
5.	Copper	Electric wire
6.	Mercury	Thermometers

 

 Q NO 9:-What happens when:

a)      Dilute sulphuric acid is poured on a copper plate.

ANS:- When sulphuric acid is poured on a copper plate, hydrogen gas is given out.

Copper + Sulphuric acid →Copper Sulphate + Hydrogen gas.

b)      Iron nails are placed in copper sulphate solution

ANS:- When iron nails are placed in copper sulphate solution, iron displaces copper from its salt to form iron sulphate.

Copper Sulphate +Iron  →Iron Sulphate + Copper.

Q NO 10:- Saresh took a piece of burning charcoal and collected the gas evolved in a test tube.

a)      How will she find the nature of gas?

ANS:-To test the nature of gas:

1.      Take blue/red litmus turn wise into the jar of gas collected. It will turn blue litmus red and red litmus will not be affected. This shows that gas is acidic in nature.

2.       Add some water to the jar. The liquid turns blue litmus red showing acidic nature of the gas.

 

b)     Write down word equations of all the reactions taking place in this process?

ANS:-When a charcoal is burnt, it reacts with oxygen to form an acid oxide called carbon dioxide.

      Carbon  +Oxygen   →Carbon dioxide

The carbon dioxide dissolves in water to form an acid called carbonic acid.

      CO₂  + H₂O  →H₂CO₃

                           (carbonic acid)

 

 

Q NO 11:-One day Rita went to jewellers shop with her mother. Her mother gave an old jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in the weight. Can you suggest a reason for the loss in weight?

ANS:-Jewellers usually use a chemical solution named aqua regia for cleaning the jewellery. This solution is capable of dissolving gold in it. So, loss in weight is found.

Q NO 12:-Why is phosphorus stored in water ?

ANS:-Non-metal Phosphorus like other non-metals does not react with water. On the other hand, when phosphorus comes in contact with air it readily combines with air to form phosphorus pentoxide which can easily catch fire. To protect it from coming in contact with air, it is placed in water.

Q NO 13:-Why sodium metal is stored in kerosene?

ANS:-Sodium is a highly reactive metal. It readily combines with oxygen when exposed to air and even sometimes it catches fire. It also reacts with water forming its hydroxide. To prevent its oxidation sodium is stored in kerosene.

Q NO 14:-Oxides of metals are basic in nature. Explain?

ANS:-Metals react with oxygen to form metal oxides. To test their nature we dissolve these metal oxides in water and then introduce red and blue litmus paper in their solution. Since the solution of oxides in water turns red litmus paper to blue, it shows that oxides of metals are basic in nature. 

 

                                                                                                                                                           

Light

LIGHT:-  Light is defined as a form of energy which enables us to see objects from which it comes and is reflected back. i.e. it is an invisible form energy that provides us sensation of sight. An object or a body which produces the light is known as source of a light and the sources of light may be natural or manmade. Sun is the most important source of light. Light is also known as radiant energy.

            The sources of light may be classified as luminous and non luminous sources due to their production and occurrence of light energy.

            Those sources of light which have their own light are known as luminous sources e.g. sun, stars, candle, electric lamp etc. while as those sources of light which do not have their own light but reflects and scatters light coming from luminous sources are known as non luminous sources. E.g. moon, book, wall etc.

Reflection of light: When a ray of light hits a surface, it bounces off or reflects and then reaches our eyes. This phenomenon by which a ray of light changes the direction of propagation when it strikes a boundary between different media through which it cannot pass is described as the reflection of light. Or in simpler words reflection is the bouncing back of light from a  surface. There are two types of reflection of light:

1.      Regular reflection or specular reflection:- Specular or regular reflection is the perfect, mirror-like reflection of light. In this type of reflection the reflected rays are also parallel to each other. Reflection in a mirror, a water surface and highly polished floors, are examples of regular reflections.

                      

2.      Irregular reflection or diffused reflection:-  Irregular reflection or diffused reflection takes place when a ray of light is incident on a wall or wood, which is not smooth or polished. In this case, the different portions of the surface reflect the incident light in different directions. In such cases no definite image is formed, but the surface becomes visible. It is commonly known as scattering of light. Thus diffused reflection makes non-luminous objects visible.

                       

 

Reflection of Light by a Plane Surface: The figure shows how a ray of light is reflected by a plane surface. Let MM' represent a reflecting surface. When a ray of light is incident on MM' in the direction IO it gets reflected along the direction OR. IO is the incident ray; O is the point of incidence and OR is the reflected ray. Let ON be the normal drawn perpendicular to the surface MM' at the point of incidence. The angle which the incident ray makes with the normal at the point of incidence is called the angle of incidence and is denoted by the letter 'i'. The angle that the reflected ray makes with the normal at the point of incidence is called the angle of reflection 'r'. Mirror is an example of a reflecting surface.                 The reflection at any plane surface is found to obey the laws of reflection. The laws of reflection are:

i.                    The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. 

ii.                  The angle of incidence is equal to the angle of reflection.

                                        

CHARACTERISTICS OF IMAGE FORMED BY A PLANE MIRROR

(I) The image formed by plane mirror is virtual (or unreal)

(ii) The image formed by plane mirror is behind the mirror.

(iii) The image formed in a plane mirror is  at the same distance behind the mirror as the object is in front of it.

(iv) The image formed in a plane mirror is of the same size as the object .

(v) The image formed by the plane mirror is laterally inverted.

Kaleidoscope:- A  Kaleidoscope is an instrument or toy containing inclined plane mirrors which produce multiple reflections of coloured glass pieces (or coloured plastic pieces ) and create beautiful patterns. The Kaleidoscope consists of three long and narrow strips of plane mirrors inclined at 60⁰ to one another forming a hallow prism, and fitted into a cardboard tube .One end of the cardboard tube is closed by an opaque disc(cardboard disc) having a small hole at its centre .The other end of the cardboard tube is closed with two glass disc : the inner disc being of transparent  and the outer disc of translucent. A number of small pieces of different coloured glass (or plastic) and having different shapes are kept between the two  materials which can move around freely in the space between the two discs.

               When we hold the kaleidoscope towards light and look inside it through small hole ,we see beautiful patterns of coloured glass. This all is because  of multiple reflections from inclined plane mirrors.

  Kaleidoscopes are used by designers of wall papers and fabrics, as well as by artists to get ideas for new patterns.

                                                 

 Human Eye: We see things only when light coming from them enters our eyes. Eye is one of our most important sense organs.

The eye has a roughly spherical shape. Outer coat of the eye is white. It is tough so that it can protect the interior of the eye from accidents. Its transparent front part is called cornea. Behind the cornea, we find a dark muscular structure called iris. In the iris, there is a small opening called the pupil. The size of the pupil is controlled by the iris. The iris is the part of the eye which gives it its distinctive colour. When we say that a person has green eyes, we refer actually to the colour of the iris. The iris controls the amount of light entering into the eye.

                                       

 

Behind the pupil of the eye is a convex lens which is thicker in the centre. The lens focuses light on the back of the eye, on a layer called retina. Retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve.

There are two kinds of cells

(i) Cones, which are sensitive to bright light. Cones also cause the sensation of colour of objects in our eyes.  and

 (ii) Rods, which are sensitive to dim light. At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot.

PERSISTENCE OF VISION:- The impression of an image does not vanish immediately from the retina. It persists there for about 1/16th of a second.The ability of an eye to continue to see the image of an object for a very short duration even after the object has disappeared from the view is called persistence of vision. So, if still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives this object as moving.

Care of Eyes:

1.      It is necessary that we take proper care of our eyes. If there is any problem we should go to an eye specialist. Have a regular checkup. If advised, use suitable spectacles.

2.      Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too much light, like that of the sun, a powerful lamp or a laser torch can injure the retina. Do not look at the sun or a powerful light directly.

3.      Never rub eyes. If particles of dust go into eyes, wash eyes with clean water. If there is no improvement go to a doctor. Wash eyes frequently with clean water.

4.      Always read at the normal distance for vision. Do not read by bringing book too close to eyes or keeping it too far.

5.      Lack of vitamin A in foodstuff is responsible for many eye troubles. Most common amongst them is night blindness.

6.      One should, therefore, include in the diet components which have vitamin A. Raw carrots, broccoli and green vegetables (such as spinach) and cod-liver oil are rich in vitamin A. Eggs, milk, curd, cheese, butter and fruits such as papaya and mango are also rich in vitamin A.

Visually Challenged Persons Can Read and Write:- Some persons, including children, can be visually handicapped. They have very limited vision to see things. Some persons cannot see at all since birth. Some persons may lose their eyesight because of a disease. Such persons try to identify things by touching and listening to voices more carefully. They develop their other senses more sharply. However, additional resources can enable them to develop their capabilities further.

Braille System: The most popular resource for visually challenged persons is known as Braille. The present system was adopted in 1932. There is Braille code for common languages, mathematics and scientific notation. Many Indian languages can be read using the Braille system. Visually challenged people learn the Braille system by beginning with letters, then special characters and letter combinations. Methods depend upon recognition by touching. Each character has to be memorized. Braille texts can be produced by hand or by machine. Type writer - like devices and printing machines have now been developed.

 

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TEXTUAL QUESTIONS

Q1.

Answer:- If we are in a dark room, then it is not possible for us to see objects in the room. However, objects outside the room are visible to us. An object becomes visible when light reaches our eye after being reflected from the object. If there is no light in the room, then the objects inside the room cannot reflect any light. Hence, we cannot see in a dark room. If there is light present outside the room, then we can see the objects outside the room.

Q2.

Answer:- Regular reflection takes place from a smooth or a regular surface. In regular reflection, all reflected rays are parallel to each other for parallel incident rays. Irregular or diffused reflection takes place from an irregular surface. In diffused reflection, the reflected rays are not parallel to each other for parallel incident rays. This happens because of the presence of irregular microscopic surfaces. Hence, parallel incident rays reflect in different directions. However, each ray obeys the laws of reflection. Therefore, laws of reflections are not violated in diffused or irregular reflections.

Q3.

Answer:-  (a) Polished wooden table → Regular reflection                                                                                       A polished surface is an example of a smooth surface. A polished wooden table has a smooth surface. Hence, reflections from the polished table will be regular.

(b) Chalk powder → Diffused reflection                                                                                                                   Chalk power spread on a surface is an example of an irregular surface. It is not smooth. Therefore, diffused reflection will take place from chalk powder.

(c) Cardboard surface → Diffused reflection                                                                                                                        Cardboard surface is also an example of an irregular surface. Hence, diffused reflection will take place from a cardboard surface.

(d) Marble floor with water spread over it → Regular reflection                                                                               Marble floor with water spread over it is an example of a regular surface. This is because water makes the marble surface smooth. Hence, regular reflection will take place from this surface.

(e) Mirror → Regular reflection                                                                                                                                  Mirror has a smooth surface. Therefore, it will give a regular reflection.

(f) Piece of paper → Diffused reflection                                                                                                                    Although a piece of paper may look smooth, but it has many irregularities on its surface. Due to this reason, it will give a diffused reflection.

Q4.

Answer:- Laws of reflection:

(i) The angle of reflection is always equal to the angle of incidence.

(ii) The incident ray, the reflected ray and the normal to the reflective surface at the point of incidence all lie in the same plane.

Q5. 

Answer:- Place a plane mirror on the table. We take a paper sheet and make a small hole in its centre. Make sure that the light in the room is not bright and hold the sheet normal to the table. Take another sheet and place it on the table in contact with the vertical mirror. Draw a normal line on the second sheet from the mirror. Now, light a torch on the mirror through the small hole such that the ray of light falls on the normal at the bottom of the mirror. When the ray from this hole is incident on the mirror, it gets reflected in a certain direction. We can easily observe the incident ray, reflected ray and the normal to the mirror at the point of incidence on the sheet placed on the table. This shows that the incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.

Q6.

Answer:-  (a) A person 1 m in front of a plane mirror seems to be __2 __ m away from his image.

(Object distance and image distance are the same from a plane mirror. The image of a person 1 m in front of a mirror is 1 m back to the mirror. Hence, the image is 1 + 1 = 2 m away from the person.)

(b) If you touch your __left__ ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with your _left hand_.

(This is because of lateral inversion of images formed in a plane mirror.)

(c) The size of the pupil becomes __large__ when you see in dim light.

(In dim light, the amount of light entering the eye is very little. To increase the amount of light, the pupil expands.)

(d) Night birds have __less__ cones than rods in their eyes.

(Night birds can see in the night, but not in the day. They have on their retina a large number of rod cells and only a few cones.)

 

Q9.

Answer:- Construction of a kaleidoscope: Three rectangular mirror strips of dimensions 15cm × 4cm (l × b) are joined together to form a prism. This prism is fixed into a circular cardboard tube. The circular cardboard tube should be slightly longer that the prism. This circular tube is now closed at one end with a cardboard disc. This disc has a hole in it through which we can see.At the other end of the circular tube, a plane glass plate is fixed. It is important that this glass plate touches the prism mirrors. On this glass plate, several small and broken pieces of coloured glass are placed. This end is now closed by a round glass plate allowing enough space for the coloured glass pieces to move

 

Q10.   

Answer:-

                                

Q11.

Answer:- Laser light is harmful for the human eyes, because its intensity is very high. It can cause damage to the retina and lead to blindness. Hence, it is advisable not to look at a laser beam directly.

Q12.

Answer:- To protect our eyes, the given points should be taken into account:

(i) Visit an eye specialist regularly.

(ii) Avoid reading in dim light and very bright light.

(iii) Avoid direct exposure of sunlight to the eye.

(iv) Clean your eyes with cold water quickly if dust particles or small insects enter your eye. Do not rub your eyes.

(v) Maintain a distance of at least 25 cm between the book and your eyes while reading.Q13.

Answer:-  If the reflected ray is at an angle of 90° to the incident ray, then the angle of incidence is 45 °. According to the law of reflection, the angle of incidence is equal to the angle of reflection. Therefore, the angle of incidence and the angle of reflection both are 90⁰/2= 45°.

Q14.

Answer:- Infinite or multiple images of the candle will be formed because of multiple reflections between the mirrors. When two mirrors are placed parallel to each other, then infinite number of images are formed.

Q15.

Answer:- The first law of reflection is used to obtain the path of reflected light. It can be observed that the given ray of light will reflect from the second mirror at an angle 60°.

Q16.

Answer:- A plane mirror forms a virtual image behind the mirror. The image is as far behind the mirror as the object is in front of it. A cannot see his image because the length of the mirror is too short on his side. However, he can see the objects placed at points P and Q, but cannot see the object placed at point R (as shown in the given figure).

Q17.

Answer:- (a) Image of the object placed at A is formed behind the mirror. The distance of the image from the mirror is equal to the distance of A from the mirror. Image of A is shown in the given figure.

(b) Yes. Paheli at B can see this image.

(c) Yes. Boojho at C can see this image.

(d) Image of the object at A will not move. It will remain at the same position when Paheli moves from B to C.

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 POLLUTION OF AIR & WATER     

                                                                                                            

Composition of Air:Earth's atmosphere is 78% nitrogen, 21% oxygen, 0.9% argon, and 0.03% carbon dioxide with very small percentages of other elements. Our atmosphere also contains water vapor. In addition, Earth's atmosphere contains traces of dust particles, pollen, plant grains and other solid particles.

i.e.Nitrogen (N₂): 78.09%, Oxygen (O₂): 20.95%, Argon (Ar): 0.93%, Carbon dioxide (CO₂): 0.038%, Others (less than 0.002% each): Neon (Ne), Helium (He), Krypton (Kr), Hydrogen (H₂), Xenon (Xe). 

 

Air Pollution: The contamination of air by the addition of unwanted and toxic substances like dust smoke etc. which have harmful effects on both living and non-living things is called air pollution. The substances which contaminate the air are called as air pollutants. e.g. smoke, dust, carbon dioxide, carbon monoxide nitrogen oxide, chlorofluorocarbons (CFCs) etc.                                                                     Air pollutants are particulate pollutants and the gaseous pollutants. Particulate pollutants include dust particles, soot, aerosol and smoke. Gaseous pollutants include carbon monoxide, nitrogen dioxides, hydrogen sulphide.

 

Causes of air pollution:  the various causes of air pollution are

1.      Cars, trucks, jet airplanes and other combustion engine vehicles cause air pollution by releasing the harmful gases like carbon monoxide, nitrous oxide and gaseous oxide.

2.      Factories, office buildings, homes and power-generating stations burn fossil fuels, which cause air pollution.

3.      Petroleum refineries release hydrocarbons and various particulates that pollute the air.

4.      Pesticides used to kill indoor and outdoor pests, insecticides used to kill insects and herbicides use to kill weeds all cause air pollution.

5.      Radioactive fallout causes air pollution from the nuclear energy dispersed, which is a dust.

6.      Dust from fertilizers used to help plants grow causes air pollution.

7.      Mining causes air pollution by releasing a variety of particles.

8.      Mills and plants, include paper mills, chemical plants, iron mills, steel mills, cement plants and asphalt plants, release emissions into the air causing air pollution.

9.      Natural volcanic eruption also add certain gases, volcanic dust etc. to the air to pollute it.

 

Smog: The mixture of particulates with gaseous oxides of sulphur present in atmosphere is called smog. The principal source of smog is the combustion of industrial and household fuels (coal and petroleum). Because of the presence of SO₂ and carbon (soot) particles, smog has a reducing character. It occurs in winter months particularly in early morning hours. It causes severe lung and throat irritation.

 

Harmful effects of smog:  The harmful effects of smog are

i.        Smog causes respiratory problems like asthma attacks, bronchitis, heart related disorders.

ii.      Being noxious, it causes irritation to eyes, throat and nose.

iii.    It reduces visibility and affects road as well as air traffic.

iv.     It damages plants; Ozone is very toxic to leafy vegetation such as tomatoes, tobacco and grape plantation. Ozone also damages old growth forests closer to sea level. Small animals incur respiratory and other health stress disorders.

v.       Other materials like electronic and electrical equipments get affected.

vi.     Extreme and unexpected conditions due to smog have caused death.

 

Acid rain: Acid rain is an effect of air pollution. The acid rain is caused when sulphur dioxide and nitrogen oxides from the burning of fossil fuels such as, petrol, diesel, and coal combine with water vapour in the atmosphere and fall as rain, snow or fog. These gases can also be emitted from natural sources like volcanoes. Acid rain causes extensive damage to water, forest, soil resources and even human health.

 

 

 

 

Harmful effects of acid rain:

i.        Acid rain chemically strips waterways of necessary nutrients and lowers the pH to levels where plants and animals cannot live.

ii.      Acidic rain damages the bark and leaves of trees and harms the fine root hairs of many plants which are needed to absorb water.

iii.    Metallic surfaces exposed to acid rain are easily corroded.

iv.     Textile fabrics, paper and leather products lose their material strength or disintegrate by acid rain.

v.       Building materials such as limestone, marble, dolomite, mortar and slate are weakened on reaction with acid rains because of the formation of soluble compounds.Thus, acid rain is dangerous for historical monuments.

 

Greenhouse effect: The Greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (referred to as greenhouse gases), trap energy from the Sun. Without these gases heat would escape back into space and living on Earth would be inhospitable with average temperature being about 60 F lower. Because of the way they warm our world these gases are referred to as greenhouse gases.

Some greenhouse gases occur naturally, while others result from human activity. The various natural greenhouse gases are: water vapor, carbon dioxide, nitrous oxide, ozone and methane. Carbon dioxide, methane and nitrous oxide, levels in the atmosphere are added by human activities of industry, transport, agriculture, organic and solid waste combustion. Very powerful greenhouse gases that are not naturally occurring include hydroflurocarbons (HFCs) perflurocarbons (PFCs) and sulphur hexafluroide (SF₆), which are generated in a variety of industrial processes.

 

Global warming:  The process of increase in the level of greenhouse gases in the atmosphere is the global warming which is the major environmental issues. The temperature of the earth is increased in the level of 0.6⁰ C. The control of global warming are,

    1)   Reducing deforestation

    2)   Planting more trees

    3)   Slowing down the growth of greenhouse gases into atmosphere

    4)   Improving the efficiency of energy usage

    5)   Cutting down use of fossil fuel

 

Harmful effects of global warming:The various harmful effects of global warming are

i.              Warming of oceans will result to rise in sea level. Melting of glacier ice will also occur, that causes further rise in sea level.

ii.            Seasonal changes will be longer in some areas.

iii.          The warm world will be more humid and the rainfall will be increased greater humidity.

iv.          Storms may occur frequently and also become intense too.

v.            This also causes dryness in some parts of the world.

vi.          The pattern of wind blowing may be harder and also differs.

vii.        Weather conditions would be predicable in less and more extreme.

viii.      Crops and forests may be affected by more insects and plant diseases.

ix.          Changing environment will affect plants and animals. Animals migration will happen.

x.            Some of the forests types may get disappear.

xi.          This kind of heat stress will lead to death of more people or get sick.

xii.        Malaria, dengue fever, yellow fever and encephalitis will spread to other parts of the world, they are the tropical diseases.

 

Control of air pollution:In order to control air pollution following measures are being taken:-

i.                    Automobiles should be treated with catalyst to cut down CO emissions.

ii.                  Substituted bio-fuels should be utilized to cut down the harmful emissions.

iii.                To prevent the increasing concentrations of CO2 in the atmosphere forests are being developed and stress is given ongoing green everywhere and recycling.

iv.                 Nitrogen oxides are also now being converted into N2 by use of catalyst in fuels.

v.                   Scrubbers are being used to remove sulphur oxides introduced in air.

vi.                 Alternative sources of energy are being used in place of thermal power plants using burning of coal, like hydroelectric and nuclear power plants.

vii.               Methods are being employed to reduce the presence of Carbon and other particulates in the atmosphere.

 

Water pollution: Water pollution is the change or alteration caused to the natural water resources due to the release of pollutants in it. Major water bodies like sea, rivers, lakes, ponds, and ocean and also the underground is affected due to water pollution. The major causes for the water pollution is release of industrial wastes and sewage into the water bodies, excess fertilizers and other chemicals washed away from the land and mixing with water, releases of oil and other non-soluble substances in water, fecal release in water, etc. Conclusion about pollution of water is it affects the life of aquatic plants and animals, eutrophication, land plants as water is required for their survival, bio-magnifications, and causes several diseases in animals and human beings.

 

Causes of Water Pollution: There are several causes of water pollution which are as follows: 

i.               In urban areas, the wastewater sewerage etc. is let out untreated and causes large scale water pollution.

ii.            Most of the rivers and other sources of fresh water are polluted by industrial wastes or effluents.

iii.          Traces of fertilizers and pesticides are wasted into the nearest water bodies at the onset of the monsoons or whenever there are heavy showers.

iv.          Intensive and ever increasing usage of chemical fertilizers, pesticides, and other chemicals cause water pollution.

v.            Flood-plain cultivation is another significant contributor to water pollution.

vi.          Religious faiths and social practices also add to pollution of river waters.

vii.        Carcasses of cattle and other animals are disposed in the rivers.

viii.       Mass bathing in the river during religious festival is another environmentally harmful practice.

ix.          Plastic bags are also very dangerous and further add to the pollution load to the river water.

 

Sources of Water Pollution: The various sources of water pollution are: Factories, Refineries, Waste treatment facilities, Mining, Pesticides, herbicides and fertilizers, Human sewage, Oil spills, Failing septic systems, Soap from washing your car, Oil and antifreeze leaking from cars, Household chemicals, and Animal waste.

 

Potable water: Potable water is water which is fit for consumption by humans and other animals. It is also called drinking water, in a reference to its being fit for drinking. Water may be naturally potable, as is the case with pristine springs, or it may need to be treated in order to be safe. In either instance, the safety of water is assessed with tests which look for potentially harmful contaminants.

 

Water purification: Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from raw water. A common method of purifying water and making it fit for drinking constitutes the following steps.

i.        Sedimentation: water from its source is allowed to flow into the sedimentation tanks. It is allowed to stand for a while so that the suspended solid impurities settle down. This process is called as sedimentation. Chemicals like alum may also be added to the water to weigh down the suspended impurities.

ii.      Filtration: After sedimentation water is allowed to flow into a tank containing layers of sand and gravel. This removes the fine particles of impurities from the water and is known as filtration.

iii.    Chlorination: Finally, a little amount of chlorine gas is added to the water. It dissolves and kills any remaining bacteria. This process is called as chlorination. The chlorinated water is then supplied to the nearby areas through pipelines.

iv.     Boiling: The water which we get from the taps is further boiled at the home for drinking purposes which kills all the microorganisms that comes in contact with the water during its supply through pipelines.

 

Ways to Prevent Water Pollution: A few ways to prevent water pollution are

i.        Toxic products like paints, automobile oil, polishes, and cleaning products should not be disposed off in water resources.

ii.      Non-degradable products like tampons, sanitary napkins, and diapers should not be flushed down the toilet to nearby water source.

iii.    We should refrain from throwing litter into streams, lakes, rivers, or seas.

iv.    We should try using environmentally friendly household products like toiletries, soap-based household cleaning material, and washing powder as far as possible.

v.      We should try using natural fertilizers and pesticides as far as possible, or we should not overuse them or over-water gardens and lawns.

vi.    We should prevent leakages of toxic fluids like antifreeze and oils to the water sources.

We should actively conserve water by turning the tap off when we do not need running water, such as while brushing teeth. Apart from preventing water shortages, it lessens the amount of water that needs to be treated.

 

                                                  TEXTUAL QUESTIONS

Q NO 1:-What are the different ways in which water gets contaminated?

ANS:-There are many ways in which water gets contaminated:

1.                  By washing, bathing or other household activities.

2.                  By sewage.

3.                  By toxic chemicals discharged by industries.

4.                  By garbage and dead bodies dumped in water resources.

5.                  By fertilizers, pesticides, insecticides etc.

Q NO 2:-At an individual level, how can you help to reduce air pollution?

ANS:-Air pollution at an individual level can be reduced by taking following steps:

1.              Automobile use is to be reduced.

2.              Burning of leaves, tyres etc must be stopped.

3.              Plant trees around the residential areas.

4.              Use of public transport.

5.              Use of crackers should be stopped.

Q NO 3:-Clear, transparent water is always fit for drinking. Comment?

ANS:-Clear, transparent water may appear clear but it is not pure. It may contain  dissolved impurities and many micro-organisms which may be carrier of diseases. Best way to get pure water is boiling. Boiling kills germs and boiled water can be used for drinking purposes.

Q NO 4:-You are a member of a municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents?

ANS:-List of measures to obtain clean water:

 

1.                  Industrial wastes must be treated before throwing into water sources.

2.                  Sewage must be treated by physical and chemical methods before dumping in water sources.

Q  NO 5:-Write the differences between:

ANS:-The various differences between pure air and polluted air are given below:

 

S. no	PURE AIR	POLLUTED AIR
1.	Pure air is transparent	Polluted air is dirty and translucent
2.	Micro-organisms are absent.	Micro-organisms are present
3.	No smoke and dust particles are seen.	Smoke and dust particles are in high amount.
4.	No odour is there.	It may have foul smell.

 

Q NO 6:-Explain circumstances leading to acid rain. How does this acid rain affect us?

ANS:-When NO₂, N₂O,SO₂and SO₃  produced from incomplete combustion of fossil fuels and by smelting of non ferrous metals combine with water to form HNO_3, H₂SO₄ and H₂SO₃  and fall down in the form of rain, it is called acid rain. It destroys crops, wild plants, steel rail tracks. It causes irritation of eyes, nose and throat.

 

Q NO 7:-Which of the following is not a green house gas ?

ANS:-Nitrogen

 

Q NO 8:-Describe the ‘green house effect’ in your own words ?

ANS:-Carbon dioxide is present in the atmosphere in the form of very small proportion. It helps in the process of photosynthesis, it also produces the green house effect. The heating of earth due to trapped radiations is called green house effect. Our sun emits light consisting of UV  and infra red radiations, UV radiations are absorbed by ozone layer ,but infra- red radiations pass through   atmosphere and reach the surface of earth .some of the rays are reflected back. The carbon dioxide absorbs these reflected rays . Since, infra-red radiations have a heating effect, the atmosphere gets heated up. The name green house is derived from glass house in which green plants are kept.

 

Q NO 9:-Prepare a brief speech on global warming You have to make in your class. 

ANS:-Global warming as the name suggests is the increase in temperature of the globe, i.e the average temperature of the atmosphere has increased. Few gases like carbon dioxide,methane,NO₂ are responsible for it. The quantity of  these gases is increasing day by day in the atmosphere. If this is not checked in time, the temperature will have a big rise and there will be hazards all around us. Such as, glaciers will melt, low lying area will get submerged in water,  rainfall will be affected, sea level will rise affecting   production of crops, forests etc and it will also affect us, the lifestyle of living organisms. So special and immediate measures are to be taken to stop global warming.

 

Q NO 10:-Describe the threat to the beauty of the Taj Mahal?

ANS:-Taj Mahal is one of the seven wonders of the world. .It is a white building made up of white marble.

The monument is being threatened by air pollution .The area surrounding Taj is congested with many harmful gases such as sulphur dioxide, nitrogen oxides, etc. This  is being emitted by burning of fossil fuels by industries established around the Taj. These gases dissolve in rain water to form acid rain. This acid rain falls on marble, react with it and dissolves and tarnishes it. If no steps are taken to minimize the fall of acid rain, one day marble monument will remain no more and all the marble will get distorted.

 

Q NO 11:-Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

ANS:-With increased quantities of nutrients ( nitrates, phosphates, etc) the algae flourish in the water. When these algae die decomposers decompose them, using oxygen present in water. Thus, there is decrease in oxygen level in water, which affect the survival of aquatic organisms.

 

Q NO 12:-What do you understand by green house effect?

ANS:-Already discussed.

 

  Q NO 13:-Define global warming and name the various gases which lead to global warming?

ANS:-Global Warming: The increase in level of carbon dioxide due to human activities, traps heat radiations and does not allow it to escape into the space resulting in the increase in the temperature of the earth’s atmosphere is called global warming. Gases responsible for global warming are carbon dioxide, methane, nitrogen oxides and water vapours.

 

Q NO 14:-What are the ill effects of global warming?

ANS:-ill effects of global warming are:-

1.                    It can cause the snow on the mountains to melt resulting in dramatic increase in the level of sea water and flooding the low lying areas.

2.                    It can have wide ranging effects on:-

a)       Rainfall patterns.

b)      Agricultural crops.

c)      Human and animal life.

 

Q NO 15:- Define Air pollution ?

ANS:-The contamination of air by undesirable substances which have  harmful effect on both the living and non living things is called air pollution.

 

Q NO 16:- What are air pollutants and name them?

ANS:-The substances which contaminate air are called air pollutants e.g, smoke , dust, CO₂, sulphur dioxide, carbon monoxide , nitrogen oxide , chlorofluoro carbons.

 

QNO 17:-Name the various sources of air pollutants?

ANS:-The various sources of air pollutants are smoke from automobile exhausts, forest fires, dust particles, volcanic eruptions, emissions from factories and industries etc.

 

Q NO 18:-Define smog and what are its ill effects?

ANS:-Smog is a  mixture of smoke and fog. Smoke may contain oxides of nitrogen which combine with other pollutants and fog to form smog.

Smog causes breathing difficulties such as asthama, wheezing in children.

 

Q NO 19:-Name the alternative fuels which we can use instead of fossil fuels?

ANS:-The alternative fuels which can be used instead of fossil fuels are:

1.      Solar energy.

2.      Hydro power

3.      Wind energy.

 

Q NO 20:-What are the factors responsible for pollution of the river?

ANS:-The factors responsible for pollution of the river are:

1. Taking bath, washing clothes and defaecating in the river water.
2. By discharging industrial, chemical waste and dumping toxic materials into the river.
3. By releasing sewage and silt into the river water.
4. By releasing or dumping dead animals into the river water.
5.  Throwing non- biodegradable polythene bags into the river.

 

Q NO 21:- What steps can be taken to restore the river Ganga to its past glory?

ANS:-The following steps that can be taken to restore the river Ganga to its past glory are:

1.  Strict laws should be enacted for checking the indulgence of individuals and Trusts in polluting the water of river Ganga.
2. Some seminars, lectures and religious and social groups should be created for causing awareness among the public about the ill effects of polluting Ganga water.
3. Some social groups should be involved and helped by the government in cleaning  the river.
4. Industries should not be allowed to be installed in the proximity of banks of river Ganga.
5. Industries should be warned not to release wastes directly into the water before it is treated for removing all pollutants.

 

Q NO 23:-What will happen if we drink polluted water?

ANS:-Polluted water may contain bacteria, viruses, fungi and parasites apart from insoluble and soluble impurities. If we drink this polluted water it may cause diseases like cholera, typhoid and jaundice.

 

 

 

Q NO 24:-Name some methods used for purification of water?

ANS:-Methods used for purifying water are :

1. By boiling :- We can purify water by killing the germs present in it by boiling.
2. By chlorination :- It is a chemical method commonly used for purifying water for safe drinking. It is done by adding specified quantity of chlorine tablets or bleaching powder to water. It also kills germs present if any in water.
3. By filtering:- This is a physical method of removing impurities and also kills germs present if any in water.

 

Q NO 25:-What are the common water borne diseases ?

ANS:-The diseases caused by polluted water (containing bacteria, virus, fungi or parasites)  are diarrhea, dysentery, jaundice, vomiting ,cholera and typhoid.

 

Q NO 26:-How would the disposal of garbage etc. affect the living organisms in the river?

ANS:-If the garbage is thrown directly into the river , then the pollution and temperature level rises so high that the aquatic animals and other living organisms  cannot survive. It is because these act as nutrients for the algae to flourish .Once these algae die , they serve as food for bacteria (decomposers) . A lot of oxygen in water gets used up which may kill aquatic animals .

 

Q NO 27:-Why do we need to filter water before drinking?

ANS:-Sometimes water contains insoluble impurities. To make this water fit for drinking there is a need to remove these insoluble impurities by filtering it.

 

Q NO 28:-Where do you get your drinking water from?

ANS:-We get our drinking water from municipal tap which we get after having been filtered and chlorinated thus making it fit for drinking.

 

Q NO 29:-How can you save water?

ANS:-We should not waste water rather we should save it. Our mantra should be reduce, reuse and recycle.

             For this we should use water when it is required and immediately turn off the tap. We can think of reusing water for washing clothes, for watering plants, for washing automobiles and for other household tasks. As for example water used for washing vegetables may be used to water plants in the garden. Sewage treatment plants should be used for recycling water. This would help to save water for future uses.

 TOPIC:-  FRICTION.                                                                                                                                                                                                                                                                                                     

Friction: Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. It may be thought of as the opposite of "slipperiness".i.e. it is an opposing force that comes into play when two surfaces comes in contact...

 

Causes of friction: The main causes of friction are

1.      Fishinmission:- Friction is caused by masses that travel past each other in opposite directions, which forms heat. Adhesion, surface roughness, and deformations cause friction.

2.      Electrosam:- Friction is caused due to relative motion between two surfaces. Surfaces are not perfectly smooth. They have small bumps. These cause the force of opposition during movement called as friction.

 

Types of friction: Friction is of three types, namely Static friction, Dynamic or Kinetic or sliding friction and Limiting friction.

1.      Static Friction: Static Friction is the friction which is produced between two surfaces in contact with each other at the position of rest. This friction is more powerful than any other type of friction. It is most difficult to overcome the static friction because at this position, the irregularities are most effectively pressed against each other. This type of friction needs a lot of energy to overcome.

2.      Dynamic or Kinetic or Sliding Friction: This type of friction arises when two objects in contact are in motion. It is lesser than Static friction. This friction is lesser because the irregularities of both surfaces do not get enough time to get locked with each other as the objects are already in motion.      

3.     Limiting friction: It is the maximum value of static friction which comes into play when a body is just about to slide over the surface of another body. For an applied external force greater than the limiting friction, the body begins to move. Once motion has begun, static friction cannot be considered. A new type of friction called kinetic friction comes into play.

 

Laws of limiting friction

• The direction of limiting frictional force is always opposite the direction of motion.

• Limiting friction acts tangential to the two surfaces in contact.

• The magnitude of limiting friction is directly proportional to the normal reaction between the two surfaces.

• The limiting friction depends upon the material, the nature of the surfaces in contact and their smoothness.

• For any two given surfaces, the magnitude of limiting friction is independent of the shape or the area of the surfaces in contact so long as the normal reaction remains the same.

 

Drag: It is the term used to describe the frictional force which is exerted by the fluids on the bodies moving in it. This friction needs a lot of energy to overcome so, bodies of such objects which move in fluids are streamlined to counter the friction offered by fluids. 

What Causes Friction? The surfaces of bodies are never perfectly smooth. Even a very smooth surface seen under a microscope, is found to have depressions and projections as shown in the figure below. The interlocking of the irregularities of the surfaces in contact causes friction.

 

              

Rolling Friction: Rolling friction is the friction which comes in effect when two bodies are rolling on each other. Rolling movement of both objects don’t allow the locking of irregularities, thus it is the smallest force (friction) of all the three types.

             When a body rolls over a surface, the frictional force developed between the surfaces is called rolling friction. For example, when a wheel rolls over a surface, the surface of the wheel and the surface on which it rolls are both slightly deformed. A resistance to smooth rolling is produced due to this deformation. This resistance or opposing force is called rolling friction. The deformation of a motor car tyre in contact with the road is an example. The tyre becomes slightly flattened at the point of contact with the road and also the surface in front of the tyre or wheel gets slightly raised forming a kind of moving ridge.

Friction due to liquids and gases: Liquids and gases also exert friction. However, friction offered by them is less compared to that offered by solid surfaces.                                      

         The best example to demonstrate the friction offered by air is the meteor shower. Each time a comet passes the Sun it loses some of its gas and ultimately only the dust particles and bits of rocks are left in space. When these particles enter earth's atmosphere, they burn due to the heat produced by air resistance and produce a shower of meteors or shooting stars.

The friction due to water is much less than that between solid surfaces and hence it is difficult to stop ships or boats. To stop a ship the engine is fired in the opposite direction.

 

How can friction be decreased?

The friction can be decreased by the following methods

i.              It can be reduced by using lubricants like oil, grease and graphite Powder.

ii.           It can be reduced by using ball bearings or roller bearings.

iii.         It can be reduced by using anti-friction metals or alloys.

iv.         It can be reduced by separating the surfaces by an air cushion.

v.            It can be reduced by streamlining the body. Aeroplanes, boats and paper rockets are examples of streamlined objects.

vi.          It can be reduced by polishing the surfaces the friction between the moving surfaces can be reduced.

 

How can friction be increased? The friction can be decreased by the following methods

i.              By making both the surfaces very rough.

ii.            By making irregular projections and depressions like those we see on the tyres.

Advantages of Friction

1. Due to friction we are able to walk on the surface of the Earth.

       ii.            The brakes applied in automobiles work only due to friction.

     iii.            Nails, screws and the wooden boards are held together due to force of friction.

     iv.            The fibres of thread are held together due to force of friction.

Disadvantages of Force of Friction

1. In overcoming the friction, a lot of energy is wasted in the form of heat. Friction causes wear and tear of the moving parts.

       ii.            Due to friction, speed of automobiles cannot be increased beyond a certain limit.

Friction is a necessary evil: Friction is the retarding force which is called into play when a body actually moves or tends to move over the surface of another body. Frictional forces always oppose relative motion and never help it. Even when no relative motion is actually present but there is only a tendency for relative motion, frictional force exists between surfaces. For Example, without friction between our feet and the ground. It will not be possible to walk. Any time you want to move an object, friction can make the job for more difficult. Friction can make it difficult to slide a box across the floor, or ride a bicycle or walk through deep snow

            In short, life is impossible without friction - It would be impossible to climb, to fix a nail, to drive a car if there were no friction. The tyres of the vehicle are made rough to increase friction. Various parts of a machine are able to rotate due to friction between belt and pulley.

Friction is an Evil: Friction is an evil due to following reasons.

i.           Wear and Tear of the machinery is due to friction.

ii.         Friction between different parts of the rotating machines produce heat and causes damage to them.

iii.       We have to apply extra power to machines in order to overcome friction. Thus the efficiency of the machines decreases.

Factors of friction: The frictional force depends on the following factors -

i.                    It depends on the nature of the surface.

ii.                  It depends on the smoothness of the surface.

iii.                It depends on the hardness with which two surfaces in contact are pressed against each other.

 

 

TEXTUAL QUESTIONS

A. Answer the following questions.

Q NO 1:-Why are the worn out tyres discarded?

ANS:-The worn out tyres from which grooves have disappeared are discarded, as they slip on the roads and don’t offer required amount of friction.

Q NO 2:-Why do carom coins move fast on carom board when dusted with talcum powder?

ANS:-When talcum powder is dusted on the surface of carom board it fills the irregularities and makes the surface smoother, thus reducing friction resulting in the fast movement of carom coins.

Q NO 3:-Why is the surface of conveyor belt made rough?

ANS:-The surface of conveyor belt used for turning wheel and pulleys in factories is made rough so that they could provide the necessary reaction due to friction and the wheels could turn about the axles.

Q NO 4:-Why is the sewing machine  often oiled?

ANS:-The oil is used as a lubricant in wheels , separating the two surfaces so that the interlocking of irregularities gets reduced as the spaces are filled with the oil. This makes the various parts of sewing machine to move faster and smoothly.

Q NO 5:-Why do new automobile tyres have deep grooves?

ANS:-It is because there must be a friction between the tyres of an automobile and the road. It is for the same reason that special kind of grooves are made in tyres so that they offer the required amount of friction.

Q NO 6:-Why does a ball rolling on the ground slow down?

ANS:-When a ball rolls on ground it is acted upon by two forces

a. Force of friction which comes into play due to irregularities of one  interlocking into the other surface and thus offering friction and opposing the movement of ball and

b.The resistance of air .

These two forces together make the ball to slow down.

 

 

 

Q NO 7:-Why are the boats and aeroplanes given special shape?

ANS:-The boats and aeroplanes are given special shape i.e.they are streamlined.The special shape of the boat or aeroplane around which water or air can flow easily, offers minimum amount of friction and resistance. This helps them for their free and easy movement.

 

Q NO 8:-Why do meteors burn on entering into the atmosphere?

ANS:-The meteors(shooting stars) enter the atmosphere at very high speed .At such high speed the friction due to resistance of air is very high which results in raising the temperature of meteors to such a high temperature that they catch fire.

 

Q NO 9:-Why do painters use sand papers in polishing doors?

ANS:-The painters use sand papers to break the projections on the surface of wood so as to have a surface which would have minimum friction.

 

Q NO 10:-Why is it easier to tie a knot with cotton string as compared to silk string?

ANS:- We can tie knot only when the material offers some friction. In case of cotton thread the friction is much more than in case of silk thread. So the knot can be tied easily in cotton thread.

 

Q NO 11:-Fill in the blanks.

1.Friction always acts in the direction opposite to the direction of applied force.

2.Static friction is a self adjusting force.

3.Friction is very useful as it helps in the movement of the bodies.

4.Thesliding friction is 10 times the rolling friction.

5.The boats and aeroplanes are streamlined so as to reduce fluid friction.

 

Q NO 12:-Statements given below are incorrect write the correct form.

1.Sliding friction is slightly more than the limiting friction.

ANS:-Sliding friction is slightly less than the limiting friction.

2.The conveyor belts are made rough, in order to decrease friction.

ANS:-The conveyor belts are made rough in order to increase the friction .

3.The friction between two surfaces decreases with the increase in the weight of a body.

ANS:-The friction between two surfaces increases with the increase in weight of a body.

4.The friction offered by the wheels is called sliding friction.

ANS:-The friction offered by the wheels is called rolling friction.

5.The friction increase with the increase in the area of contact at the two surfaces.

ANS:-Friction  remains constant with the increase in the area of contact at the two surfaces.

 

Q NO 13:-What do you understand by the term friction .explain how is it caused?

ANS:-Friction is an opposing force which comes into play when two surfaces comes in contact with each other and try to move relative to one another.

When one body moves over the surface of another body the projections of one fit into the cavities of other surface thus getting interlocked. When force is applied on one body to slide it upon another body, its interlocked irregularities oppose the applied force which appears as friction.

 

 

 

 

 

 

Q NO 14:-Distinguish between the static friction and dynamic friction.

ANS:-

STATIC FRICTION	DYNAMIC FRICTION
1.The force of friction which comes into play when two bodies don’t slide upon one another is called static friction.   2. It is a self - adjusting force to prevent the motion.	1.The force of friction that comes into play when the two bodies are sliding upon one another with a uniform speed is called dynamic friction. 2.It is not a self - adjusting force and does not prevent the motion.

 

Q NO 15:-What is limiting friction ? State laws of limiting friction.

ANS:-The maximum static force of friction which comes into play when one body just slides upon another body is called limiting friction.

Laws of limiting friction.

1.      Limiting friction always opposes the motion of a body and acts in a direction opposite to the direction of applied force.

2.      Limiting friction depends upon nature of two surfaces in contact with each other.

3.      Limiting friction increases with the increase in weight of body and decreases when the weight of the body decreases.

4.      Limiting friction is independent of the area of contact between the two surfaces, provided the weight of the body and nature of the body do not change.

 

Q NO 16:-How is rolling friction caused?

ANS:-The lower surface of the roller or the wheel gets deformed due to the weight of the rolling object causing depression at the point of contact. Because of this deformation of the wheel or roller, a kind of inclined plane is formed. Thus a force is required to cross over continuously rising inclined plane in the direction of motion. This force applied against the continuously forward moving inclined plane is equivalent to the rolling friction.

 

Q NO 17:-Under what conditions the rolling friction increases ?

ANS:-The greater depression formed on the surface in contact with  the rolling object ,the greater is the force of rolling friction.

 

Q NO 18:-State one way of increasing the friction between two surfaces ?

ANS:-Force of friction between two surfaces in contact can be increased by making the surfaces rough. This can be done in many ways .One such method is making grooves in the surfaces so that when they move over each other, the projections of one surface fit into the depressions of the other surface thus making them to interlock.

 

Q NO 19:-Name four ways by which friction can be reduced between two surfaces in contact.

ANS:-Following are the ways by which friction can be reduced between two surfaces in contact:-

1.      By use of lubricants.

2        By using soap solutions.

3        By polishing

4        By streamlining.

 

 

 

Q NO 20:-State two advantages of friction.

ANS:-1.There must be friction between the tyres of an automobile and the road .In    

              the absence of friction there would be slipping and skidding of tyres.

2.Spikes (nails) are provided in the shoes of athletes to increase friction and    

    thus prevent them for slipping.

 

Q NO 21:-State two disadvantages of friction.

ANS:- 1.Friction reduces the speed of moving object to a greater extent.

      2.Friction causes wear and tear to make machines not workable.

 

Q NO 22:-Why is friction called a necessary evil?

ANS:-Friction is a necessary evil, because it reduces the efficiency of the work done (usually by converting most of the energy into heat energy) but at the same time it is also very useful in our life. We are able to walk just because of friction.

 

Q NO 23:-What is a lubricant?

ANS:-A lubricant is a substance which when applied between the two surfaces in contact, reduces the force of friction between them.

a.      How does a lubricant reduce friction?

ANS:-A lubricant separates  the two surfaces  in such a way that the  interlocking of irregularities are much  more reduced as the cavities between them are filled with the lubricant.

C. What kind of lubricant is used in

i. sewing machine

ANS:-Less viscous oil.

ii. The axle of a tractor

ANS:-Grease or more viscous oil.

 

Q NO 24:-Name two solid lubricants and state where they are used.

ANS:-The two solid lubricants are Graphite and fine powder.

          GRAPHITE:-Graphite for heavy parts of machine where oil cannot be applied.                

          FINE POWDER:-On the carrom board so as to reduce friction between the   

          carrom board and the coin.

 

Q NO 25:-What do you understand by term streamlining? Name a few machines which use streamlining to reduce friction?

ANS:- Giving a special shape or design to the bodies so that they offer the least resistance (friction) to the air or water is called streamlining. e.g. of few machines using streamlining to reduce friction are boats, aircrafts, ships and cars etc.

 

Q NO 26:-Why is friction called a perverse force?

ANS:-Friction always opposes the relative motion between any two bodies in contact. Therefore, an extra energy has to be spent in overcoming  friction. Thus it involves unnecessary expense of energy. That is the reason friction is a perverse force.

 

Stars And The Solar System

Celestial bodies: The natural objects which are located outside of Earth's atmosphere in the space, such as the Moon, the Sun,  asteroids, planets, or  stars are called as celestial bodies or heavenly bodies.

 

 Universe: The vast unimaginable surrounding space is known as universe. The universe includes everything that exists, all the stars, planets, satellites and interstellar dust and gases. The earth on which we live is also included in the universe with every living and non-living thing that exists on the earth.

                                                    

 Astronomy: The scientific study of the universe and of objects which exist naturally in space, such as the moon, the sun, planets and stars is known as astronomy. People who study the universe are called astronomers.

 

Light year:  A light year is defined as the distance travelled by the light in one year at the rate of 3 x 10⁵

(i.e.300000) kilometers per second.                                                                                                   i.e. Speed of light = 3 x 10⁵ Km/s

Number of seconds in one year = 1x 365 x 24 x 60 x 60 seconds                                                       Therefore, 1 light year = 3 x 10⁵ x 1x 365 x 24 x 60 x 60 km                                           1 light year = 9.46 x 10¹² kilometers     

 

Light minute:      A light minute is defined as the distance travelled by the light in one minute at the rate of 3 x 10⁵ (i.e.300000) kilometers per second.                                   i.e.          Speed of light =        3 x 10⁵ Km/s                                        Number of seconds in one minute = 1x 60 seconds                                                Therefore, 1 light minute =       3 x 10⁵ x 1x 60 kilometers                                                    1 light minute=        18,000,000 = 18 x 10⁶ kilometers

 

Parsec: Parsec is also a unit of stellar distances frequently used in place of light year. One parsec is equal to 3.26 light years.                                                                                        i.e.     1 parsec =      3.26 light year                                                                                                      =      3.26 x 9.46 x 10¹² kilometers                                          

 

Stars: Stars are the heavenly bodies that are extremely hot and incandescent (i.e. they have their own light). Stars are in reality huge glowing balls of hot gases and are mainly made up of hydrogen. They contain some helium and dust.

Galaxy: A galaxy is a bunch or cluster of enormous stars held together by gravitation. There are about 100 billion galaxies in the universe and each galaxy on an average contains about a hundred billion (10¹¹) stars. Galaxies are of elliptical, spiral and irregular shapes. The galaxy to which our solar system belongs is known as Milky Way or Akash ganga. It is spiral in shape.

 

Constellations:  A group of stars which is arranged in some pattern resembling some recognizable figure is called a constellation. There are about 88 constellations known to us. Some of the important constellations are.­­

i.                    Orion (or hunter) – Vyadha or Mirga.

ii.                  Ursa major (or grater bear) – Saptarishi.

iii.                Ursa minor (or little bear) – Laugh Saptarishi.

iv.               Pleads – Kruttika.

v.                 Scorpio – Vrishchika.

vi.               Cassiopeia – Sarmishtha.

 

Solar system: The system in which nine planets, their satellites and thousands of other smaller heavenly bodies such as asteroids, comets and meteors revolve around the sun is called solar system or solar family. The nine planets that include solar system according to their distance from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

 

Planets:  Planets are the heavenly bodies which revolve around the sun in elliptical orbits. They do not have their own light. They shine on falling of sunlight on their surface. They are made of rocks and metals. The Jupiter is the largest planet with greatest number of moons (i.e. 12) around it and mercury is the smallest planet of solar system.

1.     Mercurry (Budha) – smallest planet and nearest to sun.

2.     Venus (shukra)

3.     Earth (Prithvi)

4.     Mars (Mangal)

5.     Jupiter (Brihaspati) – Biggest Planet.

6.     Saturn (Shai)

7.     Uranus (Indra)

8.     Neptune (Varun)

9.     Pluto (Yama) – It is the farthest planet from the sun.

 

Satellites (or Moons):  A satellite is a solid heavenly body that revolves round a planet. The moon is the natural satellite of the planet earth. The planets Jupiter has 12 satellites or moons, Saturn 21, Uranus 5, mars 2, Neptune 2and earth 1 natural satellites.

 

Asteroids: The assorted debris present between the orbits of mars and Jupiter are called as asteroids which somehow failed to assemble in the form of a planet. So they are sometimes termed as minor planets or planetoids.

 

Comets: A comet is a collection of gases and dust which appears as a bright ball in the sky with a long glowing tail gases include ammonia and methane also. The tail of comets always points away from the sun. The period of revolution of comets around the sun is very large. Holly’s comet was seen in 1996 after a period of 16 years.

 

Meteors (shooting star): The heavenly bodies in the sky which are seen as the bright streaks of light passing across the sky are called as meteors. They are also called as shooting stars, actually they are not but stars but pieces of dust and metal.

 

Meteorites: Meteor which does not burn completely on entering the earth’s atmosphere and strikes the surface of earth is called as meteorite. Size of meteorites varies from a size of a pebble to big blocks having weight in tones. They are mainly composed of metal and rocks.

 

How are meteorites dated?

Radiometric dating technique is used to find the age of solar system, earth and meteorites falling on the earth. Meteorites falling on the earth contain uranium (a radioactive element) that changes to lead by radioactive decay. Half-life of ²³⁸U₉₂ is 4.5 x109 years. By calculating the ratio of ²³⁸U₉₂ and ²⁰⁸Pb₈₂ we can calculate the age of the rocks present in the meteorite.

 

Difference between a star and a planet:

Star	Planet
1.      A star has its own heat and light. 2.      Stars twinkle at night. 3.      Stars are very big in size. 4.      Stars are stationary and do not change their position. 5.      Stars appear to make from east to west. 6.      A star is a huge mass of extremely hot gases. 7.      Stars are countless in number.	1.      A planet has no light of its own but reflects light of sun. 2.      Planets do not twinkle at all. 3.      Planets are smaller in size as compared to stars. 4.      Planets revolve round te sun constantly. 5.      Planets move from west to east 6.      A planet is made up of rocks and metals. 7.      There are nine major planets in our solar system.

 

The Sun: The sun is the nearest star of our earth. It is the star round which the earth and other planets of our solar system revolve. In a way we can say that sun is the head of the solar system. Compared with millions of the sun is a medium sized star and of average brightness. The sun appears to be larger and brighter because it is much nearer to the earth than any other star. The diameter of the sun is 1400000 km (approx.) which is 109 times the diameter of the earth. Therefore sun is about 300000 times heavier than the earth.

 

Difference between a star and a shooting star

Star	Shooting Star (Meteorite)
1.      The materials of the stars mostly consist of hydrogen and helium. 2.      Stars produce heat energy and light energy dueto the fusion of hydrogen. 3.      Stars are extremely big. 4.      Stars last for billions of years.	1.      The material f a shooting star is mostly made of rocks, metals and dust. 2.      The shooting stars produce heat energy and light energy due to the friction of the earth’s atmosphere. 3.      The shooting stars are very small pieces of rocks.

 

Pole star: a star in line with the north pole of the earth whose position does not change is known as a pole star.

 

Phases of the moon: The Waxing and the waning of the disc of the moon as revolves around the earth are known as the phases of the moon.

                                    

                                     TEXTUAL QUESTIONS

Q NO 1:-Fill ups                                                                                                               (i).The branch of science which deals with the study of  Universe is  called   

     astronomy.

(ii).The unburnt part of a meteor which reaches the earth is called meteorite.

(III).The heavenly bodies which revolve around the sun are called planets

(IV).The heavenly bodies  which revolve around the planets are called  

       satellites(moon).

(V).The orbit of  Pluto is not in the same plane as that of the other planets.

(VI).A heavenly body with a long tail, moving around the sun in elliptical path is  

       called comet.

(VII).In the core of the sun, hydrogen gas fuses with the liberation of the energy.

(VIII).A group of stars which resembles an animal or some other known object is  

         called constellation.

Q NO 2:-Statements given below are incorrect. Write correct statements.

ANS:-    1. Halley’s Comet visits our solar system after 76 years.

         2. Hydrogen gas constitutes most of the atmosphere of the sun and the   

             stars.

         3. Alpha centauri is the star nearest to our solar system.

         4. Astronomers have divided the sky into 88 constellations.

         5. Meteors on burning leave behind dust and light.

         6. The orbit of Pluto is different from the orbits of other planets in the   

             solar system

         7. Venus is the second planet nearest to the sun.

         8. Moon revolves round the earth in 27¹/₃ days.

Q NO 3:- Answer the following questions.

 (I).What is universe? Name six different kinds of heavenly bodies found in the  

       universe.

 ANS:- It is the vast un- imaginable space which has in it distant stars, planets   

           and all other things that exist. Heavenly bodies of the universe are:

1.    Moon

2.    Planets

3.    Sun

4.    Stars

5.    Meteors

6.    Comets.

 (II).With reference to the average distance from the sun , state :

a)    The serial number of the planet earth.

ANS:- Earth= 3.

b)   The average distance of the earth from the sun?

ANS:- Average distance of earth from sun is 1496 million km.

c)    The time in which the sunlight reaches the earth.

ANS:-Speed of light = 3 x 10 ⁵ km/ sec

        Distance of earth from the sun = 1.5 x 10⁸ km(approx)

        time taken =  distance covered     = 1.5 x 10⁸ / 3 x 10⁵

                                   Speed of light

             =   ½ x 10³ =   500 sec  

        =   500/60min  = 8.33 min.

 

 a) Name the natural satellite of the earth.

Ans: Natural satellite of earth is moon.

b)   In how many days does this satellite rotate around its own axis?

Ans: The time taken by moon to revolve round its own axis is 27¹/3  days .

c)    In how many days does this satellite complete one revolution around the earth?

Ans: Time taken by moon to revolve around earth is 27¹/3 days.

d)   How is the gravity of this satellite compared with that of earth?

Ans: The gravitational pull of the moon is 1/6^th of that of earth .

e)   State the maximum temperature on the day side and minimum temperature on the night side of this satellite?

Ans: Maximum temperature on the day side of the moon = 110⁰ C.

        Minimum temperature on the night side of the moon = - 150⁰ C. 

iv .What do you understand by the following terms:-

a)    New moon :-

A new moon occurs when the moon is between the earth and the sun , the near side of the moon is dark side. The moon cannot be seen and we call this new moon .

b) Full moon:-

A full moon occurs when the moon is on the far side of the earth from the sun. When the earth is between the sun and the moon, the near side is the light side. We call this full moon.

v)  a: Define solar system.

Ans: The sun along with the eight  planets and their moons constitute the solar system.

b)   Name all the planets in the solar system in the order of their distance from the sun?

ANS:- 1. Mercury   2) Venus    3) Earth   4) Mars   5) Jupiter   6)  Saturn

         7) Uranus     8) Neptune .

vi) a: How many moons mars have?

ANS:- Two moons.

c)    Write the names of these moons.

ANS:- Photos and Deimos.

vii) What is comet? Why does a comet develop a tail while approaching the sun?

ANS:- The bright ‘star like ‘ objects with a long tail , approaching the sun in a highly elliptical orbit are called comets. Because of the pressure of solar radiation ,the tail of the comet consisting of gaseous matter always points away from the sun.

c)  What is a star? What makes the star to give out vast amount of energy?

ANS:-Stars are huge glowing balls of hot gases mainly hydrogen. They also contain some helium and dust. In the stars deep in their cores hydrogen atoms fuse together to form helium atoms and a large amount of nuclear energy in the form of heat and light is liberated. The changes in the life of stars is very slow as compared to our own life. In this universe there are millions of stars of different ages. Stars life span is billion of years. Stars are classified according to their brightness, temperature, colour and size.

d) 1. How are meteors different from stars?

S. no	Star	Meteor (shooting star)
1.	Stars mostly consist of hydrogen and helium.	Meteors are mostly made of rocks, metals and dust.
2.	Stars produce heat and light due to fusion of hydrogen into helium.	Meteors produce heat and light energy due to friction of air when they enter the atmosphere.
3.	Stars are very bright and big in size.	Meteors are very small pieces of rocks. They may also be as small as dust particles.
4.	Stars life span is billions of years.	Meteors last for short period (a few seconds) of time.

 

2. How are meteors different from meteorites?

ANS:-Meteors:-Meteors are the rocky pieces of planets which exploded and broke up long ago and are now seen floating in space. As soon as they enter the atmosphere, they catch fire due to the heat of friction between air and the rocky pieces. These burning pieces move with great speed and look like streaks of  light and are known as meteors. Most of the meteors burn up completely before they fall on the surface of the earth.

Meteorites:-Sometimes meteors are big in size. When these meteors enter the earth’s atmosphere, they don’t burn completely and reach the surface of earth. These unburnt pieces of meteors reaching the earth’s surface are called meteorites.

 

INTEXT QUESTIONS PAGE NO 190 

Q 1:  What are celestial bodies? Name any three.

ANS:-Bodies such as the moon, planets, sun, stars, meteors, comets etc situated in the sky are called heavenly bodies or celestial bodies.

Q 2:  Why do you classify the sun as a star?

ANS:- 1. Just as stars are bright and emit light of their own, the sun also emits  

               light and is very bright.

          2. The nuclear reaction changing hydrogen into helium taking place in the

               star is similar to the nuclear reaction taking place in the sun.

          3. Like all other stars, the sun also is stationary in its position.

              On account of above similarities the sun is classified as a star.

Q3:  Why do stars appear like point objects?

ANS:-Although stars are very big in size but because of the distance of stars from earth being very large, they appear like point objects.

Q4:  What is a constellation? How does the constellation differ from a star?

ANS:-A group of stars which forms a recognizable shape or pattern resembling some person or known object is called constellation.

           Constellation is a group of many stars and moreover it has some familiar shape of a person or object which single star does not have.

Q5:  Name a star which appears stationary from the earth. In which constellation it is situated?

ANS:-The pole star appears stationary because it is situated directly above the geographical north pole of the earth’s axis and it is situated at the tail of a constellation named “ Ursa Minor”.

 

Q6:  What is a” light minute” ? How many light minutes is the earth from the sun? Express this distance in kilometers?

ANS:-The distance travelled by light at a speed of 3,00,000 km/sec in one minute is called a light minute.

1 light minute =  3,00,000km/s *1 minute

=  3,00,000km/s * 60 sec

=  1,80,00,000 km= 18 * 10⁶km.

Distance of Earth from  the sun .

                  = 8.33Km

                   =8.33×1,80,00,000km

                   =149940000

                    =150,000000km (approx)

                    =150×10⁶km.

Q7:  How much time is involved from one new moon to another new moon as seen from the surface of the earth?

ANS:-As seen from the surface of the earth the time involved for the moon to complete one revolution between one new moon to next new moon is 29½ days.

Q8:  In how much time does the moon complete one rotation about its axis?

ANS:- The moon completes one rotation about its own axis in 27¹/₃ days.

 

INTEXT QUESTIONS PAGE NO 197

Q1: What is a planet? How many planets revolve around the sun?

ANS:-A solid heavenly body which revolves around the sun in a well defined orbit is called planet. They do not have their own light. They shine on falling of sunlight on their surface. They are made of rocks and metals. The Jupiter is the largest planet with greatest number of moons (i.e. 12) around it and mercury is the smallest planet of solar system. They are bigger than stars but do not twinkle like stars, planets change their position in the sky. All the nine  planets revolve around the sun.

 Q2: a) Name the planet which is nearest to the sun?

ANS:-Mercury.

b) Farthest from the sun?

ANS:-Neptune.

c) Supports life?

ANS:- Earth.

Q3: a) Name the planet which revolves round the sun from east to west?

ANS:-Venus.

b) Intersects the orbit of another planet?

ANS:-The orbit of Pluto intersects the orbit of planet Neptune.

Q4: Name one planet that was predicted before its discovery?

ANS:-Neptune was predicted before its discovery by French scientist U.J.J Levier.

Q5:  Name the planet having:

a) Largest number of moons.

ANS:- Saturn has the largest number of moons and the number is 30.

b) A system of number of rings.

ANS:-Saturn has system of three flat rings A,B and C.

Q6:  What is the solar system?

ANS:- The system in which nine planets, their satellites and thousands of other smaller heavenly bodies such as asteroids, comets and meteors revolve around the sun is called solar system or solar family. The nine planets that include solar system according to their increasing order of distance from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

                                        

                              

                                                   

TOPIC :- CELL       (SCIENCE)

CLASS 8^Th                                                                               

                                                                                                                                                   

Cell (The fundamental unit of life):- Cell is the structural and functional unit of life. Cells were discovered by an English scientist “Robert Hook” in 1665. Cells may exist as independent unit of life as in bacteria and certain other unicellular organisms, or they may form colonies or tissues, as in all plants and animals. Each cell consists of a mass of protein material that is differentiated into cytoplasm and a nucleus which contains DNA (Deoxyribonucleic acid) a genetic material. Cells are considered to be the building blocks of living organisms as these are the basic functional units of life. The cells of cellular organisms such as plants and animals and bacteria are divided into two types i.e. Eukaryotic and Prokaryotic cells.

 

i. Eukaryotic cells: In the cells of plants and animals the genetic material DNA is located within the nuclear membrane i.e. these cells have distinct nucleus. Such cells are called eukaryotic cells. They also have many membrane bounded organelles such as mitochondria, chloroplast, Lysosomes, endoplasmic reticulum etc. in their cytoplasm.

 

ii. Prokaryotic cells: Cells of bacteria and blue green algae do not have a distinct nucleus and the chemicals involved in cell metabolism are associated with plasma membrane. Reproduction in such cells is generally asexual and involves simple cell cleavage. Such cells are called prokaryotic cells. Their

DNA is not enclosed in nuclear membrane. They also lack organelles.

 

Cell size and Cell shape: Cells show much variation in shape and size with respect to their specific functions. Some cells change their shapes frequently such as amoeba, leucoplast (WBC) etc. while some cells like nerve cells and most plant cells have more or less fixed and typical shapes. Some of the diversified shapes of cells are polyhedral, spherical, spindle, elongated, branched, discoidal shapes etc. Most of the cells are round or oval shaped.

              The size of different cells ranges between broad limits. Some plant and animal cells are visible to the naked eye. Most of cells however, are visible only through a microscope. The size of cells varies from the very small cells of bacteria (0.2 to 0.5 μm) to the very large eggs of an ostrich (18 cm). The smallest cell is of Pleura pneumonia that of 0.1 μm and the largest cell is egg of ostrich 170 x 135 cm in size. In case of length, nerve cell is the longest cell having length of more than 1 meter.

Cell structure:- A cell is a tiny mass of cytoplasm which is limited by membrane and capable of performing all functions of life. A typical cell is formed of following parts.

i. Plasma membrane: Each cell is bounded by a thin, delicate and elastic living membrane called as plasma membrane. It is about ten thousandth of a millimeter in thickness. It is selectively permeable membrane which means it selectively allows the entry of substances into the cell and exit of substances from the cell. It provides a definite shape to the cell and provides protection to the internal contents of the cell.

 

Cell wall: In plant cells there is another protective layer outside the plasma membrane, it is called as a cell wall, which is rigid, fully permeable cellulose containing non living layer. It protects cell membrane and gives rigidity and shape to plant cell. It also prevents drying up of cells.

 

ii. Nucleus: The nucleus is a major centrally located spherical cellular component. The usual size of nucleus is 5 to 25 μm. It is bounded by two unit membranes forming nuclear membrane. Inside nuclear membrane a colourful dense sap is present, called as nucleoplasm. The nucleoplasm contains two types of nuclear structures i.e. nucleolus and chromatin. Nucleus controls all the activities of the cell.

a)    Nucleolus: It is highly dense and round organelle inside the nucleus. It is actually a mass of multiple copies of genes and acts as platform for protein synthesis.

b)   Chromatin: Inside nucleus the mass of thread like tangled structures is called as chromatin. It is composed of chromosomes which are having genetic material DNA (Deoxyribonucleic acid).

 

iii. Cytoplasm: The liquid medium of the cell around nucleus is called as cytoplasm. It is a viscous translucent, homogeneous and colloidal liquid. It contains the various organelles within it and each organelle performs a specific function for the cell.

iv. Cell organelles: The important internal parts of a cell which lies inside the cell membrane besides the nucleus are known as cell organelles. Some of the important organelles of a cell are endoplasmic reticulum(ER), Golgi apparatus, Lysosomes, Mitochondria, Plastids, and vacuoles.

 

i. Endoplasmic reticulum: The endoplasmic reticulum is a complex network of membrane bound tubules and sheets. It pervades the cytoplasm and is continuous with plasma membrane. Its main function is to serve as channels for the transport of material (proteins) between various regions of the cytoplasm or between cytoplasm and the nucleus. It also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

 

ii. Ribosomes: Ribosomes are extremely small around bodies present wither in free state in cytoplasm or attached to the surface of endoplasmic reticulum, and they are composed of RNA (Ribonucleic acid) and proteins. Ribosomes are the main sites for synthesis of proteins from amino acids.

 

iii. Golgi apparatus: These are the membrane bound fluid filled vesicles, vacuoles and stacks of many flattened cristernae (closed sacs). These are usually seen near the nucleus. Membranes of the apparatus are composed of protein and phospholipids. Various Secretions of cell are condensed, stored and processed and packed in it. Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosomes.

 

iv. Mitochondria: These are small rod shaped or spherical organelles present in large number in the cell. Their size varies between 0.2 to 2 μm x 3 to 5 μm. Each mitochondrion is bounded by two membranes, outer membrane is smooth and inner membrane is folded inwards and form cristae. Mitochondria posses oxidizing enzymes and thus release energy in the form of ATP (Adenosine Tri - phosphate), that is why mitochondria is also called as power house of the cell.

 

v. Plastids:-  Plastids occur only in plant cells and are of three types. i.e. leucoplasts and Chromoplasts & Chloroplasts.

a)    Leucoplasts: They are colourless plastids. They store the food of the plant body in the form of starch, proteins and lipids.

b)   Chromoplasts: These are organelles having various pigments or colours such as red, yellow and a variety of other colour. They are present in coloured parts of a plant such as flowers and fruits for attraction of honey bees.

c)    Chloroplasts: These are organelles having only green pigment inside and are always meant for photosynthesis of food. They are present in green leaves and green stem.

 

vi. Vacuoles: Vacuoles are fluid filled and membrane bounded spaces. In animal cells vacuoles are smaller in size and lesser in number as compared to plant cell contain many life surviving substances like amino acids, sugars, various organic acids and some proteins. Vacuoles play important role in expelling excess water and some wastes from the cell of unicellular organisms.

 

vii. Lysosomes: These are single membraned small vesicles which contain enzymes. Lysosomes are formed by Golgi apparatus. Main functions of lysosomes are digestion of food particles which are ingested by cell during endocytosis. They are defense against bacterial and viral infections and destroy the old and worn out cellular organelles. If the cell gets damaged, Lysosomes may get burst and the enzymes digest their own cell. So lysosomes are also known as suicidal bags of a cell.

 

viii. Centrosomes:- In animal cells, a minute hyaline body is present close to the nucleus. It contains two granules which are called as centrioles. Each centriole is made up of microtubules arranged in two main bundles at right angles. They help in the formation of cilia and flagella of the cells. Centrioles are yellow, cylindrical structures that are made up of microtubules but contain no limiting membranes around them.

 

Difference between plant cell and animal cell:

	Plant Cell	Animal Cell
1.	Plant cells are larger than animal cells in size.	Animal cells are smaller in size than plant cells.
2.	The plasma of membrane of plant cells are surrounded by a rigid cell wall made of cellulose.	Cell wall is absent in animal cells.
3.	Plastids are present in plant cells.	Plastids are absent in animal cell (except in protozoan euglena).
4.	Most mature plant cells have single vacuole.	Vacuoles are smaller in size and lesser in number.
5.	Plant cells have many simpler units of Golgi apparatus.	Animal cells have a single highly elaborate Golgi apparatus.
6.	Centrosomes and centrioles are not present in plant cells.	Centrosomes and centrioles are present in animal cells.
7.	Cytokines is takes place by cell plate formation.	Cytokines is takes place by constriction during cell division.
8.	Plant cells usually have angular shape.	Animal cells usually have irregular shape.

 

Difference between Prokaryotic and Eukaryotic cells:

	Prokaryotic Cells	Eukaryotic cells
1.	These are gradually small in size (1-10 μm).	These cells are larger than prokaryotic cells (50-100 μm).
2.	Nucleus is absent in these cells.	Nucleus is present in these cells.
3.	There is only one chromosome in these cells.	These cells contain more than one chromosome.
4.	The cell division in these cells takes place by fission or budding.	Cell division in these cells takes place by the process of mitosis or meiosis.

                                                  TEXTUAL QUESTIONS

Q NO 1. Define a cell?

ANS:- The basic unit of which all living things are composed is known as ‘cell’. The ‘cell’ is the smallest structural unit of living matter that is capable of functioning independently. A single cell can be a complete organism in itself, as in bacteria and protozoans. A unicellular organism also captures and digests food, respires, excretes, grows and reproduces. Similar functions in multi-cellular organisms are carried out by groups of specialized cells which are organized into tissues and organs such as, the higher plants and animals. Hence, ‘cell’ is known as the basic structural and functional unit of life.

 

Q NO 2. Who discovered the cell?

ANS:-  Cells were discovered by an English scientist “Robert Hook” in 1665.

 

Q NO 3. Give three examples of unicellular organisms?

ANS:-  Any organisms having single cell is called unicellular organism. The unicellular organisms are grouped into three categories archaea, bacteria, protozoa, unicellular algae and unicellular fungi or yeasts. This single cell perform all the functions like locomotion, reproduction, removal of waste products etc. Some examples of unicellular organisms are Bacillus, Coccus, Vibrio, Mycoplasma, Actinomytes, Amoeba, Euglena, Paramecium, Rhizopus, Saccharomyces, Chlamydomonas.

 

Q4. Answer the following questions:

(i). Why cells could not be observed before 17^th century?

Answer:- Cells, have been in existence since origin of life which took place millions of years ago. The cells could not have been seen before the 17th century because of their small size and the microscopes may not have been available or could have been very much crude. Majority of cells are too small to be seen through naked eye. Cells were seen only after the magnifying lenses and microscopes came into existence.

 

(ii). Why cork could not be observed as such by Hook?

Answer:-  Cork could not be seen as such by Robert Hook, as it is a solid structure. He found that the cork was made of box like compartments. And he named these compartments as cells.

(iii). Where did Hook demonstrate his observations on cork slice?

Answer:-  Robert Hook demonstrated his observations on cork slice to scientist at Royal Society of London.

(iv). Name the outermost layer of an animal cell?

Answer:-  Cell membrane /Plasma membrane is the outermost layer of the animal cell.

(v). Name the layer which is present outside the plasma membrane in the plant cell?

ANS:-Cell Wall is the layer present outside the plasma membrane in the plant cell.

(vi). Where are chromosomes present in a cell?

ANS:-  Chromosomes are present in the nucleus of the cell.

(vii). Name the cell part that has tiny holes?

Answer:-  Cell membrane and Nuclear membrane are the cell parts which has the tiny holes in it which allow exchange of substances between the nucleoplasm and the cytoplasm.

(viii). Name the cell organelles which are found in the plant cell?

Answer:-  Plastids are the cell organelles which are found in the plant cell.

(ix). Name the cell having branched structure?

Answer:-  Nerve cells (Neurons) are the cells having branched structures.

(x). Which cell can be observed with the unaided eye?

Answer:-  The largest cell is 170mm x 130mm, is the egg of an Ostrich which can be observed with the unaided eye.

 

Q5. Mention the functions of the following:

a)  Cell Membrane       b) Chromosomes

a)    Functions of Cell membrane:-It protects the cell, it provides shape to the cell, it allows materials to enter and leave the cell through the tiny holes.

b)   Functions of Chromosomes:-Chromosomes are thread like structures which play an important role in the inheritance of characters from one generation to another, that is from the parents to the children.

Q6.  Why are the following important to a plant cell?

i. Cell wall

Cell wall is rigid, fully permeable cellulose containing non living layer. It protects cell membrane and gives rigidity and shape to plant cell. It also prevents drying up of cells.

ii. Chloroplast

Chloroplasts contain a green pigment called chlorophyll which help in food manufacturing of plants during the process of photosynthesis.

iii. Mitochondria

Mitochondria posses oxidizing enzymes and thus release energy in the form of ATP (Adenosine Tri - phosphate), that is why mitochondria is also called as power house of the cell. They perform the functions of respiration and provide cell with energy.

iv. Nucleus

Nucleus is the master of the cell. It commands all the functioning of the cell. It is generally located in the center of the cell and is spherical in shape. A membrane called nuclear membrane separates it from cytoplasm. It contains the genetic material DNA (De-oxyribo nucleic acid) and RNA (Ribo nucleic acid) in it. This porous membrane allows the transfer of material in the nucleus and cytoplasm. Nucleus contains a dense body called Nucleolus which actually contains Chromosomes, the genetic material.

 

 

Q7. Draw an outline diagram of an animal cell. Label the different parts.

                                 

 

Q8. Mention three differences between plant cell and animal cell.

	Plant Cell	Animal Cell
1.	Plant cells are larger than animal cells in size.	Animal cells are smaller in size than plant cells.
2.	The plasma of membrane of plant cells are surrounded by a rigid cell wall made of cellulose.	Cell wall is absent in animal cells.
3.	Plastids are present in plant cells.	Plastids are absent in animal cell (except in protozoan euglena).
4.	Most mature plant cells have single vacuole.	Vacuoles are smaller in size and lesser in number.
5.	Plant cells have many simpler units of Golgi apparatus.	Animal cells have a single highly elaborate Golgi apparatus.
6.	Centrosomes and centrioles are not present in plant cells.	Centrosomes or centrioles are present in animal cells.
7.	Cytokines is takes place by cell plate formation.	Cytokines is takes place by constriction during cell division.
8.	Plant cells usually have angular shape.	Animal cells usually have irregular shape.

Q NO 9. What features are possessed by both plant cells and animal cells?

ANS:-  The features shared by both the plant as well as animal cell are

i. plasma membrane.

ii. Nucleus.

iii. Mitochondria.

iv. Endoplasmic reticulum.

v. Golgi complex.

vi. Lysosomes.

vii. Ribosomes

Q10. Why are nerve cells long? Why do these cells have projections?

Answer:-  Nerve cells have to be long enough to extend from where they are located in the body, the hands and feet for example, to the spinal cord or brain. They have fibres to send messages from the brain throughout the whole body. The nerve cells have long fibers because they have to send messages from the brain to other parts of the human body.

             Some nerve cells have fibers that grow out of the cell, which are called axons. Axons allow a nerve cell to connect to distant parts of the body, so that cells in the brain can send messages to, and receive messages from a toe, for example, which might be six feet away from the brain. Other nerve cells just connect to their immediate neighboring nerve cells, and therefore do not require axons; they instead have smaller extensions called dendrites.

 

Q11. Why are mitochondria known as the power house of the cell?

Answer:-  Mitochondria are small rod shaped or spherical organelles present in large number in the cell. Their size varies between 0.2 to 2 μm x 3 to 5 μm. Each mitochondrion is bounded by two membranes, outer membrane is smooth and inner membrane is folded inwards and form cristae. Mitochondria posses oxidizing enzymes and thus release energy in the form of ATP (Adenosine Tri - phosphate), that is why mitochondria is also called as power house of the cell.

 

Q12. Which four basic elements constitute more than 90% of protoplasm?

Answer:-  The four basic elements which constitute more than 90% of protoplasm are Carbon, Hydrogen, Oxygen, and Nitrogen.

 

Q13.  Write in brief about the variation in shape and size of cells?

Answer:-  Cells show much variation in shape and size with respect to their specific functions. Some cells change their shapes frequently such as amoeba, leucoplast (WBC) etc. while some cells like nerve cells and most plant cells have more or less fixed and typical shapes. Some of the diversified shapes of cells are polyhedral, spherical, spindle, elongated, branched, discoidal shapes etc. Most of the cells are round or oval shaped.

           The size of different cells ranges between broad limits. Some plant and animal cells are visible to the naked eye. Most of cells however, are visible only through a microscope. The size of cells varies from the very small cells of bacteria (0.2 to 0.5 μm) to the very large eggs of an ostrich (18 cm). The smallest cell is of Pleura pneumonia that of 0.1 μm and the largest cell is egg of ostrich 170 x 135 cm in size. In case of length, nerve cell is the longest cell having length of more than 1 meter.

 

Q14. Name the different cell organelles and the functions of these organelles?

ANS:-The important internal parts of a cell which lies inside the cell membrane besides the nucleus are known as cell organelles. Some of the important organelles of a cell are endoplasmic reticulum(ER), Golgi apparatus, Lysosomes, Mitochondria, Plastids, and vacuoles.

i. Endoplasmic reticulum: The endoplasmic reticulum is a complex network of membrane bound tubules and sheets. It pervades the cytoplasm and is continuous with plasma membrane. Its main function is to serve as channels for the transport of material (proteins) between various regions of the cytoplasm or between cytoplasm and the nucleus. It also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

ii. Ribosomes: Ribosomes are extremely small around bodies present wither in free state in cytoplasm or attached to the surface of endoplasmic reticulum, and they are composed of RNA (Ribonucleic acid) and proteins. Ribosomes are the main sites for synthesis of proteins from amino acids.

iii. Golgi apparatus: These are the membrane bound fluid filled vesicles, vacuoles and stacks of many flattened cristernae (closed sacs). These are usually seen near the nucleus. Membranes of the apparatus are composed of protein and phospholipids. Various Secretions of cell are condensed, stored and processed and packed in it. Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosomes.

iv. Mitochondria: These are small rod shaped or spherical organelles present in large number in the cell. Their size varies between 0.2 to 2 μm x 3 to 5 μm. Each mitochondrion is bounded by two membranes, outer membrane is smooth and inner membrane is folded inwards and form cristae. Mitochondria posses oxidizing enzymes and thus release energy in the form of ATP (Adenosine Tri - phosphate), that is why mitochondria is also called as power house of the cell.

v. Plastids: Plastids occur only in plant cells and are of two types. i.e. leucoplasts and Chromoplasts.

vi. Vacuoles: Vacuoles are fluid filled and membrane bounded spaces. In animal cells vacuoles are smaller in size and lesser in number as compared to plant cell contain many life surviving substances like amino acids, sugars, various organic acids and some proteins. Vacuoles play important role in expelling excess water and some wastes from the cell of unicellular organisms.

vii. Lysosomes: These are single membraned small vesicles which contain enzymes. Lysosomes are formed by Golgi apparatus. Main functions of lysosomes are digestion of food particles which are ingested by cell during endocytosis. They are defense against bacterial and viral infections and destroy the old and worn out cellular organelles. If the cell gets damaged, Lysosomes may get burst and the enzymes digest their own cell. So lysosomes are also known as suicidal bags of a cell.

viii. Centrosomes: In animal cells, a minute hyaline body is present close to the nucleus. It contains two granules which are called as centrioles. Each centriole is made up of microtubules arranged in two main bundles at right angles. They help in the formation of cilia and flagella of the cells. Centrioles are yellow, cylindrical structures that are made up of microtubules but contain no limiting membranes around them.

 

Q15. What is meant by protoplasm? How does it differ from cytoplasm?

Answer:-  All of the matter within the walls of the cell, including the cytoplasm, nucleus and various organelles is known as protoplasm. Protoplasm is composed of 90% water, mineral salts, gases such as oxygen and carbon dioxide, proteins, lipids, or fats, carbohydrates, nucleic acids and enzymes. Within this complex unit are numerous small bodies referred to as organelles, structures which have specific functions. The clear, jelly-like liquid which fills the cell is referred to as the cytoplasm.

 

Q NO 16. Fill in the blanks, using the words given below:

                 i.            The Lysosomes is also called as suicide bags.

               ii.            The term “Cell” was given by   Robert Hook.

             iii.            The instrument used to see tiny objects is called a microscope.

             iv.            Smallest cell is that of a Mycoplasma.

               v.            An ostrich egg is a cell that can be seen without a microscope.

             vi.            The   nucleus _, cell membrane _and _cytoplasm are parts of a cell.

           vii.            Energy is produced in mitochondria.

         viii.            Cell wall is present in plant cells.

Q17. Write “ True “ or “ False “ in front of the statement  given below.

                   Statement                                                                        True/ False

1.    Most of a cell is the nucleus.                                                       False                 

2.    Only the nucleus of a cell represents the protoplasm.             False  

3.    Most cells are microscopic.                                                          True                       

4.    All living organisms are made of cells.                                        True                     

5.    Every cell has cytoplasm.                                                            True            

6.    All cells in multi-cellular organisms can live independently.  False   

7.    The outermost covering in an animal cell is called cell wall.  False        

 

Q18. Match the statements in Column A with those in Column B

S.No.	Column A	Column B
01.	Cell	Unit of living body.
02.	Nucleus	Boss of the cells.
03.	Cell Wall	Outermost covering in plant cells.
04.	Chloroplast	Photosynthetic units.
05.	Cytoplasm	Jelly like substances between cell membrane and nucleus.
06.	Organelles	Tiny structures inside cells.

 

                               TOPIC:-SOME NATURAL PHENOMENON                             (SCIENCE)

PREPARED BY:- DAVOOD SIR. 

CLASS :-8TH                                                                           

Lightening:- Lightning is an electric spark at a huge scale. It is caused by accumulation of charges in the clouds. It is an atmospheric discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. Lightning is caused when two clouds collide or slide against one another. This involves same process which happens when we rub a comb on our dry hair and the comb gets an electric charge.                                                                   

             As amount of charge generated during collision of clouds is huge so we witness it as flashing lights in the sky. This flashing light is called lightning. Once a cloud gets electrically charged it releases the charge to earth. In other words the earth receives the charge and neutralizing the cloud in the process.

Lightening conductor: Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground. The metal columns used during construction, electrical wires and water pipes in the buildings also protect us to an extent. But do not touch them during a thunder storm.

Do’s and Don’ts during a Thunderstorm

Outside

i.        Open vehicles, like motorbikes, tractors, construction machinery, cars are not safe. So we should prefer to remain inside the vehicle and close down the doors and windows of the vehicles.

ii.      We should not remain in pen fields, under tall trees, in parks, near elevated places during lightening as these do not protect us from lightning strokes.

iii.    Carrying umbrella is not a good idea at all during thunderstorms.

iv.    If in a forest, we should take shelter under shorter trees. If no shelter is available and we are in an open field, stay far away from all trees.

v.      We should stay away from poles or other metal objects.

vi.    We should not lie on the ground. Instead, we should squat low on the ground.

Inside the house

i.        Lightning can strike telephone cords, electrical wires and metal pipes. During a thunder storm contact with these should be avoided.

ii.      It is safer to use mobile phones and cordless phones.

iii.    Bathing should be avoided during thunderstorms to avoid contact with running water.

iv.    Electrical appliances like computers, TVs, etc., should be unplugged. Electrical lights can remain on. They do not cause any harm.

Construction and working of an electroscope: An electroscope can be used to detect whether a body is charged or not. It consists of a metal rod. At one end of the rod, two leaves of aluminium foil are fixed and at the other end, there is a metal disc. The leaves of aluminium foil are placed inside a conical flask and the flask is corked to isolate the leaves from air.                                                                                                   

             When the metal disc is touched with a charged body, the aluminium strips move away from each other. This happens because some of the charges of the body are transferred to the strips through the metal rod. This method of charging a body is called charging by conduction. The nature of charges on both the leaves and the charged body are the similar. Hence, both the leaves of the aluminium foil will move away from each other. If the body was not charged, then the leaves of the foil would remain as they were before. They would not repel each other.

                                            

 

Earthquakes: An earthquake is a sudden shaking or trembling of the earth lasting for a very short time. It is caused by a disturbance deep inside the earth’s crust. Earthquakes occur all the time, all over the earth. They are not even noticed. Major earthquakes are much less frequent. They can cause immense damage to buildings, bridges, dams and people. There can be a great loss to life and property. The earthquakes can cause floods, landslides and tsunamis.

Causes of Earthquake: The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a tectonic plate. These plates are in continual motion. When they brush past one another, or a plate goes under another due to collision, they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.                                                                               

               Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out. However, most earthquakes are caused by the movement of earth’s plates. Since earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones. The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale. Really destructive earthquakes have magnitudes higher than 7 on the Richter scale. In India, the area’s most threatened are Kashmir, Western and Central Himalayas, the whole of North East, Rann of Kutch, Rajasthan and the Indo – Gangetic Plane. Some areas of South India also fall in the danger zone

Protection against Earthquakes: The various protection steps to be taken against the earthquakes are

i.        We should consult qualified architects and structural engineers to get our houses designed and built in such a way that in case the structure falls during an earthquake, the damage will not be heavy.

ii.      In highly seismic areas, the use of mud or timber is better than the heavy construction material. Roofs should be as light as possible.

iii.    It is better if the cupboards and shelves are fixed to the walls, so that they do not fall easily during an earthquake.

iv.    We should be careful when we hang wall clocks, photo-frames, water heaters etc., so that in the event of an earthquake, they do not fall on people.

v.      Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have firefighting equipment in working order.

                                            

                                           TEXTUAL QUESTIONS

Select the correct option in Questions 1 and 2

Q NO 1:-Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth
    ► ANS:- (b) A copper rod

Q NO 2:-When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
► ANS:-(b) becomes positively charged while the cloth has a negative charge.

Q NO 3:-Write T against true and F against false in the following statements.

(a) Like charges attract each other. (T / F)
► False

(b) A charged glass rod attracts a charged plastic straw. (T / F)
► True

(c) Lightning conductor cannot protect a building from lightning. (T/F)
► False

(d) Earthquakes can be predicted in advance. (T / F)
► False

Q NO 4:-Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

 ANS:-Sweater is made of wool and generally shirt we wear is made of cotton blended with some synthetic fibers. Constant friction between the shirt and sweeter lets transfer of electrons from one material to the other. This results in building of electric potential. When enough potential has been accumulated, while taking of the sweater it discharges and transfer of electrons take place. Passage of electrons through air in the forms of spark let out heat and sound energy. Thus we hear the crackling sound and in dark rooms we may see the spark lights as well.

Q NO 5:-Explain why a charged body loses its charge if we touch it with our hand.
ANS:-When we touch a charged body, with our hand, the excess of accumulated charge or static charges on it, gets transfer to ground through our body. Thus the charged body loses its charge, and becomes neutral.

Q NO 6:-Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

ANS:-The destructive energy of an earthquake is measured on Richter Scale.

The reading of magnitude 3 on the Richter scale would be recorded by a seismograph.
       If the Richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage. Generally, earthquake of magnitudes higher than 5 is considered destructive in nature.
Q NO 7:-Suggest three measures to protect ourselves from lightning.

ANS:-Protective measures against lightning are:-

→Stay indoor or under covered area.
→ Do not take bath during lightning.
→ Do not use any electrical appliances during lightning.

Q NO 8:-Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

ANS:-A charged balloon is repelled by another charged balloon because both carry same charges and we know same charges repel each other whereas an uncharged balloon is attracted by charged balloon because unlike charges attract each other.

QNO 9:-Describe with the help of a diagram an instrument which can be used to detect a charged body.

ANS:-An electroscope can be used to detect whether a body is charged or not. The following figure shows a simple electroscope.

                                            

In an Electroscope, two metal foils are are hanged with the help of a conductor in a glass jar with a lid. When a charged body touches this conductor, its charged gets transferred to the metal foil and they move apart due to like charges. This shows that an electroscope detects charges.

Q NO 10:-List three states in India where earthquakes are more likely to strike.
ANS:-The three states in India where earthquakes are more likely to strike are Jammu and Kashmir, Gujrat, and Assam.

Q NO 11:-Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

ANS:-Some of the precautions are:

→ Try to move to an open space.
→ We should not take shelter under trees, buildings or overhead power lines.
→ If travelling in a bus or a car, then do not come out when an earthquake strikes. Ask the driver to drive in an open field.