Class X Solution of OUR ENVIRONMENT

I.Very short answer type questions: 

1. Mention one negative effect of our affluent lifestyle on the environment.
   Ans. Global warming is a negative effect in which the amounts of greenhouse gases like CO₂ have been increasing due to the uses of a large number of vehicles and industries.
2. What are the advantages of cloth bags over plastic bags during shopping?
   Ans. Plastic bags are non-biodegradable whereas cloth bags are biodegradable and they do not pollute the environment.
3. Why is improper disposal of waste a curse to the environment?
   Ans. Improper disposal of waste a curse to the environment because it can cause contamination of groundwater, surface, pollution of the environment and harmful effect of human health. 
4. Write the common food chain of a pond ecosystem.
   Ans. The common food chain of a pond ecosystem is 
   Algae →small animals → insects → small fish → big fish → fish-eating birds.
5. Which chemical is used in a fire extinguisher? How it is harmful?
   Ans. Chlorofluorocarbon (CFCs) are used in a fire extinguisher. The amount of ozone in the atmosphere decreases due to this synthetic harmful chemical. 
6. Why are crop fields known as an artificial ecosystem?
   Ans. Crop fields are man-made ecosystem so they are called artificial ecosystems.
7. State a way to prevent the accumulation of harmful chemicals in our bodies.
   Ans. We can prevent the accumulation of harmful chemicals in our bodies by drinking more and more water, by eating vegetables and by taking detox food.
8. List two non-biodegradable waste generated daily in the kitchen which can be recycled.
   Ans.  Milk packets and empty medicine bottles are the two non-biodegradable waste generated daily in the kitchen which can be recycled. 
9. Consider a food chain consists of Wheat, Rat, Snakes, and Peacock. What will happen if all the snakes are killed?
   Ans. If all snakes are killed then the population of the rat will increase and maximum wheat will be finished by rat and when the snakes are killed the number of peacock decreases because of hunger.
10. Choose one consumer each that belongs to the second and third trophic levels from the organisms. Eagle, Frog, Tiger, Rabbit, Fox.
    Ans. Frog and rabbit belong to 2nd and Fox, tiger and eagle belong to 3rd level.
11. Pesticides added to a field are seen in an increased amount in the crop and in the bird that feeds on them. What is this phenomenon called?
    Ans. The phenomenon is known as biological magnification.
12. What happens during the first step of ozone formation in the atmosphere?
    Ans. The higher energy UV radiations split some molecular oxygen (O₂) into free oxygen (O) atoms and these atoms then combine with the molecular O₂ oxygen to form ozone O₃. 
    O₂ + UV→O + O  
    O + O₂ → O₃ Ozon.
13. List two main components of our environment. Why are green plants called producers?
    Ans. Biotic and abiotic are the two main components of our environment. All green plants can produce food by photosynthesis so they are called the producers.
14. Define ecosystem. 
    Ans.  An ecosystem is a system that consists of biotic components (living organisms) and abiotic components (physical factors- temperature, rainfall, wind, soil, and minerals).
15. Name the chemical compound which depletes the Ozone Layer.
    Ans. The synthetic chemical Chlorofluorocarbons (CFCs) are used as refrigerants and in fire extinguishers that deplete the Ozone Layer.
16. Name the organisms belonging to 4th trophic levels in the food chain comprising of snakes, insects, frogs, plants, and hawks.
    Ans. From the food chain
    Plant → Insects → Frogs → Snakes → Hawks.
    The organism at the fourth trophic level is snakes.
17. Name the two abiotic components of the ecosystem.
    Ans. Temperature and rainfall are the two abiotic components.
18. Mention the role of microorganisms like bacteria and fungi.
    Ans. The microorganisms like bacteria and fungi are the decomposers, break-down the complex organic substance such as dead remains and waste products of organisms into simple inorganic substances.
19. In the following food, chain grass provides 4000 J of energy to the grasshopper. How much energy will be available to Snakes and frog?
    Ans. If grass provides 4000J energy to the grasshopper then it will give 10% of its energy to the next trophic level.
    Therefore 10% of 4000J = 400J energy will be available to frog and 10% of 400J = 40J will be available to the snake.
20. State any two possible consequences of the elimination of decomposers from the earth.

    Ans. If decomposers are eliminated from the earth, dead remains and organic waste will be accumulated in the environment and this would-be polluting the soil, ecosystem and water bodies.
21. Write any four examples of abiotic factors.
    Ans. Biotic factors are physical factors:
    Example of four abiotic factors- temperature, wind, rainfall, soil.
22. If autotrophs occupy the first trophic level are called producers then what are herbivores called?
    Ans. If autotrophs occupy the first trophic level are called producers then the herbivores are the primary consumers come at the second trophic level as they eat producers.
23. What are biotic factors ? Give any two examples.
    Ans. Biotic factors are the living components comprising living organisms. Two examples -animals and plants.
24. What is the full form of UNEP and CFCs?
    Ans. The full form of UNEP is the United Nations Environment Programme and the full form of CFCs is Chlorofluorocarbons.

II. Short answer type questions : 

1. In some states of our country, there is a ban on the use of Polythene bags for shopping. Why? List three advantages of using jute or cloth bags over Polythene bags.
   Ans. Plastics are non-biodegradable and may be inert and simply persist in the environment for a long time and may harm the various members of the eco-system. So some states of our country are the ban on the use of polythene bags for shopping.
   Three advantages of using jute are:
   (i) Jute is biodegradable, (ii) It is cheaper than plastic, (iii) It is long-lasting and durable.
2. Differentiate between food chain and food web.
   Ans.  The main difference between food chain and web are as follows:-
   (a) Food chains show only one chain of connected plants and animals with their food habits while the food web shows the various different plants and animals in an ecosystem.
   (b) A food chain is a single path of plants and animals while a food web is a collection of many food chains.
   (c) A food chain is unstable in an ecosystem while a food web is stable in an ecosystem.
3. Differentiate between household wastes and industrial waste.
   Ans. Different between household wastes and industrial waste:
   (a) Household wastes are may be biodegradable and can be recycled while industrial waste is non-biodegradable, synthetic and harmful for the environment.
   (b) Household wastes can be decomposed by decomposers while industrial wastes cant be decomposed by decomposers.
4. In a food chain comprising Tiger, Plants, and Goat, which will transfer the maximum amount of energy and receive a minimum amount of energy.
   Ans. In a food chain" Plants → Goat→ Tiger", plants will transfer the maximum amount of energy as they are in the first level and tigers receive a minimum amount of energy as they present in the last level. 
5. What is the by-product of fertilizer industries? How do they affect the environment?
   Ans. The by-products of the fertilizer industries are different chemicals like SO2, CO, CO2, H2S, nitrous oxide, methane gas, Calcium Carbonate, plastic bag. 
   Effect on Environment: The gaseous by-products like carbon dioxide,  methane are greenhouse gases that cause global warming and the gases like sulfur dioxide and nitrous oxide are air pollutants and lead to acid rain. 
6. Why is the Government of India imposing a ban on the use of Polythene bags? Suggests an alternative to these bags and explain how this man is likely to improve the environment.
   Ans. Plastics are non-biodegradable. Plastics may be inert and simply persist in the environment for a long time and may harm the various members of the eco-system. The Government of India imposing a ban on the use of Polythene bags.
   An alternative to these bags is a cloth bag or jute bag. Cloth bags or jute bags are biodegradable. They are ecofriendly, cheaper than plastic, long-lasting and durable.
7. Explain some harmful effects of agricultural practices on the environment.
   Ans. During agricultural practice, to protect our crops from diseases and pests we use several pesticides. These pesticides are either washed down into the soil or into the water bodies which are absorbed by the plants along with water and minerals and from the water bodies, these are taken up by aquatic plants and animals. The concentration of these chemicals or pesticides gets accumulated in plants, animals and the human body.
8. List two environment-friendly practice or habits which need to be followed by every member of the family community. Explain how this practice will support a safe environment mission.
   Ans. Two environment-friendly practice are:
   (i) Every member of the family community should use of jute bags/ cloth bags/ paper bags instead of plastic bags - Jute bags/clothes bags/ paper bags are biodegradable substances as they are easily decomposed by decomposers or recycled.  
   (ii) Use separate bin to dispose of biodegradable and non-biodegradable waste - By this method, biodegradable wastes can be easily disposed of by for compositing while non-biodegradable wastes can be sent for recycling. These help in protecting the environment from pollution. 
9. What are the top carnivores? Give two examples.
   Ans. The fourth trophic level animals are known as top carnivores or the territory consumers. The fourth trophic level is formed by the tertiary consumers. Two examples are tigers and hawk.
10. Write any four effects of ozone depletion on our health.
    Ans. Four effects of ozone depletion on our earth are:
     (i)  It causes skin cancer in human beings.
    (ii) It increases global warming,
    (iii) Harmful effects are observed due to exposure to UV radiation.
    (iv) Ozone depletion causes UV radiation to enter the earth's atmosphere. 
11. In the food chain, grass → deer → lion operating in a forest, what will happen if (i) all the lions and (ii) deers are removed?
    Ans. In the food chain of grass → deer → lion operating in a forest:
    (i) If all lions are removed then the deer's population will increase which leads to overeating of grass and no grass will be left and deer will automatically die leads to the destruction of the complete food chain.
    (ii) If all the deers are removed then food available for lions would be less and they all get to die.
12. Why are only four or five trophic levels present in each food chain?
    And. Only four or five trophic levels present in each food chain because of an average of 10% of the food eaten is turned into its own body and made available for the next level of consumers and each organism on that level loses energy gained from the previous trophic.
13. Industrialization is one of the main causes of depletion of the environment. List any four reasons in favour of this statement.
    Ans. The four reasons for the main cause of depletion of the environment are :
    (i) Harmful chemicals released from the industry are going to the water bodies.
    (ii) Polluted water and waste released by industry pollute the water bodies. Harmful gases release by it pollute the atmosphere.
    (iii) Sound pollution happens due to its. 
    (iv ) Dumping of nonbiodegradable waste pollutes the environment.
14. Why do enzymes which breakdown carbohydrates in food do not break down coal?
    Ans. Enzymes that breakdown carbohydrates in food do not break down coal because enzyme does not break-down everything, they are specific in their action, specific enzymes can break-down a particular substance and do not breakdown coal. Coal is a nonbiodegradable substance. 
15. Discuss the feeding pattern in a food web.
    Ans.  Instead of a straight line food chain, the relationship can be seen as a series of branching, lines called a food web. Each organism obtains food from more than one type of organism of the lower trophic level and after that, they are generally eaten by two or more other kinds of organisms.
16. What is ozone? How does it protect the organisms on earth?
    Ans. Ozone O₃ is three atoms of oxygen O₂ molecules. Ozone is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It protects the surface of the earth from ultraviolet (UV) radiation from the Sun. UV radiation is highly damaging to organisms, It can cause skin cancer, darken the skin, etc in human beings. 
17. Observe the food chain. A plant (1000 kj), Goat, Lion. How much energy does the Lion get in the above food chain?
    Ans. As we know that an average of 10% of the food eaten is turned into its own body and made available for the next level of consumers, so in the food chain of Plants → Goats → Lions, the goat will gain 10% of 1000Kj = 100Kj and after that lion will get 10% of 100 = 10kj.
18. What is the ecosystem? List two main components.
    Ans.  An ecosystem is a system that includes living things in a given area and the nonliving environment. It consists of two components biotic components (living organisms) and abiotic components (physical factors- temperature, rainfall, wind, soil, and minerals).
19. Plankton ➝Small fish ➝ Large fish ➝ man. DDt has entered the food chain and caused serious damage to human health. Provide a solution to this problem.
    Ans. Planktons absorb the DDt. When the planktons are eaten by small fishes, the DDt enters the fishes. Larger fish eat small fishes that create a high concentration of DDt in the large fish. People eating those contaminated large fish may get DDt poisoning which may cause serious damage to human health.
    So, I think that the use of DDt should be banned.
20. Give any two examples of each:
    (a) Organisms occupying the first trophic level.
    (b) Carnivores.
    (c) Biodegradable waste of humans.
    (d) Ecosystems.
    (e) Abiotic factors of an ecosystem.Ans. Two examples of each:
    (a) Organisms occupying the first trophic level - Green plants and algae,
    (b) Carnivores - Tiger and lion,
    (c) Biodegradable waste of humans - Human or animal excreta and kitchen waste.
    (d) Abiotic factors of an ecosystem - Temperature and soil and minerals.
21. It is said there is a need to put a blanket ban on the products containing aerosols. What are aerosols? Why is there a demand to put a ban on them?
    Ans. An aerosol is a colloidal system of solid or liquid particles in a gas. An aerosol includes both the particles and the suspending gas, which is usually air.Aerosols need to be banned because chlorofluorocarbons (CFCs)  are used in them as propelling agents that keep the pressure in the can constant.
22. Consider a food chain of the following fish, crab, and plankton shark. Arrange the above chain in the proper order of the trophic level. Mention the role of decomposers in our ecosystem.
    Ans. The food chain is: Plankton → Crab → Fish → Shark.
    Decomposers such as fungi and bacteria help in the recycling of nutrients. They feed on the dead and decaying bodies of plants and animals and return the nutrients back to the soil and thus help in making this ecosystem stable.
23. Mention any three significances of a food chain.
    Ans. (a) Food chains show only one chain of connected plants and animals with their food habits and it is unidirectional.
    (b) The food chain helps in studying feeding relationships between organisms and energy is transferred from one trophic to another.
    (c) A food chain is unstable in an ecosystem.

III.Long answer type questions: 

1. What is meant by the food chain? The number of trophic levels in a food chain is limited. Give reasons to justify this statement.
   Ans.  It is a series of organisms feeding on one another. This series or organisms taking part in various biotic levels form a food chain. 
   In an ecosystem, producers capture about 1% of the energy of sunlight to convert it into food energy and when they are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. There is a progressive decline in the amount of energy at each trophic level and due to this, the number of trophic levels in a food chain is limited.
2. We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.
   Ans. The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the aquatic plants. But the aquarium does not contain soil and decomposers such as bacteria and fungi which are act as a cleaner, so we need to be cleaned regularly.
3. Our food grain such as wheat and rice, the vegetables and fruits and even meet are found to contain varying amounts of pesticide residue. State the reasons to explain how and why it happens?
   Ans. We use many pesticides and chemicals to protect our crops from diseases and pests. These chemicals are washed down into the soil and into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies, these are taken up by aquatic plants and animals. This way pesticides enter the food chain and are found to contain varying amounts of pesticide residue in our food grain such as wheat and rice, the vegetables and fruits and even meet.
4. What are decomposers? List two important roles they play in the environment. List two reasons to show that the existence of decomposers is essential in an ecosystem.
   Ans.  The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms, these microorganisms are called decomposers. 
    Decomposers break-down the complex organic substances such as garbage, and dead animals and plants into simple inorganic substances that go into the soil and are used up once more by the plants and the natural replenishment of the soil take place.
   Therefore two reasons to show that the existence of decomposers is essential in an ecosystem are:
   1) They help in the recycling of nutrients by decomposing dead plants and animals and
   2) They help in keeping the environment clean. 
5. The maximum concentration of harmful chemicals accumulates in human beings. State the phenomenon involved and justify this statement.
   Ans. The uses of many pesticides and chemicals to protect our crops from diseases and pests are washed down into the soil and into the water bodies from where pesticides and chemicals are absorbed by the plants and aquatic animals along with water and minerals. In these ways, these chemicals enter the food chain and these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in human bodies. This phenomenon is known as biological magnification. 
6. Give any two ways in which biodegradable substances would affect the environment.
   Ans. Two ways in which biodegradable substances would affect the environment are:
   (i) Biodegradable substances like kitchen wastes, tree leaves, clothe bags, clothes, paper bags, plant parts, etc can be used as humus after composting which will enhance soil fertility.
   (ii) Biodegradable substances produce foul smell during the decomposition process and they produce some harmful gases such as methane, ammonia, carbon dioxide, etc which can cause global warming.
7. Give reasons: 
   (a) kulhads have been a band for serving tea or platform.
   (b) Decomposers are not included in any food chain.
   Ans. (a) Kulhads are made up of clay. kulhads have been a band for serving tea or platform because making these kulhads on a large scale would result in the loss of the fertile top-soil. 
   (b)The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers. As they decompose every organism at each trophic level of the food chain, so the decomposers are not included in any food chain. 
8. Why produces are transducers' energy?
   Ans. The function of the transducer is to convert one form of energy into another form of energy. Producers are transducers because they synthesized by the process of photosynthesis in which solar energy converted into chemical energy with the help of water and carbon dioxide and serves as an energy source for the next trophic level. From autotrophs, the energy goes to the heterotrophs and decomposers and this energy is and this energy is transferred to the next trophic level (primary consumers). 
9. What are the problems caused by the non-biodegradable wastes that we generate?
   Ans. The problems caused by the non-biodegradable wastes that we generate:
   (i) Non-biodegradable wastes may be inert and simply persist in the environment for a long time and may harm the eco-system. 
   (ii) Dumping of nonbiodegradable waste pollutes the environment.
   (iii) The non-biodegradable substance is synthetic like plastic, the glass may harm animals, aquatic animals and block drains,
   (iv) Nonbiodegradable like synthetic chemicals may enter the food chain and can harm humans and animals.
   (v) Nonbiodegradable like a radioactive substance causes diseases in living organisms.
10. What are consumers? Name the four categories into which the consumers are farther grouped.
    Ans. The organisms which cannot synthesize their own food from inorganic sources and depend on the producers for their food either directly or indirectly for their sustenance are known as consumers.  
    Consumers can be categories as herbivores, carnivores, omnivores, and parasites.
    Herbivores are primary consumers who come at the second trophic level of the food chain. They eat green plants and vegetables. Example- deer, goat, rabbit, etc.
    Carnivores are secondary consumers and come at the third trophic level. They depend on primary consumers like a goat, deer. Example- lion, tiger, etc.
    Omnivores are the ones who eat both plants and meat. Example- bears, humans, crows, etc.
11. Explain the phenomenon of Biological magnification. How does it affect organisms belonging to different trophic level particularly the territory consumer?
    Ans. The uses of many pesticides and chemicals to protect our crops from diseases and pests are washed down into the soil and into the water bodies from where pesticides and chemicals are absorbed by the plants and aquatic animals along with water and minerals. In these ways, these chemicals enter the food chain and these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in human bodies. This phenomenon is known as biological magnification.
    Our food grains such as wheat and rice, vegetables and fruits, meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means and enter our bodies through these.
12. Damage to the Ozone layer is a cause for concern. Justify this statement. Suggest any two steps to limit this damage.Ans. Ozone is a poison substance. However, ozone performs an important function. It protects the earth's surface from ultraviolet (UV) radiation of the Sun. This radiation can damage the organisms. It may cause skin cancer, darken the skin in human beings.
    The amount of ozone in the atmosphere began to drop sharply due to the use of synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. 
    Two steps to limit this damage are: (i) Reduce the use of ozone-depleting substances chlorofluorocarbons (CFCs).
    (ii) Do not use CFCs or ban on the production of the chlorofluorocarbons (CFCs).
13. Why is only 10% of energy made available to the next trophic level when green plants are eaten by herbivores?
    Ans. In an ecosystem, producers such as green plants capture about 1% of the energy of sunlight to convert it into food energy and when they are eaten by primary consumers such as goat, deer which are herbivores, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. In this way, there is a progressive decline in the amount of energy at each trophic level.
14. What is ozone? Show the reactions of the formation of ozone from oxygen in the atmosphere.
    Ans. Ozone O₃ is three atoms of oxygen O₂ molecules. Ozone is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It protects the surface of the earth from ultraviolet (UV) radiation from the Sun. UV radiation is highly damaging to organisms, It can cause skin cancer, darken the skin, etc in human beings. The higher energy UV radiations split some molecular oxygen (O₂) into free oxygen (O) atoms and these atoms then combine with the molecular O₂ oxygen to form ozone O₃. 
    O₂ + UV→O + O  
    O + O₂ → O₃ Ozon.
15. When did the amount of ozone in the atmosphere beings to draw sharply? Why did this happen? How was this problem taken care of by UNEP?
    Ans. The amount of ozone in the atmosphere began to drop sharply in the 1980s.
    This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. 
    In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.
16. What are tropic levels? Give an example of a food chain and state the different trophic levels in it.
    Ans. Each level of the food chain of living organisms forms a trophic level. There are four levels. First (producers), second (primary consumers), third (secondary consumers) and fourth trophic level (Humans, tiger, lion, etc).
    Example- Plant → Insects → Frogs → Snakes → Hawks.
    Plants are producers and are come at the first trophic level. The primary consumers' insects come at the second, small carnivores or the secondary consumers' snake at the third and larger carnivores or the tertiary consumers' hawks come at the fourth trophic level. 
17. I. Calculate the amount of energy is available to Lion in the following food chain if plants have 2000 joules of energy available from the sun.   Plant ➝Deer➝Lion.
    II. Why there is a progressive decline in the amount of energy at each trophic level?
    Ans. I. As we know that an average of 10% of the food eaten is turned into its own body and made available for the next level of consumers, so in the food chain of Plants → Deer → Lions, the deer will gain 10% of 2000Kj = 200Kj and after that lion will get 10% of 200 = 20kj.
    II. In ecosystem producers capture about 1% of the energy of sunlight to convert it into food energy and when they are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. In this way, there is a progressive decline in the amount of energy at each trophic level.
18. On what basis are organisms grouped as producers consumers and decomposers. Write two problems that would arise if there were no decomposers in an ecosystem. 
    Ans. The organisms which cannot synthesize their own food from inorganic sources and depend on the producers for their food either directly or indirectly for their sustenance are known as consumers.  
    The organisms at the first trophic level are the autotrophs or the producers. They convert solar energy into chemical energy and make it available for the second level such as heterotrophs or the consumers. 
    Organisms breaking down the waste of living beings, dead plants and animals are called decomposers.
    If there were no decomposers in the environment it would lead to the accumulation of dead plants and animals in the environment which causes harmful diseases.
19. Define the following:
    (a) Food chain (b) Trophic level
    (c) Producers (d) Parasites 
    (e) Non-biodegradable substances.
    Ans. (a) Food chain -  It is a series of organisms feeding on one another. This series or organisms taking part in various biotic levels form a food chain. 
    (b) Trophic level-Each level of the food chain forms a trophic level. There are four levels. First (producers), second (primary consumers), third (secondary consumers) and fourth trophic level (Humans, tiger, lion, etc) 
    (c) Producers - The organisms at the first trophic level are the autotrophs or the producers. They convert solar energy into chemical energy and make it available for the second level such as heterotrophs or the consumers. 
    (d) Parasites- Parasites are the organisms which must live on or in another organism such as plants and human to survive. 
    Example-  hookworm, threadworm, protozoa, hair and body lice, 
    (e) Non-biodegradable substances- Substances that are not broken down in simpler substances are said to be non-biodegradable. Example- plastic, glass, etc.
20. Name the following:
    (a) Organisms feeding on animal and plant food.
    (b) Organisms breaking down the waste of living beings.
    (c) The organisms occupying the first trophic level of any food chain.
    (d) A complex network of much-interconnected food chains and feeding relationships.
    (c) The cumulative increases in the concentrations of the persistent substances in successively higher levels of the food chain.
    Ans. (a) Organisms feeding on animal and plant food - Omnivores such as bear, human, etc.
    (b) Organisms breaking down the waste of living beings - Decomposers
    (c) The organisms occupying the first trophic level of any food chain- Producers such as green plants.
    (d) A complex network of much-interconnected food chains and feeding relationships- Food web.
    (c) The cumulative increases in the concentrations of the persistent substances in successively higher levels of the food chain - Biomagnification.
21. We often observe domestic waste decomposing in the by-lanes of residential colonies. Suggest ways to make people realize that improper disposal of waste is harmful to the environment.
    Ans. Improper disposal of waste is harmful to the environment in the following ways: 
    (i) Improper disposal of waste will release harmful gases in the environment which is harmful to the environment.
    (ii) Improper waste may be flow to the water body by the rainwater which causes water pollution and it could be harmful to the aquatic animals.
    (iii) The improper disposal of waste creates a place for the breeding place for mosquitoes and that housefly which carries many diseases.
22. Energy flow in a food chain is directional. Justify this statement.
    Ans. Each level of the food chain forms a trophic level. It is a single path of plants and animals so that they eat each other. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for the second level primary consumers, the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level. This way we can say that energy flow in a food chain is directional.
23. Explain how the pesticides enter a food chain and subsequently get into our body.
    Ans. The uses of many pesticides and chemicals to protect our crops from diseases and pests are washed down into the soil and into the water bodies from where pesticides and chemicals are absorbed by the plants and aquatic animals along with water and minerals. In these ways, these chemicals enter the food chain and these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in human bodies.