CBSE Class 10 Science Our Environment Sure Shot Questions Set 03

These are 22 sure shot board-style questions with answers for CBSE Class 10 Science Chapter 13, Our Environment, chosen from the questions that appear most often in school and board examinations. They cover the ecosystem and its energy flow, food chains and the food web, biological magnification, the ozone layer and the CFC agreement, and the methods of waste disposal, each answered step by step.

Ecosystem, Food Chain and Energy Flow

Question 1. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.
Answer:
An ecosystem is the interaction of all the biotic (living) and abiotic (non-living) components present in a particular area. Ponds, forests and grasslands are examples.
Energy flows across the trophic levels following the 10% law: only 10% of the energy available at a trophic level is passed on to the next level. The rest is lost as heat.

In simple words: An ecosystem is living and non-living things working together, and energy flows through it in one direction.

Teacher's Note:
1. Draw the boxes in the order Sun, producers, herbivores, carnivores.
2. Show the heat loss at each step.

Question 2. What are trophic levels? Give an example of food chain and state the different trophic levels in it?
Answer:
The distinct sequential steps or levels in a food chain where the transfer of energy takes place are called trophic levels.
Example: Grass → Grasshopper → Lizard → Snake → Hawk.
Grass (producer) is the first trophic level, grasshopper (primary consumer) the second, lizard (secondary consumer) the third, snake (tertiary consumer) the fourth and hawk (quaternary consumer) the fifth.
In simple words: Each step of a food chain is a trophic level.

Teacher's Note:
1. Name the type of consumer at each level.
2. Most food chains have only three or four steps.

Question 3. What are decomposers? What will be the consequence of their absence in an ecosystem?
Answer:
Decomposers are micro-organisms such as bacteria and fungi that feed on dead plants and animals and break down their complex organic substances into simple inorganic substances.
In their absence dead plants and animals and wastes would pile up, and the nutrients would not return to the soil for the producers to use again, so recycling of matter would stop and the ecosystem would collapse.
In simple words: Decomposers clean up and recycle; without them wastes pile up.

Teacher's Note:
1. Mention bacteria and fungi.
2. Describe both the cleaning and the recycling role.

Question 4. Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies? What is this phenomenon called?
Answer:
A food chain is the sequence of living organisms in a community in which one organism consumes another to transfer food energy.
A terrestrial food chain of four trophic levels: Grass → Insect → Frog → Bird.
The pollutant is not broken down and increases at each level, so the organism at the highest trophic level, the bird, has the maximum concentration. The phenomenon is called biological magnification.
In simple words: Non-degradable pollutants pile up most in the top consumer.

Teacher's Note:
1. Name the top organism of your own food chain.
2. Write biological magnification at the end.

Question 5. (i) ‘Energy flow in a food chain is unidirectional’. Justify this statement. (ii) Explain how the pesticides enter a food chain and subsequently get into our body.
Answer:
(i) Producers convert solar energy into chemical energy, and the herbivores and carnivores get it by eating. The energy captured by the producers does not return to the Sun, and the energy passed to herbivores does not come back to the producers. Only 10% passes to the next level and the rest is lost as heat, so energy moves in one direction only.
(ii) Pesticides sprayed on crops are washed into the soil and water bodies. They are absorbed by plants along with water and minerals, and by aquatic plants and animals. Being non-biodegradable they are not broken down and accumulate at every trophic level. Human beings are at the top, so these chemicals collect in our bodies in a large amount.
In simple words: Energy goes one way; pesticides build up as they move up the food chain.

Teacher's Note:
1. Use the words non-biodegradable and biomagnification in part (ii).
2. This is a very frequent board question.

Question 6. Why is damage to the ozone layer a cause of concern? What steps are being taken to limit this damage?
Answer:
The ozone layer in the stratosphere prevents the harmful UV rays of the Sun from entering the Earth’s surface. Ozone depleting substances such as CFCs damage it, so more UV reaches the Earth and causes genetic disorders, mutations, skin cancer and eye diseases in humans, and also affects plants and animals.
In 1987 the United Nations Environment Programme (UNEP) got the nations to agree to freeze the production of CFCs at the 1986 level, and CFC-free refrigerators were made compulsory. CFCs are being replaced by safer alternatives.
In simple words: Less ozone means more UV, which harms life; CFC production is therefore controlled.

Teacher's Note:
1. Note the year 1987 and the name UNEP.
2. The agreement is called the Montreal Protocol (signed in 1987).

Question 7. Briefly describe different methods of wastes disposal?
Answer:
(1) Landfills: wastes are dumped in low lying areas and covered with soil.
(2) Recycling: paper, plastics and metals are sent to recycling plants to make new products.
(3) Composting: kitchen waste and vegetable peels are converted into manure.
(4) Incineration: medical and chemical wastes are burnt at a high temperature and the ash is put in landfills.
(5) Biogas production: biodegradable wastes are used in biogas plants to produce fuel.
In simple words: Dump, recycle, compost, burn or make biogas, depending on the waste.

Teacher's Note:
1. Match every method to a type of waste.
2. Name at least four methods.

Question 8. (a) What is an ecosystem? List its two main components. (b) We do not clean ponds or lakes, but an aquarium needs to be clean regularly, explain.
Answer:
(a) An ecosystem is made up of different organisms and their physical surroundings, interacting with each other. Its two main components are biotic (living) and abiotic (non-living) components.
(b) A pond or lake is a natural, self-sustaining and complete ecosystem with producers, consumers and decomposers, which keep the water clean. An aquarium is an artificial and incomplete ecosystem without natural decomposers, so the fish waste and left-over food collect and must be removed by cleaning.
In simple words: Natural ecosystems clean themselves; an aquarium does not.

Teacher's Note:
1. Use the words natural and artificial in your answer.
2. Decomposers are the key idea.

Teacher's Note:
1. Present the answer as a table.
2. Mention stability.

Question 10. “The maximum concentration of harmful chemicals accumulates in human beings.” State the phenomenon involved and justify this statement.
Answer:
The phenomenon is biomagnification (biological magnification).
Harmful chemicals such as pesticides are non-biodegradable, so their concentration increases at every trophic level. Human beings are placed at the top of every food chain, so the maximum concentration accumulates in their bodies.
In simple words: Humans are at the top of the food chain, so they collect the most chemicals.

Teacher's Note:
1. Name the phenomenon first.
2. Give the reason: non-biodegradable and top position.

Question 11. What are the problems caused by the non-biodegradable wastes that we generate?
Answer:
(1) They cannot be degraded naturally, so they accumulate in the soil, causing pollution and reducing soil fertility.
(2) Some, such as DDT and mercury, enter the food chain and undergo biological magnification.
(3) Burning them releases toxic gases.
(4) Harmful non-biodegradable substances may cause diseases in living organisms.
In simple words: They do not rot, so they pile up and poison.

Teacher's Note:
1. Give at least three problems.
2. This is an NCERT question.

Question 12. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
(1) By separating biodegradable substances from non-biodegradable substances.
(2) By putting biodegradable organic waste into compost pits dug in the ground and preparing compost.
Recycling and reuse are other methods.
In simple words: Separate the waste and compost the wet waste.

Teacher's Note:
1. Two clear methods are enough.
2. Segregation is the first step.

Question 13. Write the essential functions performed by ozone at the higher levels of the Earth’s atmosphere? How is it produced? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced?
Answer:
Function: the ozone layer absorbs most of the harmful ultraviolet radiation of the Sun.
Production: high up in the atmosphere UV radiation splits oxygen molecules into atoms (O₂ → O + O), and each atom joins an oxygen molecule (O + O₂ → O₃).
Chemicals: chlorofluorocarbons (CFCs).
Reducing their use: replace CFCs with hydrochlorofluorocarbons, which break down more quickly, and dispose of old refrigerators and freezers safely.
In simple words: Ozone blocks UV, UV makes ozone from oxygen, and CFCs destroy it.

Teacher's Note:
1. Give all four parts of the answer.
2. Write the reactions in the correct direction.

Teacher's Note:
1. Write at least three points.
2. Give examples.

Question 15. What is a food web? Give few characteristics of a food web? Give an example of a food web?
Answer:
A food web is a network of food chains interconnected at various trophic levels, forming a number of feeding connections among the different organisms of a biotic community.
Characteristics: (1) it is an interlink of different food chains; (2) it provides alternative pathways of food availability; (3) due to greater alternatives for food, it makes the ecosystem stable; (4) it helps in the development of an ecosystem.
Example: Grass → Grasshopper → Frog → Snake → Hawk; Grass → Rabbit → Snake; Grass → Mouse → Hawk. These chains share organisms and form a web.
In simple words: A web of many food chains makes the ecosystem steadier.

Teacher's Note:
1. Give at least three characteristics.
2. Draw or write at least three connected chains.

Question 16. Answer the following:
(i) What is meant by non-biodegradable waste? Identify non-biodegradable wastes from the following: Empty packet of chips, empty plastic bottle of mineral water, empty paper box of sweets, empty tin of cold drink.
(ii) Pesticides added to the field are seen in increased amounts in the crop and in the birds that feed on them. What is this phenomenon called?
(iii) Which gas shields the surface of the earth from the harmful UV radiations from the sun?
(iv) Name the group of chemical compounds which adversely affect the ozone layer?
Answer:
(i) Substances that cannot be degraded naturally by microbes and persist in the environment for a long time are non-biodegradable. From the list: the empty packet of chips, the empty plastic bottle and the empty tin are non-biodegradable.
(ii) Biological magnification.
(iii) Ozone gas.
(iv) Chlorofluorocarbons (CFCs).
In simple words: Plastic and metal waste persists, pesticides magnify, ozone shields and CFCs harm it.

Teacher's Note:
1. Answer each part in one line.
2. The paper box is biodegradable.

Question 17. (a) From the following group of organisms create a food chain which is most advantageous for human beings in terms of energy. Hawk, Rat, Cereal plant, Goat, Snake, Human being
(b) State the possible disadvantage if the cereal plant is growing in soil rich in pesticides.
(c) Construct a food web using the organisms mentioned above.
Answer:
(a) Cereal plant → Human being, because the shortest chain loses the least energy.
(b) The cereal plant absorbs the pesticides from the soil with water and minerals. They pass to the animals and humans that eat it, and increase in concentration at each trophic level (biological magnification).
(c) Food web: Cereal plant → Rat → Snake → Hawk; Cereal plant → Goat → Human being; Cereal plant → Human being.
In simple words: The shortest chain gives the most energy, but pesticides in the soil reach the top.

Teacher's Note:
1. Write the food web as separate linked chains.
2. A frequent board question.

Question 18. (a) Create a food chain of the following organisms. Insect, Hawk, Grass, Snake, Frog
(b) Name the organism at the third trophic level of the created food chain.
(c) Which organism of this food chain will have the highest concentration of non-biodegradable chemicals?
(d) Name the phenomenon associated with it.
(e) If 10,000 Joules of energy is available to frogs, how much energy will be available to snakes in this food chain?
Answer:
(a) Grass → Insect → Frog → Snake → Hawk.
(b) The frog.
(c) The hawk, being the top consumer.
(d) Biological magnification.
(e) 10% of 10,000 J = 1000 J.
In simple words: Order the chain, count the levels and apply 10%.

Teacher's Note:
1. Frog = third trophic level.
2. Snakes are the next level after frogs.

Question 19. “Industrialization is one of the main cause of deterioration of environment.” List any four reasons in favour of this statement.
Answer:
(1) Industries release harmful gases which cause air pollution.
(2) Effluents from industries flow into rivers and lakes and cause water pollution.
(3) Big machines produce a lot of noise (noise pollution).
(4) Harmful chemicals and toxic wastes released into the soil reduce soil fertility (soil pollution).
In simple words: Industries pollute air, water, soil and sound.

Teacher's Note:
1. One point for each kind of pollution.
2. Name the pollutant for each.

Question 20. Give one example each from your daily life where the domestic waste can be effectively reused and recycled.
Answer:
Reuse: plastic and glass jars of jam and pickles can be reused to store salt, sugar or tea.
Recycle: old newspapers, some plastics, broken glass and metal wares can be recycled to make fresh paper, plastic, glass and metal objects.
In simple words: Reuse a jar as it is; recycle waste into a new product.

Teacher's Note:
1. Reuse means using the same item again; recycling makes a new product.
2. Name one example for each.

Question 21. (i) What is ‘environmental pollution’? (ii) Distinguish between biodegradable and non-biodegradable pollutants. (iii) Choose the non-biodegradable pollutants from the list given below: Paper, DDT, Radioactive waste, Plastic, Insecticides.
Answer:
(i) Environmental pollution is an undesirable change in the physical, chemical or biological characteristics of the natural environment, brought about by man’s activities, which may affect the soil, water or air.
(ii) Biodegradable pollutants can be broken down into harmless substances by microorganisms, are recycled and cause little pollution. Non-biodegradable pollutants cannot be broken down by microbes, persist for a long time and cause more pollution.
(iii) DDT, radioactive waste, plastic and insecticides are non-biodegradable. Paper is biodegradable.
In simple words: Pollution is harmful change; DDT, plastic and similar things do not rot.

Teacher's Note:
1. Pick all four non-biodegradable items.
2. Paper rots, so it is the odd one out.

Question 22. Give some methods that could be applied to reduce accumulation of pesticides in our body.
Answer:
(1) Minimise the use of pesticides in farming and use organic manure and biopesticides.
(2) Wash fruits and vegetables well before eating.
(3) Develop vegetarian food habits, since plants belong to a lower trophic level and have less accumulation of pesticides than animals of higher trophic levels.
In simple words: Use fewer pesticides, wash food and eat lower in the food chain.

Teacher's Note:
1. Link the third point to biomagnification.
2. Give at least two methods.