CBSE Class 10 Science Our Environment Sure Shot Questions Set 02

CBSE Class 10 Science Chapter 15 Our Environment assignment questions set 2 with answers. This page covers ecosystems, food chains and food webs, trophic levels and the 10 per cent energy rule, biomagnification, ozone depletion, biodegradable and non-biodegradable wastes, decomposers, eco-friendly habits, waste management in fertiliser industries, and the activity based questions on terrestrial and marine food chains, with the crossword on energy and environment.

ASSIGNMENT QUESTIONS SET - 2 CHAPTER - 15 OUR ENVIRONMENT

1. Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest

Answer: (b) Crop field

Teacher's Note:
a) A crop field is created and maintained by people through sowing, irrigation and weeding.
b) Pond, lake and forest develop naturally without human control.

2. In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers

Answer: (a) carnivores

Teacher's Note:
a) Producers form the first trophic level and herbivores the second.
b) Decomposers are not a part of the feeding levels of a food chain.

3. An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects

Answer: (c) both living organisms and non-living objects

Teacher's Note:
a) An ecosystem is the community of living organisms together with their physical surroundings.
b) The non-living part is called the abiotic component.

4. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk

(a) 5 kJ
(b) 50 kJ
(c) 500 kJ
(d) 5000 kJ

Answer: (d) 5000 kJ

1. Grass is the producer (first trophic level) and snake is at the fourth trophic level.
2. Only 10% of energy passes to the next level, so energy at the third level = 5 × 10 = 50 kJ.
3. Energy at the second level = 50 × 10 = 500 kJ.
4. Energy at the producer level = 500 × 10 = 5000 kJ.

Teacher's Note:
a) Each step up the chain loses about 90% of the energy, so the energy goes down tenfold at each level.
b) Count the levels from the producer, not from the top predator.

5. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as
(a) eutrophication
(b) pollution
(c) biomagnification
(d) accumulation

Answer: (c) biomagnification

Teacher's Note:
a) Non-biodegradable pesticides are stored in fat and are not excreted, so they build up at each level.
b) Top carnivores such as eagles receive the highest concentration.

6. Depletion of ozone is mainly due to
(a) chlorofluorocarbon compounds
(b) carbon monoxide
(c) methane
(d) pesticides

Answer: (a) chlorofluorocarbon compounds

Teacher's Note:
a) CFCs release chlorine atoms in the stratosphere, which break down ozone molecules.
b) Use of CFCs in refrigerators and aerosols was restricted under the Montreal Protocol.

7. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores

Answer: (b) producers

Teacher's Note:
a) Green plants and blue green algae are producers because they perform photosynthesis.
b) The radiant energy is the sunlight, which is trapped as chemical energy in food.

8. In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of
(a) heat energy
(b) light energy
(c) chemical energy
(d) mechanical energy

Answer: (c) chemical energy

Teacher's Note:
a) The energy passed on is stored in the body of the organism as food, which is chemical energy.
b) Most of the remaining 90% is lost as heat through respiration.

9. Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
(a) food web
(b) ecological pyramid
(c) ecosystem
(d) food chain

Answer: (a) food web

Teacher's Note:
a) A food web is a network of many interlinked food chains.
b) A food chain shows only one path of feeding.

10. Flow of energy in an ecosystem is always
(a) unidirectional
(b) bidirectional
(c) multi directional
(d) no specific direction

Answer: (a) unidirectional

Teacher's Note:
a) Energy enters from the sun and flows from producers to consumers and is lost as heat.
b) Energy cannot return to the sun, while nutrients are recycled.

11. Excessive exposure of humans to UV-rays results in
(i) damage to immune system
(ii) damage to lungs
(iii) skin cancer
(iv) peptic ulcers

(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)

Answer: (c) (i) and (iii)

Teacher's Note:
a) UV rays damage the DNA of skin cells, which can cause skin cancer.
b) Excess UV exposure also weakens the immune system, while peptic ulcers are not caused by UV rays.

12. In the following groups of materials, which group (s) contains only non-biodegradable items?
(i) Wood, paper, leather
(ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass
(iv) Plastic, bakelite, DDT

(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)

Answer: (b) (iv)

Teacher's Note:
a) Plastic, bakelite and DDT cannot be broken down by microorganisms.
b) Wood, paper, leather and grass are biodegradable, so group (i) and (iii) are wrong.

13. Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy at higher trophic levels
(b) Sufficient food supply
(c) Polluted air
(d) Water

Answer: (a) Decrease in energy at higher trophic levels

Teacher's Note:
a) Since only about 10% of energy passes up each level, very little energy is left after four or five levels.
b) This is why food chains are usually short.

14. Which of the statement is incorrect?
(a) All green plants and blue green algae are producers
(b) Green plants get their food from organic compounds
(c) Producers prepare their own food from inorganic compounds
(d) Plants convert solar energy into chemical energy

Answer: (b) Green plants get their food from organic compounds

Teacher's Note:
a) Green plants take in carbon dioxide and water, which are inorganic, and make glucose.
b) Plants make their own organic food, so they do not need organic compounds from outside.

15. Which group of organisms are not constituents of a food chain?
(i) Grass, lion, rabbit, wolf
(ii) Plankton, man, fish, grasshopper
(iii) Wolf, grass, snake, tiger
(iv) Frog, snake, eagle, grass, grasshopper

(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iv)

Answer: (a) (i) and (iii)

Teacher's Note:
a) Lion, wolf and tiger are top carnivores that do not feed on each other in a single chain.
b) Group (iv), grass to grasshopper to frog to snake to eagle, is a proper food chain.

16. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about
(a) 1%
(b) 5%
(c) 8%
(d) 10%

Answer: (a) 1%

Teacher's Note:
a) Only about 1% of the sunlight reaching plants is used in photosynthesis.
b) Much of the light is reflected, transmitted or used for heating.

17. In the given below Figure the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

[Figure: Pyramid of four stacked blocks. From the top: T4 (smallest), T3, T2, and T1 at the bottom (largest).]

(a) T4
(b) T2
(c) T1
(d) T3

Answer: (c) T1

Teacher's Note:
a) T1 is the producer level, which receives energy directly from the sun.
b) Energy decreases at each higher level, so the top level T4 has the least.

18. What will happen if deer is missing in the food chain given below?
Grass → Deer → Tiger

(a) The population of tiger increases
(b) The population of grass decreases
(c) Tiger will start eating grass
(d) The population of tiger decreases and the population of grass increases

Answer: (d) The population of tiger decreases and the population of grass increases

Teacher's Note:
a) Without deer, the tiger loses its main food and its population falls.
b) Without deer eating grass, the grass population rises.

19. The decomposers in an ecosystem
(a) convert inorganic material to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not breakdown organic compounds

Answer: (b) convert organic material to inorganic forms

Teacher's Note:
a) Decomposers such as bacteria and fungi break down dead organic matter into simple inorganic substances.
b) These substances return to the soil and are reused by plants.

20. If a grass hopper is eaten by a frog, then the energy transfer will be from
(a) producer to decomposer
(b) producer to primary consumer
(c) primary consumer to secondary consumer
(d) secondary consumer to primary consumer

Answer: (c) primary consumer to secondary consumer

Teacher's Note:
a) The grasshopper is a herbivore, so it is the primary consumer.
b) The frog eats the grasshopper, so it is the secondary consumer.

21. Disposable plastic plates should not be used because
(a) they are made of materials with light weight
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials

Answer: (d) they are made of non-biodegradable materials

Teacher's Note:
a) Non-biodegradable plates stay in the environment for many years and fill landfills.
b) Many of them are thrown into drains or eaten by animals.

22. Why is improper disposal of waste a curse to environment?

Answer:
1. Non-biodegradable waste remains in soil and water for a long time and pollutes them.
2. Waste heaps and stagnant water breed flies, mosquitoes and microbes that spread diseases.
3. Animals that eat waste, such as cows, can die after swallowing plastic.

Teacher's Note:
a) Waste blocks drains and causes flooding in the rainy season.
b) Burning plastic waste releases harmful gases into the air.

23. Write the common food chain of a pond ecosystem.

Answer: Phytoplankton → Zooplankton → Small fish → Large fish

Teacher's Note:
a) Phytoplankton are the producers of the pond.
b) Zooplankton are the herbivores that feed on them.

24. What are the advantages of cloth bags over plastic bags during shopping?

Answer:
1. Cloth bags can be reused many times, so they reduce waste.
2. They are biodegradable and do not block drains or harm animals.
3. They are stronger and can carry heavier loads.

Teacher's Note:
a) A cloth bag used for a few years costs less than buying plastic bags again and again.
b) Plastic bags are made from non-renewable petroleum.

25. Why are crop fields known as artificial ecosystems?

Answer: Crop fields are created and maintained by humans, who select the crop, add fertilisers, irrigate the land and remove weeds and pests. The natural balance is therefore controlled by people.

Teacher's Note:
a) In a natural ecosystem, the balance is maintained by nature alone.
b) Removing the crop and leaving the field would allow a natural ecosystem to develop.

26. Differentiate between biodegradable and non-biodegradable substances. Cite examples.

Answer:

Teacher's Note:
a) Biodegradable waste can be composted at home.
b) Non-biodegradable waste should be reduced, reused and recycled.

27. Suggest one word for each of the following statements/definitions
(a) The physical and biological world where we live in
(b) Each level of food chain where transfer of energy takes place
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
(d) Organisms which depend on the producers either directly or indirectly for food

Answer:
(a) Environment
(b) Trophic level
(c) Abiotic components
(d) Consumers

Teacher's Note:
a) The environment includes all living and non-living things around us.
b) Consumers include herbivores, carnivores and omnivores.

28. Explain the role of decomposers in the environment?

Answer:
1. Decomposers such as bacteria and fungi break down dead plants, dead animals and waste products.
2. They convert complex organic matter into simple inorganic substances.
3. These substances return to the soil and water, and plants use them again, which keeps the nutrient cycle going.

Teacher's Note:
a) Without decomposers, dead matter would pile up everywhere.
b) Decomposition also helps in making compost from farm waste.

29. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?

Answer:
1. A pond or lake is a natural ecosystem, where decomposers and natural water flow remove and recycle the waste.
2. An aquarium is an artificial closed system with few decomposers and no natural inflow of water.
3. Uneaten food and fish waste accumulate in the aquarium and harm the fish, so it must be cleaned.

Teacher's Note:
a) Natural ecosystems have a large number of organisms that keep the balance.
b) Cleaning the aquarium also keeps the water oxygen level high for the fish.

30. Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.

Answer:
1. Energy flows as: Sun → Producers → Primary consumers → Secondary consumers → Decomposers.
2. At each step, most of the energy is lost as heat through respiration and cannot be reused.
3. Energy therefore moves in one direction only and cannot return to the sun or the producers, which is why it is unidirectional.

Teacher's Note:
a) Unlike nutrients, which are recycled, energy is not recycled in the ecosystem.
b) The sun is the only source of energy for almost all ecosystems.

31. What are decomposers? What will be the consequence of their absence in an ecosystem?

Answer:
1. Decomposers are organisms such as bacteria and fungi that break down dead plants, dead animals and waste into simple substances.
2. In their absence, dead matter would accumulate, and nutrients would stay locked in it.
3. The soil would lose its fertility, plants would not get nutrients, and the whole ecosystem would collapse.

Teacher's Note:
a) Decomposers are the last link of every food chain.
b) Mushrooms and moulds are examples of fungal decomposers.

32. Suggest any four activities in daily life which are eco-friendly.

Answer:
1. Using cloth bags instead of plastic bags.
2. Planting trees and saving water.
3. Using public transport, cycling or walking instead of private vehicles.
4. Separating biodegradable and non-biodegradable waste at home.

Teacher's Note:
a) Small daily habits add up to a large saving of resources.
b) Using CFL or LED bulbs also saves electricity.

33. Give two differences between food chain and food web.

Answer:
1. A food chain is a single straight path of feeding, while a food web is a network of many interlinked food chains.
2. A food chain has fewer organisms, while a food web has many organisms and more alternative paths.

Teacher's Note:
a) A food web is more stable because if one prey species falls, the predator has other options.
b) Food chains are easy to draw but do not show the real feeding relationships.

34. Name the wastes which are generated in your house daily. What measures would you take for their disposal?

Answer:
1. Wastes generated daily include vegetable peels, leftover food, paper, plastic bags, bottles, glass, old clothes and used batteries.
2. Biodegradable wastes such as peels and leftover food should be composted or given to a compost pit.
3. Paper, plastic, glass and metal should be sold to the recycler, and used batteries and e-waste should be handed over to the authorised collection centre.

Teacher's Note:
a) Keep separate bins for wet and dry waste to make recycling easy.
b) Never throw batteries in the dustbin because they contain harmful metals.

35. Suggest suitable mechanism(s) for waste management in fertiliser industries.

Answer:
1. Treat the liquid effluents in an effluent treatment plant before they are released into water bodies.
2. Recover useful by-products, such as gypsum, from the waste and use them in other industries.
3. Use scrubbers and filters to clean the gases before they go into the air, and store solid waste in a safe, lined landfill.

Teacher's Note:
a) Recycling water within the plant reduces both pollution and water use.
b) Regular monitoring of the effluent helps to check that the limits set by the pollution control board are met.

36. What are the by-products of fertiliser industries? How do they affect the environment?

Answer:
1. By-products include phosphogypsum (solid waste), fluorides and fluorosilicic acid (in liquid effluent), and gases such as sulphur dioxide and hydrogen fluoride.
2. Fluoride and acid in effluents pollute water and harm fish and aquatic plants.
3. Gases released into the air cause acid rain and respiratory problems, and solid waste piles occupy land and can contaminate soil.

Teacher's Note:
a) Gypsum and fluorides build up in soil if the waste is dumped without treatment.
b) Excess fluoride in drinking water can cause fluorosis, which affects bones and teeth.

37. Explain some harmful effects of agricultural practices on the environment.

Answer:
1. Excessive use of chemical fertilisers makes soil less fertile and pollutes ground water and nearby ponds, which leads to eutrophication.
2. Pesticides kill useful insects such as bees and earthworms, and they accumulate through biomagnification in food chains.
3. Monoculture reduces biodiversity, while excessive irrigation causes waterlogging and soil salinity.
4. Burning crop residue releases smoke and pollutes the air.

Teacher's Note:
a) Use of organic manure and crop rotation reduces the need for chemical fertilisers.
b) Integrated pest management keeps pesticide use low.

38. ACTIVITY BASED QUESTION: Given below is the pictorial representation of a terrestrial food chain and a marine chain. Observe them carefully and answer the questions given in the worksheet.

[Figure: Two food chains side by side. Left, a terrestrial food chain from the bottom: Plant (primary producers), Herbivore (insect), a box labelled 1 with a rat picture, Carnivore with a snake, and Carnivore with an eagle at the top. The levels on the left are Primary producers, Secondary consumers and Tertiary consumers, and Quaternary consumers is at the top. A blank labelled 2 sits between the Herbivore and the rat level. Right, a marine food chain from the bottom: Phytoplankton (primary producers), Zooplankton, Carnivore (small fish), Carnivore (large fish), and Carnivore (orca) at the top.]

(i) Fill in the blank in the terrestrial food chain (Blank no. 1). Why is the rat given this term?

Answer:
1. Blank 1 is Carnivore.
2. The rat feeds on the herbivore (insect) below it, so it is a carnivore at the secondary consumer level.

Teacher's Note:
a) A carnivore eats animals, and the rat takes its energy from the herbivore.
b) The rat is in turn eaten by the snake, which is why it is placed in the middle of the chain.

(ii) Can the rat come at a lower position in the terrestrial food chain? Give reasons for your answer.

Answer: No. In this chain the rat eats herbivores, so it must be at a level above the herbivore. A rat can occupy a lower level only in another chain where it eats plants, and then it is a herbivore.

Teacher's Note:
a) The position of an organism depends on what it eats in that particular chain.
b) Rats are omnivores, so they can feed at more than one level.

(iii) Fill up the blank no. 2. Write one common feature of all organisms that are placed at this level in a food chain.

Answer:
1. Blank 2 is Primary consumers (herbivores).
2. All organisms at this level feed directly on producers such as plants or phytoplankton.

Teacher's Note:
a) Zooplankton in the marine chain are at the same level as the herbivore in the terrestrial chain.
b) Primary consumers are the first link between producers and animals.

(iv) What will be the fate of this terrestrial food chain if all the rats were removed?

Answer:
1. The snake, which eats rats, will lose its food and its population will fall.
2. The herbivores (insects) will increase because their predator is removed.
3. The increased herbivores will eat more plants, so the plant population will fall and the chain will be disturbed.

Teacher's Note:
a) Removing one level affects the levels above and below it.
b) The chain may become unstable until another food source is found.

(v) Will the food chains be affected if the animals at the top carnivore level were removed? Give reasons for your answer.

Answer: Yes, but the effect is smaller. Removing the top carnivores (eagle and large fish) lets their prey, such as snakes and small fish, increase. These prey then eat more of the level below, and the chain is disturbed until a new balance is reached.

Teacher's Note:
a) Top carnivores control the population of the species below them.
b) Without them, the chain may have many more middle level animals.

39. Name four biotic and four abiotic components observed in this area.

[Figure: The picture of the area referred to in questions 39 to 43 is not included in this PDF - add image.]

Answer:
1. Biotic components, for a typical field area: plants, insects, birds and earthworms.
2. Abiotic components: sunlight, water, air and soil.

Teacher's Note:
a) Biotic components are the living organisms, and abiotic components are the non-living factors.
b) Check these against the picture once it is added, since the area is not visible in this PDF.

40. Will this place be called a natural ecosystem or an artificial ecosystem? Give reasons for your answer.

Answer: It is an artificial ecosystem, because it is a managed area where humans control the plants and animals, for example through cultivation and the removal of weeds.

Teacher's Note:
a) A natural ecosystem is not managed by people.
b) This answer assumes that the area is a cultivated or managed field, as the picture is not included in this PDF.

41. List four producers and four consumers present in this area.

[Figure: The picture of the area referred to in questions 39 to 43 is not included in this PDF - add image.]

Answer:
Producers: grass, wheat, mango tree, algae.
Consumers: grasshopper, rat, sparrow, human beings.

Teacher's Note:
a) Producers are green plants that make food by photosynthesis.
b) Consumers depend on other organisms for food, so they are not producers.

42. Construct one food chain that operates in this area. Identify the producers, primary consumers, secondary consumers and tertiary consumers (if any) in the food chain.

[Figure: The picture of the area referred to in questions 39 to 43 is not included in this PDF - add image.]

Answer:
Grass → Grasshopper → Frog → Snake
Producer: grass. Primary consumer: grasshopper. Secondary consumer: frog. Tertiary consumer: snake.

Teacher's Note:
a) Each arrow shows the direction of energy flow from the eaten to the eater.
b) The snake is a tertiary consumer because it is the third consumer in this chain.

43. Write any two points of environmental concern that have arisen in the area due to human intervention.

[Figure: The picture of the area referred to in questions 39 to 43 is not included in this PDF - add image.]

Answer:
1. Use of chemical fertilisers and pesticides pollutes the soil and water.
2. Loss of trees and natural habitat reduces biodiversity.

Teacher's Note:
a) Human activities such as cutting trees and dumping waste affect the whole ecosystem.
b) These points are general and should be checked against the area shown in the picture.

44. Instruction: Read the clues given below and fill up the blocks with appropriate word/term to compete the crossword puzzle given below: One 'word' has been done for you.

Across:
3. This principle is useful in solar cooker but can be harmful on earth (5, 5, 6)
5. Element used to make solar cells
6. A black surface ____________ heat.
7. This fossil fuel made industrial revolution possible
8. A green house gas
10. High rise structures constructed on rivers to produce hydro electricity.

Down:
1. Its construction, on River Ganga, was opposed
2. Clean Fuel (abbreviation)
3. Bio-gas is commonly called
4. Nuclear power generation is based on this process
9. This energy is converted to electrical energy in a thermal power plant

Answer:
Across: 3. GREEN HOUSE EFFECT; 5. SILICON; 6. ABSORBS; 7. COAL; 8. METHANE; 10. DAM.
Down: 1. TEHRI (Tehri Dam); 2. CNG; 3. GOBAR GAS; 4. FISSION; 9. HEAT.

Teacher's Note:
a) The greenhouse effect traps heat that enters a closed space, so it is useful in a solar cooker but harmful on earth.
b) The Tehri Dam on the Bhagirathi, a source of the Ganga, faced strong opposition from environmentalists.

Question. Which of the following statements is incorrect?
(a) A food chain is always straight.
(b) Producers belong to second trophic levels.
(c) Top carnivore are fourth order consumers.
(d) Consumers obtain organic nutrients from outside as food.
Answer. A

Question. Select the mismatched pair.
(a) Crop field – Natural ecosystem
(b) Garden – Man made ecosystem
(c) Temperature – Abiotic factor
(d) Grass – Transducer
Answer. B

Question. DDT was accidently added to the water of a lake. All the organisms in it would be affected by DDT. Which of the following organisms would be affected the most?
(a) Man
(b) Birds living in the lake
(c) Fish living in the lake
(d) Aquatic plants in the lake
Answer. A

Question. The thinning of ozone layer was first observed in
(a) 1980s
(b) 1950s
(c) 1940s
(d) 1990s.
Answer. A

Question. Ozone layer is essential because it absorbs most of the
(a) infrared radiations
(b) solar radiations
(c) ultraviolet radiations
(d) both (a) and (b).
Answer. C

Question. Burning of waste substances usually in anaerobic conditions at high temperature of about 670°C is called
(a) land filling
(b) composting
(c) incineration
(d) none of these.
Answer. D

Question. Select the odd one out.
(a) Tomato leaves
(b) Wood
(c) Synthetic polymers
(d) Lime juice
Answer. C

Question. Complete the given analogy. Non-biodegradable : _________ :: Biodegradable : Livestock wastes
(a) Cotton
(b) Grass
(c) Glass
(d) Orange peel
Answer. C

Question. Which of the following groups contain nonbiodegradable substances only?
(a) Flowers, crops, plastic
(b) Plastic, polythene bags, aluminium cans
(c) Grass, wood, glass
(d) Fruit and vegetable peels, grass, wood
Answer. C

Question. Select the incorrect statement.
(a) Food we eat is digested by various enzymes in our body.
(b) Non-biodegradable substances are not broken down by biological processes.
(c) All enzymes have same action on each substance.
(d) Plastics cannot be broken down by the action of bacteria and other saprophytes.
Answer. B

Question. Minamata disease is due to
(a) MIC gas
(b) methyl mercury
(c) lead nitrate
(d) cobalt chloride.
Answer. D

Question. According to Charles Elton, which is not correct?
(a) Carnivores at the top of the pyramid.
(b) Producers at the top of the pyramid.
(c) Energy trapping is high at the top of the pyramid.
(d) Both (b) and (c)
Answer. D

Question. Which of the following statements regarding solid wastes is correct?
(a) Change in the packaging technology has resulted in generation of lot of solid wastes.
(b) Dumping of solid wastes could reduce the fertility of the soil leading to reduction in crop yield.
(c) Accumulation of solid waste could cause increased incidents of disease in a locality.
(d) All of these.
Answer. D

Question. Incineration and pyrolysis are two methods of waste disposal done at high temperature. The two differs from each other as in later
(a) aerobic burning occurs
(b) chemical energy and chemical constituents are recovered
(c) ashes are the end products
(d) medical wastes are burnt with clinkers as the end product.
Answer. B

Case I : Read the passage given below and answer the following questions.

Various components of an ecosystem maintain a balance in nature. Disturbance in any component of the environment cause an imbalance. One of the main environmental problem caused by human activities is global warming. Global warming is a phenomenon caused by the increasing concentration of greenhouse gases in the atmosphere resulting due to enhanced greenhouse effect.

Question. Refer to the given pie chart showing the contribution of different gases to global warming.

Identify gases P, Q, R and S and select the incorrect statement regarding them.
(a) P could be a gas that increases in atmosphere due to excessive use of fossil fuel.
(b) Q could be a gas produced by complete combustion of biomass.
(c) R could be synthetic gaseous compounds used as refrigerants in air conditioners and refrigerators.
(d) S could be a gas produced by combustion of nitrogen rich fuel.
Answer. B

Question. What could not be a source of gas Q given in the above pie chart?
(a) Flooded paddy field
(b) Cattle
(c) Jet fuel
(d) Marshes
Answer. C

Question. If there is no CO₂ in the atmosphere, then what will be the most likely consequence of this on the temperature of earth?
(a) The temperature remain unchanged as it depends upon the oxygen content of the atmosphere.
(b) The temperature would increase as less greenhouse gases will be absorbed by CO₂.
(c) The temperature would decrease as CO₂ is the principal greenhouse gas.
(d) None of these
Answer. C

Question. Study carefully the following figure representing greenhouse effect.

Select the correct statement regarding this.
(a) Much of the long wavelength infrared radiations re-radiated by the earth’s surface are absorbed by the atmospheric greenhouse gases.
(b) CO₂, CH₄, CFCs and N₂O are the gases which are responsible for greenhouse effect.
(c) The atmosphere is transparent to the incoming short-wavelength radiations and is translucent to the long-wavelength infrared radiations.
(d) All of these
Answer. D

Question. Greenhouse effect is due to
(a) accumulation of O₃ and depletion of CO₂
(b) accumulation of both O₃ and CO₂
(c) accumulation of CO₂ and depletion of O₃
(d) presence of green plants on the earth.
Answer. C

For question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Both assertion and reason are true, and reason is correct explanation of the assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Assertion is false, but reason is true.

Question. Assertion : The burning of substances at higher temperature to form ash is called incineration.
Reason : Incineration greatly reduces the volume of waste.
Answer. B

Question. Assertion : If pesticide is present in water bodies then fish eating birds accumulate maximum amount of DDT in their bodies.
Reason : Pesticides are not metabolised within bodies of living organisms and get concentrated at each trophic level leading to bioaccumulation.
Answer. A

Question. Assertion : Using jute bags while shopping is more environment friendly as compared to polythene bags.
Reason : Jute is biodegradable whereas polythene bag is non-biodegradable.
Answer. A

Question. Assertion : A food chain comprises of producers and consumers.
Reason : Consumers can be herbivores, carnivores and omnivores.
Answer. B

Question. Assertion : We live in troposphere.
Reason : Our atmosphere extends beyond troposphere also.
Answer. B

Question. We often use the word environment. What does it mean?
Answer. Environment can be defined as the physical or biological world where an organism lives. Literally speaking, an, organism’s immediate surrounding constitutes its environment which includes both biotic and abiotic components around it.

Question. Why is lake considered to be a natural ecosystem?
Answer. Lake is an ecosystem where living organisms grow, reproduce and interact among each other as well as with abiotic components and carry out other activities in nature by themselves without any human interference, therefore it is referred to as a natural ecosystem.

Question. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals?
Name the phenomenon associated with it.
Insects, Hawk, Grass, Snake, Frog
Answer. Among the following organisms of the food chain, hawk being top consumer is present at topmost trophic level, hence will have the highest concentration of non-biodegradable chemicals due to a phenomenon known as biomagnification.

Question. In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer?
Answer. According to ten percent law, 10% of the energy of producer will be available to primary consumer, and 10% of this energy will be available to secondary consumer (100J) and so on.

Question. Why is excessive use of CFCs a cause of concern?
Answer. CFCs or chlorofluorocarbons are potent compounds that release active chlorine in the atmosphere which reacts with ozone molecules present there to convert them to oxygen.This results in thinning of ozone layer. Hence, excessive use of CFCs is a cause of concern.

Question. Why only 4 or 5 trophic levels are present in each food chain?
Answer. The quantum of available energy in a food chain successively gets decreased at each trophic level. There is only 10% flow of energy from one trophic level to the next higher level. Second law of thermodynamics says that transformation of energy from one form to the other is inefficient and involves dissipation of unavailable energy. This loss of energy at successive trophic levels restricts the size of food chain in an ecosystem to maximum 4 to 5 steps. Hence, only 4 to 5 trophic levels are present in each food chain.

Question. Write three characteristics of energy transfer in the biosphere?
Answer. The following are the characteristics of energy transfer in the biosphere: (any three)
(i) Energy is supplied by the sun and it is not created in the biosphere. Energy is only converted from one form to another in the biosphere.
(ii) The flow of energy is unidirectional.
(iii) There is loss of energy as we go from one trophic level to the next in an ecosystem. At each transfer, generally 80-90% of energy is lost as heat in accordance with second law of thermodynamics.

Question. Mention the advantages of paper bags over plastic bags.
Answer. The advantages of paper bags over plastic bags are :
(i) Paper bags can be recycled as they are biodegradable Their recycling does not produce poisonous gases like recycling of plastic bags.
(ii) Once discarded, paper bags can be recycled again easily, while plastic bags cannot be recycled easily as they clog machines and complicate the recycling processes.
(iii) Plastic bags kill thousands of marine animals every year as some animals confuse plastic bags with jellyfish which block the entrance to the stomach. Paperbags are a healthy, safe alternative to hazardous plastic bags.
(iv) Paper bags are finding favour with all consumers, government and even the environmentalists.

Question. What will happen if all the deers are removed from the given food chain?
Plants → Deer → Tigers
Answer. From the given food chain, if the deers are removed, the population of plants will increase as deers are herbivores and feed on plants whereas the population of tiger (that consume deer) will decrease, as food available for tiger would be less.

Question. (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) A food chain which is most advantageous for human beings in terms of energy is:
Cereal plant → Human being
(b) If the cereal plant is growing in soil rich in pesticides, then these pesticides would be absorbed by growing plants along with water and minerals, when animals eat these cereal plants, these poisonous chemical pesticides go into their bodies through food. This increase in concentration of harmful pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification. Pesticides are lethal to non-target species also. The extensive use of pesticides in agriculture can change the community of microorganisms living in soil.

Question. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer. Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels, e.g., removal of all the producers (T1) will adversely affect all the types of consumers including herbivores and carnivores, while the removal of all the herbivores will adversely affect only the carnivores but there will be increase in the number of the producers.
No, Removal of all the organisms of any trophic level will always adversely affect the ecosystem, e.g., the removal of lions and tigers (top carnivores) will cause rapid increase in deer population, which will lead to rapid consumption of vegetation resulting in scarcity of vegetation and population crash of deer.

Question. Study the given food chain anddiscuss the effect of removal of any one of the trophic level from it.
Grasses → Deers → Lions
Answer. In the above food chain, if all the lions are removed,
the population of deer will increase since there would not be any lion to kill them and to keep the deer population under control. This will lead to high consumption of grasses (producers) and may even eliminate them and if the deer population is removed instead of lions, it will lead to decrease of lion population since there will not be any prey. The lions may even resort to other preys such as domestic animals or man to survive. If the deer and lion operate in other food chains in a food web, then the removal of any one of them will lead to disruption of the food web and will cause disturbance in the ecosystem. In addition if the grasses (producers) are removed, then all life will come to an end. If there is no grass, there will be no herbivores. If there are no herbivores, then there will be no carnivores. Therefore, ultimately all organisms will die.

Question. “Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues.”
State the reason to explain how and why it happens.
Answer. Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants along with water and other mineral’s. When herbivorous animals feed on these plants the poisonous pesticides enter their bodies through the food chain. Similarly, when the carnivorous animals eat these herbivores, the pesticides get transferred to their bodies. Therefore, the plant products such as food grains, vegetables and fruits as well as meat of animals contain varying amounts of pesticide residues depending upon the trophic level they occupy in a food chain.

Question. Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
Answer. Two harmful effects of using plastic bags on the environment:
(i) Plastic bags are non-biodegradable substances which are not acted upon by microbes. So, they cannot be decomposed and therefore persist in the environment for a long time causing harm to the soil fertility and quality.
(ii) Plastic bags choke drains which result in waterlogging, that allows breeding of mosquitoes and hence leads to various diseases.Jute bags and cloth bags are the alternatives to the polyethene bags.

Question. What do you mean by acid rain? Give some effective measures to control it.
Answer. Any precipitation or deposition having a pH lower than 5.6 is called acid rain. Acid rain occurs by the emission of sulphur dioxide and oxides of nitrogen that react with rain
water and form acids.
Following measures can be taken to prevent and control acid rain:
(i) Acid rain is mainly caused due to air pollution. Air pollution can be reduced by using pollution-controlling equipment, such as scrubber.
(ii) Other sources for the generation of electricity, such as nuclear fuel or solar power can be used instead of using fossil fuel to reduce the release of oxides of nitrogen and sulphur.
(iii) Cleaner fuels, such as LPG, CNG, etc., could be used in automobiles.
(iv) Use of neutralising agents such as powdered lime stone can be sprayed over areas that are prone to acid rain.

Question. Give suitable mechanism(s) for waste management in fertiliser industries.
Answer. Industries involved in making inorganic fertilisers such as urea, potash, etc., cause air and water pollution by releasing harmful and toxic chemicals in air and water during the synthesis of the chemical fertilisers.
Measures required to be adopted for the management of these wastes are :
(i) The release of various pollutants directly in the air should be controlled and minimised by removing particulate matter and gaseous pollutants from foul air before its emission in the source.
(ii) The effluents should be treated and then discharged into the environment. Before discharging them in the water source they should be converted into less harmful, non-toxic materials.

Question. What efforts have been made at international level for mitigating global change?
Answer. Initiatives for mitigating global change are: Montreal Protocol (16 September 1987) : A landmark international agreement to protect the stratospheric ozone by agreeing to limit the production and use of ozone depleting substances to half the level of 1986 and helping the developing countries to implement use of alternatives to CFCs.
Helsinki Declaration (May, 1989) : Montreal Protocol was ratified by 82 nations at Helsinki. They pledged to phase out CFCs by 2000.
Kyoto Protocol (December, 1997) : International conference held in Kyoto, Japan obtained commitments from different countries for developing alternatives to oxygen depleting substances (ODS) and reducing overall greenhouse gas emissions at a level 5% below 1990 level by 2008-2012. Beijing Protocol (1999) – The protocol lays down steps to reduce emission of CFCs and other ozone depleting substances. It separates the efforts to be made by developing and developed countries.

Question. What will be the consequence of absence of decomposers in an ecosystem?
Answer. In absence of decomposers, recycling of materials will not occur in biosphere. It is due to the reason that decomposers break down the complex organic substances like dead organisms, garbage, etc. into simple inorganic compounds, which go into the soil and used again by plants. From plants they enter the biosphere through food chain.

Question. State the consequences of stratospheric zone depletion.
Answer. Stratosphere contains ozone layer which absorbs harmful UV radiations of the sun, protecting the living beings on earth from health consequences of stratospheric zone (ozone) defetion are:
(i) Cancers: UV radiations damage skin cells causing increase in incidences of skin cancer and skin ageing.

Question. Length of food chains in an ecosystem is generally limited to three or four trophic levels. Why?
Answer. Energy flow is always unidirectional, moving successively through trophic levels. Solar energy is received and trapped by autotrophs which passes it to primary, secondary and tertiary consumers. During energy transfer from one trophic level to successive trophic level, 90% of energy is lost and only 10% energy reaches the next trophic level, (Lindemann’s 10% law). Thus, after three or four trophic levels, negligible amount of energy is left to be passed to the next trophic levels. That is why length of food chains is limited to three or four trophic levels only. According to 10% law: If a producer produces 1000 KJ energy, then T2 level (second trophic level) will get 100 KJ, T3 will get 10 KJ of energy, T4 will get 1 KJ and for T5 0.1 KJ energy will be left. More number of trophic levels will get further decreased amount of energy which is neither economical, nor feasible. Thus in nature, length of food chains is generally limited to three or four trophic levels.

Question. Name the wastes which are generated in your house daily. What measures would you take for their disposal?
Answer. The types of waste generated in a house are—
(i) Kitchen wastes like vegetable and fruit peel, rind, used tea leaves.
(ii) Empty milk pouches, polythene bags, empty cartons, etc.
(iii) Waste paper (newspaper, paper bags, packing paper).
(iv) Used tooth picks and ear buds.
(v) Dust and other sweepings.
Measures for household waste disposal–
At an individual’s end following measures should be taken:
(i) Reuse of maximum possible materials
(ii) Separation of biodegradable and non-biodegradable wastes
(iii) Biodegradable wastes should be used for composting
(iv) Non-biodegradable wastes should be disposed off at suitable places from where municipal authorities can pick them up and dispose properly and scientifically.

(a) 5 k J

(b) 50 k J

(c) 500 k J

(d) 5000 k J

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