Chapter 13: Our Environment

Multiple Choice Questions

1. Which one of the following is an artificial ecosystem?

(a) Pond       (b) Crop field          (c) Lake        (d) Forest

Answer: (b) Crop field:

[ A crop field is an example of an artificial ecosystem because it is created and maintained by human activities for the cultivation of crops, and it is not a naturally occurring ecosystem like a pond, lake, or forest.]

2. In a food chain, the third trophic level is always occupied by

(a) carnivores       (b) herbivores      (c) decomposers     (d) producers

Answer: (a) carnivores:

[ The third trophic level in a food chain is typically occupied by carnivores, which are organisms that consume other animals. ]

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 .

[ An ecosystem comprises both living organisms (biotic components) and non-living objects (abiotic components) in a specific area, interacting with each other and their environment.]

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 k J        (b) 50 k J      (c) 500 k J     (d) 5000 k J

Answer :  (d) 5000 kJ .

[ In a food chain, energy decreases as it moves up each trophic level due to energy loss at each step, typically around 10% efficiency. Given that the energy available at the fourth trophic level (Hawk) is 5 kJ, you can estimate the energy available at the producer level (Grass) by reversing this process:

Energy available at the fifth trophic level (Hawk) is 5 kJ.

Energy available at the fourth trophic level (Snake) is 10 times that of the Hawk, which is 5 kJ×10=50 kJ .

Energy available at the third trophic level (Frog) is 10 times that of the Snake, which is 50 kJ×10=500 kJ .

Energy available at the second trophic level (Grasshopper) is 10 times that of the Frog, which is 500 kJ×10=5000 kJ .

Energy available at the producer level (Grass) is 10 times that of the Grasshopper, which is 5000 kJ×10=50,000 kJ .]

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:

[ The accumulation of non-biodegradable pesticides in increasing amounts at each higher trophic level in the food chain is known as biomagnification. ]

6. Depletion of ozone is mainly due to

(a) chlorofluorocarbon compounds       (b) carbon monoxide

(c) methane                                           (d) pesticides

Answer :  (a) chlorofluorocarbon compounds:

[ Depletion of ozone is mainly attributed to the release of chlorofluorocarbon (CFC) compounds into the atmosphere, which break down ozone molecules in the stratosphere.]

7. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called

(a) decomposers        (b) producers      (c) herbivores        (d) carnivores

Answer : (b) producers

[ Organisms that synthesize carbohydrates from inorganic compounds using radiant energy (usually sunlight) through the process of photosynthesis are called producers. ]

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.

[ In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of chemical energy stored in organic compounds, such as glucose, that make up the bodies of organisms.]

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

[ Organisms of a higher trophic level that feed on several types of organisms belonging to a lower trophic level constitute a food web, which represents a complex network of interconnected food chains in an ecosystem.]

10. Flow of energy in an ecosystem is always

(a) unidirectional              (b) bidirectional

(c) multi directional          (d) no specific direction

Answer :  (a) unidirectional

[ The flow of energy in an ecosystem is typically unidirectional, meaning it moves through the trophic levels from producers to consumers and decomposers in one direction. ]

11. Excessive exposure of humans to U V-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)

[ Excessive exposure to UV rays can result in damage to the immune system and an increased risk of skin cancer.]

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: (d) (ii) and (iv)

[ Polythene, detergent, PVC, plastic, bakelite and DDT are all non-biodegradable materials, which do not easily break down in the environment. ]

13. Which of the following limits the number of trophic levels in a food chain?

(a) Decrease in energy at higher trophic levels

(b) Dufficient food supply

(c) Polluted air

(d) Water

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

[ The energy available to organisms decreases as it moves up the trophic levels in a food chain. This decrease in energy limits the number of trophic levels that can be supported in an ecosystem. ]

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.

[ This statement is incorrect. Green plants are producers that use photosynthesis to convert inorganic compounds (such as carbon dioxide and water) into organic compounds (like glucose) using solar energy.]

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:  (c) (ii) and (iii)

[ In the given options, plankton, man, fish, and grasshopper belong to different trophic levels and do not form a direct linear sequence in a traditional 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 %       

[ Only about 1% of the solar energy falling on the leaves of green plants is actually captured and used for photosynthesis. The rest is reflected, transmitted, or converted into heat. This 1% energy then gets transferred through different trophic levels in a food chain.]

17. In the given Figure 15.1 the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

       

(a)             (b)           (c)          (d)

Answer:  (c)

[ The trophic level at the base of the pyramid () typically has the maximum energy available, as it represents the primary producers (plants) that capture energy from the sun. ]

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

[ Without deer, the tiger's primary food source is missing, leading to a decrease in the tiger population and a potential increase in the grass population.]

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.

[ Decomposers break down organic material into simpler, inorganic compounds, facilitating the recycling of nutrients in an ecosystem by returning them to the soil.]

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.

[ Grasshopper (primary consumer → eats plants) is eaten by frog (secondary consumer). So energy transfers from primary to 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

[ Non-biodegradable plastics persist in the environment for a long time, contributing to pollution and harm to wildlife. Their disposal and accumulation pose significant environmental problems.]

Short Answer Questions

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

Answer: Improper disposal of waste is a curse to the environment because it causes air, water and soil pollution. It spreads diseases, produces foul smell and harms living organisms. Non-biodegradable wastes like plastics remain in the environment for a long time and disturb the ecological balance.

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

Answer:  A common food chain of a pond ecosystem is:

Aquatic plants (producers)→ Aquatic insects (primary consumer) → Fish (secondary consumer)→ Heron (tertiary consumer)

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

Answer :  Advantages of cloth bags over plastic bags during shopping are:

(i) Cloth bags are reusable and durable.

(ii) They are biodegradable and do not cause pollution.

(iii) They help in reducing plastic waste in the environment.

(iv) Cloth bags are eco-friendly and can be used many times

25. Why are crop fields known as artificial ecosystems?

Answer: Crop fields are called artificial ecosystems because they are created and maintained by humans for growing crops. They require regular human activities such as irrigation, use of fertilizers, pesticides and protection from weeds. Unlike natural ecosystems, crop fields cannot sustain themselves without human care and management.

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

Answer:  The difference between biodegradable and non-biodegradable substances :

Biodegradable	Non – Biodegradable
(i) Biodegradable substances can be broken down by natural processes, including the action of microorganisms, into simpler, non-toxic components. Examples: Food scraps, paper, wood, and natural fibers like cotton and wool.	(i) Non-biodegradable substances cannot be broken down easily by natural processes and persist in the environment for long periods. Examples: Plastics, synthetic fibers, metals, and glass.
(ii) They decompose naturally and integrate back into the environment without causing long-term pollution.	(ii) They remain in landfills or natural habitats, contributing to pollution and environmental harm.

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 (c) Abiotic (d) Consumers

28. Explain the role of decomposers in the environment ?

Answer: Decomposers such as bacteria and fungi break down dead plants, animals and organic wastes into simple substances. They recycle nutrients back to the soil and environment, helping in maintaining soil fertility. They also clean the environment by removing dead organic matter and support the continuous flow of nutrients in ecosystems.

29. Select the mis-matched pair in the following and correct it.

(a) Biomagnification — Accumulation of chemicals at the successive trophic levels of a food chain

(b) Ecosystem — Biotic components of environment

(c) Aquarium — A man-made ecosystem

(d) Parasites — Organisms which obtain food from other living organisms

Answer: The mis-matched pair is: (b) Ecosystem — Biotic components of environment
Ecosystem: The interaction between biotic components (living organisms) and abiotic components (physical factors like sunlight, water, soil, air, temperature, etc.) of the environment, functioning together as a unit.

All other pairs are correctly matched:

(a) Biomagnification is correctly defined.

(c) Aquarium is indeed a man-made ecosystem.

(d) Parasites correctly obtain food from other living organisms.

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

Answer: Ponds and lakes are natural ecosystems in which producers, consumers and decomposers maintain a natural balance. Decomposers clean the water by breaking down wastes and dead organisms. An aquarium is an artificial ecosystem where this balance is not complete. Therefore, wastes accumulate in it and it needs to be cleaned regularly.

Long Answer Questions

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

Answer: The flow of energy in an ecosystem takes place from the Sun to producers and then to consumers. Green plants capture solar energy and convert it into food. This energy is passed from producers to herbivores and then to carnivores through food chains.

Flow of energy in an ecosystem: Sun → Producers → consumers (Herbivores) → Carnivores

The flow of energy is called unidirectional because energy moves only in one direction and is not recycled back to the Sun or previous trophic levels. At each trophic level, some energy is lost as heat during various life processes. Therefore, energy continuously decreases as it moves through the ecosystem.

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

Answer: Decomposers are organisms such as bacteria and fungi that break down dead plants, animals, and organic wastes into simpler substances. They help in recycling nutrients back into the soil.

In the absence of decomposers, dead bodies and wastes would keep accumulating in the environment. Nutrients would not be returned to the soil, causing a shortage of nutrients for plants. As a result, the balance of the ecosystem would be disturbed and life processes in the ecosystem would be affected.

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

Answer: Four eco-friendly activities in daily life are :

(i) Using reusable bags for shopping to reduce plastic waste.

(ii) Walking, biking, or using public transportation instead of driving to decrease carbon emissions.

(iii) Conserving water by fixing leaks, taking shorter showers, and using water-efficient appliances.

(iv) Recycling paper, plastic, glass, and metal to minimize waste and conserve resources.

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

Answer:  Two differences between a food chain and a food web :

Food Chain	Food Web
It is a linear sequence showing a single pathway of energy flow from one organism to another.	It is a network of interconnected food chains showing multiple pathways of energy flow.
It is simple and involves one organism at each trophic level.	It is complex and involves many organisms at different trophic levels with interconnections.

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

Answer: The wastes generated daily in our house include vegetable peels, leftover food, paper, plastic bags, bottles, wrappers, old clothes and wastewater.

Measures for their disposal:

(i) Separate biodegradable and non-biodegradable wastes.

(ii) Prepare compost from kitchen wastes.

(iii) Reuse and recycle paper, plastic, glass and metal items.

(iv) Dispose wastes in covered dustbins.

(v) Avoid throwing garbage in open places or water bodies.

36. Suggest suitable mechanism (s) for waste management in fertilizer industries.

Answer: The suitable mechanisms for waste management in fertilizer industries are:

(a) Treatment of industrial wastes before releasing them into water bodies.

(b) Installation of effluent treatment plants .

(c) Recycling and reuse of chemicals and wastewater.

(d) Proper disposal of solid wastes in safe landfills.

(e) Use of pollution-control devices to reduce air pollution.

(f) Adoption of eco-friendly and cleaner production technologies.

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

Answer: The by-products of fertiliser industries include oxides of nitrogen and sulphur, along with various liquid chemicals and solid waste materials . These by-products have several harmful effects on the environment.

The oxides of nitrogen and sulphur released into the air mix with rainwater to form acids, leading to acid rain. This acid rain is highly destructive as it damages forests and crops, harms aquatic life in water bodies, and even corrodes historical buildings and monuments made of stone. Additionally, the liquid and solid chemical wastes from these industries can percolate through the soil, causing soil pollution and reducing soil fertility. If these liquid chemicals are discharged directly into rivers or lakes, they poison the water and cause the death of aquatic animals.

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

Answer:  Modern agricultural practices have several harmful effects on the environment:

(a) Excessive use of fertilisers reduces the fertility of soil and pollutes water bodies.

(b) Pesticides and insecticides contaminate soil and water and may harm useful organisms.

(c) Over-irrigation can cause waterlogging and increase salinity of soil.

(d) Deforestation for agriculture disturbs ecological balance and reduces biodiversity.

(e) Continuous use of chemicals may also affect human health through the food chain.