CBSE Class 10 Science Our Environment Sure Shot Questions Set 01

CBSE Class 10 Science Chapter 15 Our Environment Multiple Choice Questions 

Question. Abundance of coliform bacteria in a water body is indicative of pollution from
(A) petroleum refinery.
(B) metal smelter
(C) fertilizer factory
(D) domestic sewage.
Answer : D

Question. Prolonged exposure to the fumes released by incomplete combustion of coal may cause death of a human because of
(A) inhalation of unburnt carbon particles.
(B) continuous exposure to high temperature.
(C) increased level of carbon monoxide.
(D) increased level of carbon dioxide.
Answer : C

Question. Acid Rain is caused by :
(A) CO
(B) SO₂
(C) O₂
(D) All of the above
Answer : B

Question. Primary consumers form _____ trophic level.
(A) First
(B) Second
(C) Third
(D) Fourth
Answer : B

Question. Chipko andolan is associated with :
(A) Tomatoes
(B) Turtles
(C) Trees
(D) Lions
Answer : C

Question. The decomposers in an ecosystem convert
(A) Inorganic substance into organic substance
(B) Simpler substance into complex substance
(C) Solar energy into chemical energy
(D) Organic substance into inorganic substance
Answer : D

Question. In the given figure, various trophic levels are shown in the form of pyramid. At which trophic level the minimum energy is available ?

(A) Phytoplanktons
(B) Man
(C) Fish
(D) Zooplankton
Answer : B

ASSIGNMENT QUESTIONS SET - 1
CHAPTER - 15
OUR ENVIRONMENT

1. What percentage of sunlight is captured by plants to convert it into food energy?
(a) 1%
(b) 10%
(c) 50%
(d) more than 50%

Answer: (a) 1%

1. Green plants capture only a very small part of the sunlight falling on them.
2. Hence, the correct option is (a).

Teacher's Note:
a) Most sunlight is reflected, absorbed as heat or passes through the leaves unused.
b) Only about 1% is converted into food energy during photosynthesis.

2. Flow of energy in an ecosystem is always
(a) unidrectional
(b) bidrectional
(c) multidirectional
(d) none of these

Answer: (a) unidrectional

1. Energy enters the ecosystem as sunlight and is captured by producers.
2. It moves to consumers and is finally lost as heat; it never returns to the sun.
3. Hence, the correct option is (a).

Teacher's Note:
a) Energy flow is one way, but nutrients are recycled.
b) Heat lost at each trophic level cannot be reused by the ecosystem.

3. Which of the following is non-biodegradable?
(a) Tea leaves
(b) Nylon
(c) remains of animals
(d) fleece of sheep

Answer: (b) Nylon

1. Tea leaves, remains of animals and fleece of sheep are natural materials.
2. Decomposers break them down easily.
3. Nylon is a synthetic polymer that microorganisms cannot decompose.
4. Hence, the correct option is (b).

Teacher's Note:
a) Synthetic polymers such as nylon and polythene persist in the environment for years.
b) Natural fibres like wool are biodegradable.

4. The structural and functional unit of the environment is known as:
(a) ecosystem
(b) biosphere
(c) food chain
(d) food web

Answer: (a) ecosystem

1. An ecosystem includes living organisms and their non-living surroundings that interact with each other.
2. Hence, the correct option is (a).

Teacher's Note:
a) The biosphere is the sum of all ecosystems on earth.
b) A food chain or food web is only one part of an ecosystem.

5. Depletion of ozone layer is mainly due to
(a) Methane
(b) Carbon Dioxide
(c) ChloroFloroCarbons
(d) Nitrogen

Answer: (c) ChloroFloroCarbons

1. Chlorofluorocarbons (CFCs) release chlorine atoms in the upper atmosphere.
2. Chlorine atoms break down ozone molecules.
3. Hence, the correct option is (c).

Teacher's Note:
a) CFCs were used in refrigerators, air conditioners and aerosol sprays.
b) Carbon dioxide and methane are greenhouse gases, not the main cause of ozone loss.

6. First order consumers are:
(a) Carnivores
(b) Herbivores
(c) Decomposers
(d) Omnivores

Answer: (b) Herbivores

1. First order consumers feed directly on producers, the green plants.
2. Animals that eat only plants are herbivores.
3. Hence, the correct option is (b).

Teacher's Note:
a) First order consumers are also called primary consumers.
b) Carnivores are higher order consumers that eat other animals.

7. A detritus food chain begins with
(a) Carnivores
(b) Herbivores
(c) Omnivores
(d) Decomposers

Answer: (d) Decomposers

1. A detritus food chain starts from dead organic matter, called detritus.
2. Decomposers act on this detritus and are the first organisms in this chain.
3. Hence, the correct option is (d).

Teacher's Note:
a) Detritus food chains are common in forest floors and soil.
b) Grazing food chains begin with green plants, not decomposers.

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

Answer: (b) chemical energy

1. The 10% of energy that is passed on is stored in the body of the organisms as food.
2. Food energy is stored as chemical energy in organic compounds.
3. Hence, the correct option is (b).

Teacher's Note:
a) The remaining 90% is lost mainly as heat during respiration and metabolism.
b) Heat is not the energy that gets transferred to the next level.

9. 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

1. Non-biodegradable pesticides are not broken down and get stored in body fat.
2. Each predator eats many prey, so the concentration rises at each higher trophic level.
3. This increasing concentration is called biomagnification.
4. Hence, the correct option is (c).

Teacher's Note:
a) Eutrophication is excess nutrient enrichment of water bodies.
b) Top carnivores such as birds of prey are most affected.
c) Ordinary accumulation does not describe the rise across trophic levels.

10. Which of the following is an abiotic component
(a) plants
(b) animals
(c) soil
(d) microorganisms

Answer: (c) soil

1. Plants, animals and microorganisms are living, so they are biotic.
2. Soil is non-living, so it is abiotic.
3. Hence, the correct option is (c).

Teacher's Note:
a) Abiotic components include air, water, soil, light and temperature.
b) Living things are always biotic components.

11. 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

1. Green plants prepare food by photosynthesis from carbon dioxide and water.
2. These are inorganic raw materials, so option (b) is wrong.
3. Hence, the incorrect statement is (b).

Teacher's Note:
a) Producers make organic food from inorganic substances.
b) Plants do not take in ready-made organic food from outside.
c) Option (d) is correct because solar energy is stored as chemical energy in food.

12. Edaphic factors are included in
(a) Abiotic components
(b) Biotic components
(c) Producers
(d) Consumers

Answer: (a) Abiotic components

1. Edaphic factors are the soil-related factors such as soil texture, water content and minerals.
2. Soil is non-living, so these factors belong to the abiotic components.
3. Hence, the correct option is (a).

Teacher's Note:
a) Edaphic means relating to soil.
b) Climatic factors such as temperature and rainfall are also abiotic.

13. Only ____ % of the energy can be transferred from one trophic level to the next trophic level.
a) 1
b) 5
c) 10
d) 20

Answer: c) 10

1. According to the 10% law, only about 10% of energy passes to the next trophic level.
2. Hence, the correct option is c).

Teacher's Note:
a) The 10% law explains why food chains have only three or four levels.
b) The rest of the energy is lost as heat and in excretion.

14. Accumulation of non- biodegradable pesticides in different trophic levels is called
a) Biological degradation
b) Biological magnification
c) Biological concentration
d) Biological deposition

Answer: b) Biological magnification

1. Accumulation of non-biodegradable pesticides in increasing amounts across trophic levels is biological magnification.
2. Hence, the correct option is b).

Teacher's Note:
a) Biological magnification is the same process as biomagnification.
b) Biological degradation means breakdown, which is the opposite process.

15. The UV radiation from the sun is likely to cause _____________ in human.
a) Skin cancer
b) Lung cancer
c) Liver Cancer
d) Brain Cancer

Answer: a) Skin cancer

1. UV radiation damages the DNA in skin cells.
2. Repeated damage can lead to skin cancer.
3. Hence, the correct option is a).

Teacher's Note:
a) Ozone layer depletion increases the UV radiation reaching the earth.
b) Sunscreen and shade reduce exposure.

16. World Environment day is celebrated on
a) July 1
b) July 5
c) June 1
d) June 5

Answer: d) June 5

1. World Environment Day is observed every year on 5 June.
2. Hence, the correct option is d).

Teacher's Note:
a) The United Nations Environment Programme coordinates the day.
b) Do not confuse it with World Ozone Day, which falls on 16 September.

17. Which one of the following is a non- biodegradable substance
a) DDT
b) Manure
c) paper
d) Cotton cloth

Answer: a) DDT

1. Manure, paper and cotton cloth are decomposed by microorganisms.
2. DDT is a synthetic pesticide that is not broken down by microorganisms.
3. Hence, the correct option is a).

Teacher's Note:
a) DDT accumulates in fat and moves up the food chain.
b) Paper and cotton are biodegradable natural materials.

18. In a terrestrial ecosystem the biomass of ____________ should be the most
a) Herbivore
b) Carnivore
c) Producer
d) Any one of the above

Answer: c) Producer

1. Only about 10% of biomass passes to each higher trophic level.
2. So the first trophic level, the producers, has the largest biomass.
3. Hence, the correct option is c).

Teacher's Note:
a) Biomass decreases at each step, which gives an upright pyramid.
b) Carnivores have the smallest biomass in a terrestrial ecosystem.

19. Identify the proper food chain
a) Grass ----- frog ---- insect ----- snake
b) Grass---- insect ----- frog ------ snake
c) Insect --- frog ---- grass ---- snake
d) Grass --- frog ---- snake ----- insect

Answer: b) Grass---- insect ----- frog ------ snake

1. A food chain starts with a producer, which is grass.
2. Grass is eaten by insects, insects are eaten by frogs and frogs are eaten by snakes.
3. Hence, the correct option is b).

Teacher's Note:
a) Arrows in food chains point from the food to the eater.
b) Options (a) and (d) place a consumer before its food source.

20. Food web is
a) Food served through websites
b) Display of different food items
c) Interlinked food chains
d) Using food items for a fashion dress

Answer: c) Interlinked food chains

1. Most organisms eat more than one kind of food.
2. Many food chains that are connected together form a food web.
3. Hence, the correct option is c).

Teacher's Note:
a) A food web is more stable than a single food chain.
b) If one species is removed, other species can still find food.

21. The best way to dispose waste is by
a) Making a paste of all domestic waste and putting them in a river
b) Separating biodegradable and nonbiodegradable waste before disposing in bins
c) Throw the waste on road side
d) Dumping all domestic waste in litter bin

Answer: b) Separating biodegradable and nonbiodegradable waste before disposing in bins

1. Segregated waste can be composted or recycled easily.
2. Options (a), (c) and (d) pollute water, roads or landfills.
3. Hence, the correct option is b).

Teacher's Note:
a) Segregation at home makes recycling practical.
b) Mixed waste in a bin is hard to process.
c) Biodegradable waste can be turned into compost.

22. Which of the following organism is likely to have maximum concentration of DDT : Algae, fish, water flea, frog, bird

Answer: Bird

1. DDT is stored in fat and passes up the food chain.
2. Birds are at the top of this food chain, so they accumulate the highest concentration.
3. Hence, the organism is bird.

Teacher's Note:
a) Algae have the lowest DDT concentration because they are at the base of the chain.
b) This is biomagnification at work.

23. What is the role of bacteria and fungi in an ecosystem?

Answer:
1. Bacteria and fungi are decomposers.
2. They break down dead plants, dead animals and waste into simple inorganic substances.
3. These substances return to the soil and are used again by plants, so nutrients are recycled.

Teacher's Note:
a) Without them, dead matter would pile up everywhere.
b) Nutrient recycling keeps the soil fertile.
c) Many bacteria and fungi also help in making bread, curd and antibiotics.

24. What are trophic levels?

Answer:
1. Trophic levels are the feeding positions in a food chain.
2. Each level is made of organisms that get their food in the same number of steps from the producers.
3. Producers form the first level, herbivores the second, carnivores the third and so on.

Teacher's Note:
a) Trophic comes from a Greek word meaning nourishment.
b) An organism can belong to more than one trophic level in a food web.

25. How much energy is transferred to the next trophic level in a food chain?

Answer: Only about 10% of the energy is transferred to the next trophic level.

Teacher's Note:
a) This is called the 10% law of energy transfer.
b) The remaining 90% is lost as heat and used up in life processes.

26. Which trophic level has the highest concentration of toxic substances in a food chain?

Answer: The highest trophic level, that is the top carnivores, has the highest concentration of toxic substances.

Teacher's Note:
a) Toxins such as DDT build up in fat and are not excreted.
b) Top carnivores eat many contaminated prey, so the toxin adds up in their bodies.

27. Mention some sources of CFC‘s.

Answer:
1. Refrigerators and air conditioners (as refrigerants).
2. Aerosol sprays such as deodorants and hair sprays (as propellants).
3. Foam blown in packaging materials and fire extinguishers.

Teacher's Note:
a) Many countries have now phased out CFCs under the Montreal Protocol.
b) CFCs are stable, so they reach the upper atmosphere intact.

28. Distinguish between a food chain & a food web

Answer:

Teacher's Note:
a) Food chains are simple models; real ecosystems have food webs.
b) A food web shows how many species depend on each other.
c) Food webs help the ecosystem resist changes in population.

29. What would happen if there are no decomposers on earth?

Answer:
1. Dead plants, dead animals and waste would not decay.
2. Nutrients would remain locked in dead matter and would not return to the soil.
3. Plants would soon lack nutrients, food chains would break down and the earth would be covered with dead matter.

Teacher's Note:
a) Decomposers are essential for the nitrogen and carbon cycles.
b) The whole ecosystem would collapse within a short time.

30. What is a food chain? Write a five step food chain found in grass land with frog as one of the members. What will happen to organisms at different trophic levels if all the frogs are removed?

Answer:
1. A food chain is a sequence of organisms in which each organism is eaten by the next one, and energy passes along the chain.
2. Five step grassland food chain: Grass ---> Grasshopper ---> Frog ---> Snake ---> Hawk.
3. If all frogs are removed, the grasshoppers increase in number because their predators are gone.
4. The increased grasshoppers eat more grass, so the grass decreases.
5. Snakes lose a food source and decrease in number, and hawks that depend on snakes also decrease.

Teacher's Note:
a) Every step in a food chain is a trophic level.
b) Removing one species affects all organisms linked to it.
c) Grass is the producer, so its decline would eventually reduce the whole chain.

31. The number of malaria patients increased tremendously when a large number of frogs were exported from the village .What could be the cause for it? Explain with the help of a food chain.

Answer:
1. Frogs feed on mosquitoes, which spread the malaria parasite.
2. Food chain: Plants ---> Mosquito ---> Frog ---> Snake.
3. When frogs were exported, the mosquitoes were no longer controlled by their predator.
4. The mosquito population grew rapidly, so more people were bitten and infected with malaria.

Teacher's Note:
a) Frogs act as natural controllers of insect pests.
b) Removing a predator can cause a sudden rise in the population of its prey.

32. What are the problems caused by the non-biodegradable wastes that we generate?

Answer:
1. They do not decompose, so they pile up in landfills, drains and water bodies.
2. They block drains and create breeding grounds for mosquitoes and rats.
3. Animals may swallow plastic and die, and toxic chemicals from these wastes pollute soil and water.

Teacher's Note:
a) Plastic bags are a common cause of animal deaths.
b) Toxic chemicals can enter the food chain.
c) Reducing and recycling plastic lowers these problems.

33. Food chains generally consist of only 3 or 4 trophic levels. Why is it so?

Answer:
1. Only about 10% of energy is transferred from one trophic level to the next.
2. At each higher level, the available energy becomes very small.
3. After three or four levels, there is not enough energy left to support another level of organisms.

Teacher's Note:
a) The energy lost as heat limits the length of a food chain.
b) Top predators need a large area of food to meet their energy needs.

34. Observe the food chain Plant (1000 kJ) ---> Goat ---> Lion (a) If autographs occupying the first trophic level are called producers what are herbivores Called as? (b) How much energy does the lion get in the above food chain?

Answer:
(a) Herbivores are called primary consumers.
(b) 1. Plant has 1000 kJ of energy.
2. Goat gets 10% of 1000 kJ = 100 kJ.
3. Lion gets 10% of 100 kJ = 10 kJ.
4. Hence, the lion gets 10 kJ of energy.

Teacher's Note:
a) The word "autographs" in the question is a printing error for "autotrophs", which means producers that make their own food.
b) Plants are producers, goats are primary consumers and lions are secondary consumers.
c) Each step passes on only one tenth of the energy from the step before.

35. Vegetarian or non vegetarian food habit help us in getting more energy. Why?

Answer:
1. A vegetarian food habit gives food directly from producers, which are at the first trophic level.
2. A non-vegetarian food habit takes food from animals that are at higher trophic levels.
3. Energy is lost at each step, so food from lower trophic levels gives more energy to us.
4. Hence, a vegetarian food habit helps us to get more energy.

Teacher's Note:
a) Each trophic step loses about 90% of its energy.
b) Eating plants directly skips the energy losses of the middle steps.
c) This does not mean that non-vegetarian food is unhealthy.

36. How is ozone formed in the upper atmosphere? Why is the damage of ozone layer a cause of concern to us? State cause of this damage.

Answer:
1. Ultraviolet radiation from the sun splits oxygen molecules (O₂) into oxygen atoms.
2. Each oxygen atom combines with an oxygen molecule to form ozone (O₃).
3. The ozone layer absorbs harmful ultraviolet radiation, so damage to it increases UV radiation on the earth.
4. Increased UV radiation causes skin cancer, cataract and harm to crops and aquatic life.
5. The main cause of the damage is chlorofluorocarbons (CFCs) released from refrigerators, air conditioners and aerosol sprays.

Teacher's Note:
a) The ozone layer is in the stratosphere, about 15 to 35 km above the earth.
b) Ozone is harmful at ground level, but it is protective in the upper atmosphere.
c) CFCs release chlorine atoms that break ozone molecules repeatedly.
d) Using ozone-friendly refrigerants reduces the damage.

37. What is environment?

Answer: Environment is the sum of all living and non-living things that surround an organism, including air, water, soil, light, plants and animals.

Teacher's Note:
a) Living things form the biotic part of the environment.
b) Air, water and soil form the abiotic part.

38. What happens when we add our waste to the environment or throw?

Answer:
1. Biodegradable waste is broken down by decomposers, but large amounts create bad smell and attract flies.
2. Non-biodegradable waste stays in the environment for a long time and pollutes soil and water.
3. Waste materials can harm animals and plants and disturb the balance of the ecosystem.

Teacher's Note:
a) Dumping waste in water bodies kills aquatic life.
b) Improper waste also spreads diseases.

39. What are the different types of waste materials?

Answer:
1. Biodegradable waste, which can be broken down by decomposers, such as vegetable peels, leaves and paper.
2. Non-biodegradable waste, which cannot be broken down easily, such as plastics, glass and metals.

Teacher's Note:
a) Some wastes such as used batteries are hazardous and need special disposal.
b) Sorting waste at home makes recycling much easier.

40. What happens after we throw waste away them away?

Answer:
1. Waste is collected and taken to dumping grounds or landfills.
2. Biodegradable waste decomposes slowly and releases gases, while non-biodegradable waste stays for many years.
3. Harmful substances from the waste seep into the soil and groundwater.

Teacher's Note:
a) Landfill gases such as methane add to global warming.
b) Recycling and composting reduce the amount of waste sent to landfills.

41. Why are some substances biodegradable and some non-biodegradable?

Answer:
1. Biodegradable substances are made of natural compounds that decomposers can break down into simple substances.
2. Non-biodegradable substances, such as plastics and DDT, are synthetic compounds with complex structures.
3. Microorganisms do not have the enzymes needed to break these synthetic compounds down.

Teacher's Note:
a) Natural materials are usually made of substances the microbes can use as food.
b) Synthetic materials were developed recently, so microbes have not adapted to them.

42. What are the harmful effects of biodegradable substance?

Answer:
1. When large amounts pile up, they decompose and produce a foul smell.
2. The decay attracts flies, mosquitoes and rats, which spread diseases.
3. Decomposition of large amounts in the absence of air produces methane, a greenhouse gas.

Teacher's Note:
a) Biodegradable waste is harmful only when it is not managed well.
b) Composting in an open pit can cause the same problems.

43. What are the harmful effects of non- biodegradable substance?

Answer:
1. They remain in the environment for a very long time and fill up landfills.
2. They block drains and cause flooding.
3. Animals may eat them and die, and toxic chemicals in them enter the food chain.

Teacher's Note:
a) Plastic in oceans harms marine life.
b) Some non-biodegradable substances, like DDT, accumulate through biomagnification.

44. Name some of the biodegradable plastics.

Answer:
1. Polyhydroxybutyrate (PHB).
2. Polylactic acid (PLA).
3. Polyhydroxyalkanoates (PHA).

Teacher's Note:
a) These plastics are made from plant or microbial sources.
b) They break down faster than ordinary polythene.

45. What are the differences between biodegradable and non-biodegradable wastes. What is Ecosystem? What are the different types of Ecosystem?

Answer:

Difference between Biodegradable and Non-biodegradable Wastes

Ecosystem
An ecosystem is a community of living organisms together with their non-living surroundings that interact with each other.

Types of Ecosystem
1. Natural ecosystems, such as forests, ponds, lakes and oceans.
2. Artificial ecosystems, such as aquariums, gardens and crop fields.

Teacher's Note:
a) Biodegradable and non-biodegradable wastes should be kept separate.
b) Natural ecosystems are self-sustaining, while artificial ones need human care.
c) Ponds and forests are good examples of natural ecosystems.

46. Why does aquarium have to be cleaned once in a while?

Answer:
1. Uneaten food and fish waste decompose and build up in the water.
2. This raises harmful bacteria and ammonia levels and lowers the oxygen content.
3. Regular cleaning keeps the water safe and healthy for the fish.

Teacher's Note:
a) An aquarium is a small, closed ecosystem with limited natural cleaning.
b) Overfeeding is a common cause of dirty water.

47. Do we have to clean ponds or lakes in the same manner of aquarium? Why or why not?

Answer:
1. No, ponds and lakes are large natural ecosystems.
2. Their water is cleaned naturally by decomposers, flowing water, sunlight and dilution.
3. Frequent cleaning would disturb the natural balance, so only excess garbage is removed.

Teacher's Note:
a) An aquarium has a small volume, so waste builds up quickly.
b) Ponds may need removal of weeds or silt when pollution is heavy.

48. What are the different components of echo system?

Answer:
1. Biotic components: producers, consumers and decomposers.
2. Abiotic components: air, water, soil, light, temperature and minerals.

Teacher's Note:
a) The term is ecosystem, not echo system.
b) Producers, consumers and decomposers together make the biotic part of the ecosystem.

49. What are trophic levels? Give an example of a food chain and state the different trophic levels in its.

Answer:
1. Trophic levels are the feeding steps in a food chain.
2. Example food chain: Grass ---> Grasshopper ---> Frog ---> Snake.
3. Grass is the producer at the first trophic level.
4. Grasshopper is the primary consumer at the second trophic level.
5. Frog is the secondary consumer at the third trophic level.
6. Snake is the tertiary consumer at the fourth trophic level.

Teacher's Note:
a) The first trophic level is always producers.
b) Energy decreases at each higher trophic level.
c) Naming levels by position helps in solving food chain questions quickly.

50. What is the role of decomposers in the ecosystem?

Answer:
1. Decomposers break down dead plants, dead animals and waste.
2. They release simple inorganic nutrients into the soil and water.
3. These nutrients are taken up by plants again, so the cycle continues.

Teacher's Note:
a) Bacteria and fungi are the main decomposers.
b) Without decomposers, nutrients would stay locked in dead matter.

51. What are the importances of decomposers?

Answer:
1. They recycle nutrients from dead matter back into the soil.
2. They keep the soil fertile for plant growth.
3. They prevent dead matter from piling up and spreading disease.

Teacher's Note:
a) Decomposition is the link between dead organisms and new life.
b) Compost made by decomposers improves soil structure.

52. What is a food chain?

Answer: A food chain is a sequence in which one organism eats another, and energy and nutrients pass from one organism to the next, for example Grass ---> Rabbit ---> Fox.

Teacher's Note:
a) Arrows show the direction of energy flow.
b) Every food chain starts with a producer.

53. What is food web?

Answer: A food web is a network of many interconnected food chains in an ecosystem, in which many organisms feed on more than one kind of food.

Teacher's Note:
a) Food webs are closer to real feeding relationships than single chains.
b) A food web makes the ecosystem more stable.

54. Define the term ‘biome’.

Answer: A biome is a large naturally occurring community of plants and animals spread over a large area, having a characteristic climate and vegetation, such as a desert, a rainforest or a grassland.

Teacher's Note:
a) Climate decides which biome a region belongs to.
b) Biomes are larger than a single ecosystem.

55. What are the significances of food Chains?

Answer:
1. Food chains transfer energy from producers to consumers.
2. They recycle nutrients through the ecosystem.
3. They keep the population of each organism under control.

Teacher's Note:
a) A predator removes weak or old prey, keeping the prey population healthy.
b) Food chains show how each organism depends on others.

56. How do flows of energy occur in tropic level?

Answer:
1. Producers capture sunlight and convert it into chemical energy in food.
2. Consumers at each trophic level eat the food and use part of its energy for life processes.
3. Only about 10% of the energy is stored in the body and passed on, and the rest is lost as heat.

Teacher's Note:
a) The word "tropic" in the question means "trophic".
b) Energy is lost as heat through respiration at every level.

57. What are the characteristics of energy transfer in the biosphere?

Answer:
1. Energy flow is unidirectional, moving from the sun to producers and then to consumers.
2. Only about 10% of energy passes from one trophic level to the next.
3. The energy lost as heat cannot be reused, so the energy pyramid is always upright.

Teacher's Note:
a) Energy is not recycled, while matter is recycled in the biosphere.
b) Sun is the ultimate source of all energy in the biosphere.

58. Why is energy flow considered as undirectional?

Answer:
1. Energy enters the ecosystem from the sun and moves in only one direction through the food chain.
2. At each trophic level, energy is lost as heat and cannot return to the previous level.
3. Heat energy finally escapes into the atmosphere and cannot be used again by the ecosystem.

Teacher's Note:
a) Matter is recycled, but energy is not.
b) Plants cannot use heat released by animals.

59. What is biomass?

Answer: Biomass is the total mass of living organisms, usually expressed as dry weight, present in a given area or at a particular trophic level.

Teacher's Note:
a) Biomass decreases at each higher trophic level.
b) Dry weight gives a more accurate measure because water content varies.

60. Define biomagnifications.

Answer: Biomagnification is the increase in the concentration of non-biodegradable toxic substances, such as DDT, at each higher trophic level of a food chain.

Teacher's Note:
a) The toxin is stored in fat and is not excreted quickly.
b) The highest concentration is found in top carnivores.

61. How does a food web an important factor of our environment? Describe its four benefits.

Answer:
1. Stability: a food web keeps the ecosystem balanced, because if one species declines, others can still find food.
2. Population control: predators keep the populations of prey species in check.
3. Alternative food sources: consumers can switch to other food when one food source is scarce.
4. Nutrient recycling: decomposers in the web return nutrients to the soil, which supports producers.

Teacher's Note:
a) A food web is a model of how species are connected in nature.
b) Disturbing one part of the web can affect many other species.
c) Diverse food webs are more resistant to disease and climate change.
d) Protecting one species often protects many others.

62. What is 10% Law?

Answer: The 10% law states that only about 10% of the energy stored in one trophic level is transferred to the next trophic level, and the remaining 90% is lost mainly as heat.

Teacher's Note:
a) The law was proposed by Raymond Lindeman.
b) Energy is used in respiration, movement and excretion.

63. How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 1,000 J of energy is available to wheat plants from the sun?

Answer:
1. Food chain: Paddy ---> Mice ---> Snake ---> Hawk.
2. Paddy (producer) receives 1,000 J.
3. Mice receive 10% of 1,000 J = 100 J.
4. Snake receives 10% of 100 J = 10 J.
5. Hawk receives 10% of 10 J = 1 J.
6. Hence, 1 J of energy is available to hawks.

Teacher's Note:
a) The question names wheat plants, but the chain uses paddy as the producer; both are producers with the same energy calculation.
b) Each step uses 10% of the energy of the step before.
c) Only 1 J reaches the hawk from the 1,000 J captured by the producer.

64. Differentiate between food chain and food web?

Answer:

Teacher's Note:
a) A food web contains many food chains that share organisms.
b) Real ecosystems are better described by food webs.

65. Why is damage to the ozone layer a cause of concern? What steps are being taken to limit this damage?

Answer:
1. The ozone layer absorbs harmful ultraviolet radiation from the sun, so its damage lets more UV radiation reach the earth.
2. Increased UV radiation causes skin cancer, eye problems and damage to crops and aquatic life.
3. The Montreal Protocol of 1987 was signed to phase out ozone-depleting substances such as CFCs.
4. Ozone-friendly substitutes are now used in refrigerators and air conditioners.

Teacher's Note:
a) The protocol has helped the ozone layer begin to recover.
b) Individuals can help by avoiding products that release CFCs.
c) UV exposure harms animals, plants and humans alike.

66. Which compounds are responsible for the depletion of ozone layer?

Answer:
1. Chlorofluorocarbons (CFCs).
2. Halons, which are used in fire extinguishers.
3. Other chlorine and bromine containing compounds.

Teacher's Note:
a) CFCs are the main cause of ozone depletion.
b) Nitrogen oxides from high-flying aircraft can also damage ozone.

67. Which disease is caused in human being due to depletion of ozone layer in the atmosphere?

Answer: Skin cancer is caused in human beings, along with cataract and weakened immunity, due to increased UV radiation.

Teacher's Note:
a) UV radiation damages the DNA of skin cells.
b) Wearing sunscreen, hats and sunglasses reduces the risk.

68. Why is ozone layer getting depleted at higher levels of the atmosphere?

Answer:
1. CFCs are stable, so they rise slowly to the stratosphere, the upper layer of the atmosphere.
2. In the stratosphere, UV radiation breaks CFCs and releases chlorine atoms.
3. Each chlorine atom destroys many ozone molecules, so the ozone layer gets depleted there.

Teacher's Note:
a) Ozone is produced and destroyed continuously in the stratosphere.
b) Cold polar clouds make the ozone loss over the poles worse.
c) The effect is strongest at higher altitudes where UV radiation is intense.

69. How is ozone formed in the upper atmosphere? Which compounds are responsible for the depletion of ozone layer?

Answer:
1. Ultraviolet radiation splits oxygen molecules (O₂) into oxygen atoms.
2. Each oxygen atom combines with an oxygen molecule to form ozone (O₃).
3. The compounds responsible for depletion are chlorofluorocarbons (CFCs) and halons.

Teacher's Note:
a) Ozone formation and breakdown happen together in a natural balance.
b) CFCs and halons release chlorine and bromine that destroy ozone.

70. When is World Ozone Layer Preservation Day celebrated?

Answer: World Ozone Day is celebrated on 16 September every year.

Teacher's Note:
a) The day marks the signing of the Montreal Protocol in 1987.
b) It is different from World Environment Day, which is on 5 June.

71. What is green house effect?

Answer:
1. Greenhouse gases such as carbon dioxide, methane and water vapour trap some of the heat radiated from the earth.
2. This trapped heat keeps the earth warm enough for life.
3. An excess of these gases traps too much heat and causes global warming.

Teacher's Note:
a) The natural greenhouse effect is necessary for life on earth.
b) Burning fossil fuels increases carbon dioxide in the air.

72. Suggest activities in our daily life which are eco friendly.

Answer:
1. Carry cloth bags instead of plastic bags when shopping.
2. Segregate waste into biodegradable and non-biodegradable bins.
3. Save water and switch off lights and fans when not in use.
4. Use public transport, cycling or walking for short trips.

Teacher's Note:
a) Small daily habits add up to a large environmental benefit.
b) Planting trees and composting kitchen waste are also eco friendly.

73. How can you help in reducing the problem of waste disposal? Give any two methods.

Answer:
1. Segregation: separate biodegradable and non-biodegradable waste at home before disposal.
2. Composting: convert biodegradable kitchen waste such as vegetable peels into manure.

Teacher's Note:
a) Reduce and reuse also cut the amount of waste produced.
b) Compost improves soil fertility and avoids landfill use.

74. What is the importance of phytoplankton?

Answer:
1. Phytoplankton are microscopic aquatic producers that make food by photosynthesis.
2. They release a large part of the oxygen in the atmosphere.
3. They form the base of aquatic food chains and feed fish and other animals.

Teacher's Note:
a) Phytoplankton also take up carbon dioxide from water and air.
b) Their decline would affect the whole ocean food web.

75. Which pollutants are contributed by airplanes?

Answer:
1. Oxides of nitrogen.
2. Carbon monoxide and carbon dioxide.
3. Unburnt hydrocarbons and soot particles.

Teacher's Note:
a) Nitrogen oxides from aircraft can damage the ozone layer at high altitudes.
b) Soot and particles affect the air quality near airports.

76. How is ozone layer formed in the atmosphere? What is the function of this layer?

Answer:
1. Ultraviolet radiation splits oxygen molecules into oxygen atoms in the stratosphere.
2. These atoms combine with oxygen molecules to form ozone (O₃).
3. The ozone layer absorbs most of the harmful ultraviolet radiation from the sun and protects living organisms.

Teacher's Note:
a) Ozone at ground level is a pollutant, but in the upper atmosphere it protects life.
b) Without this layer, life on earth would be greatly harmed by UV radiation.

77. Name any two biodegradable wastes.

Answer: Vegetable peels and leaves.

Teacher's Note:
a) Paper and cotton are also biodegradable.
b) Such waste can be turned into compost.

78. Name any two non-biodegradable wastes.

Answer: Plastic bags and glass bottles.

Teacher's Note:
a) Metals such as aluminium cans are also non-biodegradable.
b) These should be recycled.

79. Name two aquatic ecosystems.

Answer: Pond and lake.

Teacher's Note:
a) Oceans and rivers are also aquatic ecosystems.
b) Aquatic ecosystems are found in water bodies.

80. Name two terrestial ecosystems.

Answer: Forest and grassland.

Teacher's Note:
a) Deserts are also terrestrial ecosystems.
b) Terrestrial ecosystems are found on land.

81. Give two examples of Artificial ecosystems.

Answer: Aquarium and crop field.

Teacher's Note:
a) Gardens and dams are also artificial ecosystems.
b) Humans design and maintain artificial ecosystems.

82. Which is the ultimate source of the energy for an ecosystem?

Answer: The sun is the ultimate source of energy for an ecosystem.

Teacher's Note:
a) Producers capture solar energy during photosynthesis.
b) Without sunlight, food chains would stop.

83. Name the category of organism which feed the energy into the ecosystems.

Answer: Producers, which are the green plants and blue green algae, bring energy into the ecosystem.

Teacher's Note:
a) Producers are the entry point of energy into the food chain.
b) Consumers and decomposers only use the energy that producers capture.

84. Give the scientific term for organisms which feed directly on plants.

Answer: Herbivores, also called primary consumers.

Teacher's Note:
a) Cow, deer and goat are examples of herbivores.
b) Herbivores occupy the second trophic level.

85. How much of organic matter is available at each trophic level to reach the next level?

Answer: Only about 10% of the organic matter available at a trophic level is passed on to the next level.

Teacher's Note:
a) This is the same as the 10% law.
b) The rest is used in respiration, growth and excretion, or is lost as heat.

86. Name the type of organisms that occupy (i) the first trophic level and (ii) the second trophic level.

Answer:
(i) Producers, such as green plants.
(ii) Primary consumers, that is herbivores.

Teacher's Note:
a) Producers make their own food by photosynthesis.
b) Herbivores feed directly on producers.

87. Define Biomagnification.

Answer: Biomagnification is the increasing concentration of non-biodegradable toxic substances at each successive trophic level of a food chain.

Teacher's Note:
a) DDT and mercury are classic examples.
b) Top carnivores are most affected.

88. Expand UNEP.

Answer: United Nations Environment Programme.

Teacher's Note:
a) UNEP was established in 1972.
b) It coordinates global environmental action.

89. Name the chemical mainly responsible for the damage of ozone layer.

Answer: Chlorofluorocarbons (CFCs).

Teacher's Note:
a) CFCs release chlorine atoms that destroy ozone.
b) One chlorine atom can destroy thousands of ozone molecules.

90. Where are CFCs used?

Answer:
1. In refrigerators and air conditioners as coolants.
2. In aerosol sprays as propellants.
3. In making foam for packaging and in fire extinguishers.

Teacher's Note:
a) Ozone-friendly substitutes are now used in many products.
b) Old refrigerators should be disposed of through authorised recyclers.

Question. Largest Ecosystem of the world are
(A) Forest
(B) Grassland
(C) Great lakes
(D) Oceans
Answer : D

Question. Which of the following belongs to the category of primary consumers?
(a) Eagle and snake
(b) Grasshopper and cattle
(c) Snake and frog
(d) Water beetle and fish
Answer. B

Question. Which of the fallowing groups constitutes a correct food chain ?
(A) Grass → Rabbit → Snake → Eagle
(B) Grass → Goat → Fox → Lion
(C) Goat → Grass → Elephant → Snake
(D) Grass → Wheat → Frog → Goat
Answer : A

Question. Who proposed the term Ecosystem ?
(A) A.G. Tensley
(B) E.P. Odum
(C) Karl Mobius
(D) Earnest Haeckel
Answer : A

Question. Which component is formed by plants in the ecosystem ?
(A) Decomposer
(B) Consumer
(C) Producer
(D) All of above
Answer : C

Question. Which of the following is a biotic components of an ecosystem ?
(A) Living organisms
(B) Temperature
(C) Soil and minerals
(D) All of the above
Answer : A

Question. Which is responsible for increase in global temperature ?
(A) Ozone layer depletion
(B) Acid rain
(C) Green house effect
(D) Lightning
Answer : C

Question. Food web helps in
(a) providing alternative pathways of food availability
(b) checking the overpopulation
(c) ecosystem stability
(d) all of these.
Answer. D

Question.Green house gas produced by incomplete decomposition by anaerobic methanogens is
(a) CH₄
(b) CFCs
(c) CO₂
(d) N₂O
Answer. C

Question. Of the total amount of energy that passes from one trophic level to another in a food chain, about 10% is
(a) transpired
(b) burnt in respiration
(c) stored in body tissues
(d) lost as heat.
Answer. A

Question. Which of the following is true with respect to concept of Biodiversity ?
(a) Biodiversity refers to different species of floara & fauna present in an area
(b) Biodiversity refers to only the flora of given area.
(c) Biodiversity is greater in forests.
(d) Biodiversity is total no. of individuals of a species in given area.
(A) (a) & (b)
(B) (b) & (c)
(C) (a) & (c)
(D) (b) & (c)
Answer : C

(A) T₂
(B) T₃
(C) T₁
(D) T₄
Answer : C

Question. 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

Question. DDT is non-biodegradable chemical when it enters food chain it gets accumulated in each tropical level. This phenomenon is called as?
(A) Eutrophication
(B) Chemical Amplification
(C) Bio magnification
(D) Chemical Magnification
Answer : C

Question. Presence of ………………. is an indicator of pollution level in water
(A) Colour
(B) Coliform bacteria
(C) Rhizo bacteria
(D) Spiral bacteria
Answer : B

Question. The following diagram shows a simple version of energy flow through food web What happens to energy having the decomposers ?

(A) It is used by the decomposers it self
(B) It is reflected from the surface of earth
(C) It is lost as heat
(D) It is used in natural Biocomposting
Answer : D

Question. In a grazing food chain, primary consumers (herbivores) represent
(a) T₁ level
(b) T₂ level
(c) T₃ level
(d) T₄ level.
Answer. B

Question. Which of the following does not help in protecting our environment?
(a) Crop rotation
(b) Treatment of sewage
(c) Deforestation
(d) Judicious use of fertilisers
Answer. C

Question. Now-a-days, which type of cups are being generally used in trains for serving tea/coffee/ soup etc. on daily basis?
(a) Washable glass cups
(b) Washable plastic cups
(c) Disposable paper cups
(d) Disposable cups made of plastic
Answer. C

Question. Shorter food chains provide
(a) more energy
(b) less energy
(c) same energy
(d) any of these.
Answer. A

Question. Maximum number of trophic levels supported in any ecosystem is?
(A) One
(B) Two
(C) Three
(D) Four
Answer : D

Question. Which group of organisms together do not constitute a food chain?
I . Grass, lion, rabbit, wolf
II. Plankton, man, hawk
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

Question. Fish that feeds on zooplanktons is a
(a) primary consumer
(b) secondary consumer
(c) tertiary consumer
(d) decomposer.
Answer. B

Question. If there was no CO₂ in the atmosphere, the earth’s temperature would be
(a) less than the present temperature
(b) same as the present temperature
(c) higher than the present temperature
(d) dependent on O₂ content of air.
Answer. A

Question. As it travels along the food chains, the concentration of DDT
(a) increases
(b) remains constant
(c) decreases
(d) fluctuates randomly.
Answer. A

CBSE Class 10 Science Chapter 15 Our Environment Case Based Questions

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

Grazing food chains are directly dependent upon solar radiations as the primary source of energy. Green plants (or producers) form the first trophic level of the food chain. They synthesise their food by the process of photosynthesis. Herbivores or primary consumers feed upon the producers and form the second trophic level. Herbivores are eaten by carnivores of different categories. These are longer food chains.
Given below are 5 grazing food chains operating in the nature.

Question. Select the option that correctly identifies P,Q and R.
        P                Q                   R
(a) Frog         Deer           Aquatic insect
(b) Frog         Elephant    Phytoplankton
(c) Tadpole    Deer          Zooplankton
(d) Dog         Elephant     Algae
Answer. A

Question. According to the given food chains which of the following animals is both secondary and tertiary consumer?
(a) Rabbit
(b) Tiger
(c) Eagle
(d) Small fish
Answer. B

Question. Top consumer in which of the following food chains will have the maximum energy?
(a) Food chain A
(b) Food chain B
(c) Food chain C
(d) Food chain D
Answer. A

Question. If energy present in producers of food chain D is 20,000 KJ. Then amount of energy present in its secondary consumer will be
(a) 2000 KJ
(b) 20 KJ
(c) 2 KJ
(d) 200 KJ.
Answer. D

Question. What will be the shape of pyramid of biomass of food chain E?

CBSE Class 10 Science Chapter 15 Our Environment Assertion And Reason Based MCQs

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 : There is always an interaction between neighbouring or distant ecosystems.
Reason : An ecosystem is recognised as self - regulating and self - sustaining entity.
Answer. B

Question. Assertion : Pyramid of biomass may be upright or inverted.
Reason : Pyramid showing total biomass produced per unit time is always upright.
Answer. B

Question. Assertion : Man is a social and cultured animal.
Reason : He developed socio-cultural environment and lives in it.
Answer. A

Question. Assertion : Ozone depletion can be reduced by limiting the use of air conditioners and refrigerators.
Reason : Air conditioner and refrigerators release chlorofluorocarbons in the atmosphere that destroy ozone.
Answer. A

Question. Assertion : Paper cups are better option than plastic cups for serving tea.
Reason : Paper cups are biodegradable and can even be disposed off by burning.
Answer. A

CBSE Class 10 Science Chapter 15 Our Environment Very Short Answer Type Questions

Question. Name the radiations that are absorbed by ozone blanket.
Answer. Ultraviolet (UV) radiations

Question.Give reason why ozone layer in the stratosphere is considered useful?
Answer. Ozone layer in the stratosphere protects the living organisms including man from harmful UV radiations of the sun by absorbing most of them.

Question. Rearrange the given members of food chain in the correct trophic level: frog, grass, snake, insect.
Answer. Grass → Insect → Frog → Snake

Question. Why are green plants called ‘producers’?
Answer. Green plants are called ‘producers’ because they prepare their own food in the presence of sunlight and chlorophyll by the process of photosynthesis.

Question. Why are plastics non-biodegradable substances?
Answer. Plastics are non-biodegradable substance because they cannot be broken down by the action of enzymes, bacteria or decomposers.

CBSE Class 10 Science Chapter 15 Our Environment Short Answer Type Questions

Question. Write two causes of depletion of ozone layer.
Answer. Two causes of depletion of ozone layer are :
(a) Use of CFCs (chlorofluorocarbons) in refrigerators and aerosol sprayers.
(b) Release of pollutant nitrogen monoxide by jets.

Question. Grass → Grasshopper → Frog → Snake → Eagle
In the above food chain, which of the organism will have
(i) maximum available energy?
(ii) minimum available energy?
Answer. (i) Grass will have the maximum available energy.
(ii) Eagle will have the minimum available energy.

Question. Producers always occupy the first trophic level in any food chain. Why?
Answer. Producers or green plants have chlorophyll which can trap the solar energy. The first trophic level in a food chain is a producer, i.e., those organisms which can produce food with the help of sunlight and chlorophyll by a process called photosynthesis.

Question. Why are microorganisms like bacteria and fungi important in the ecosystem?
Answer. Microorganisms like bacteria and fungi are important in the ecosystem because they decompose or break down the dead remains of animals and plants. This release the locked nutrients to be recycled in the ecosystem for reuse as raw materials by the producers.

Question. What is landfilling? How is it beneficial to the environment?
Answer. Landfilling is a method of waste disposal in which solid wastes from urban areas are dumped in low lying areas and compacted by rolling with bulldozers. They are then covered with a layer of soil.
Landfilling is an effective method of solid waste disposal in urban areas and at the same time, it helps in reducing the pollution arising out of the waste.

Question. Why proposal of use of kulhads (disposable cups made of clay) in trains was set aside?
Answer. Sometime back, use of kulhads (disposable cups made of clay) was suggested as an alternative of plastic cups.
However, making of kulhads on such a large scale would have resulted in the loss of top fertile soil. Therefore, this proposal was set aside.

Question. Stability of a biotic community in an ecosystem is inversely proportional to its diversity. Do you agree with this statement?
Answer. No, I do not agree with this statement. Stability of a biotic community is directly proportional to its diversity, number of species and their interactions. Larger the number of species within a community, more stable it will be.

Question. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?
Answer. An aquarium is an artificial or man-made ecosystem and thus, is not self-regulatory whereas, ponds and lakes are natural, self-sustaining and complete ecosystems. Therefore, ponds and lakes get cleaned by natural processes but an aquarium needs to be cleaned.

Question. What does a trophic level represent in a food chain? State the position of autotrophs and herbivores in a food chain.
Answer. The various steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic levels.
The position of producers (or autotrophs) in a food chain constitute the first trophic level. They fix up sun’s energy and make it available for consumers. The herbivores or primary consumers (which feed upon plants) constitute the second trophic level in a food chain.

CBSE Class 10 Science Chapter 15 Our Environment Very Short Answer Type Questions

Question. Producers always occupy the first trophic level in any food chain. Why?
Answer. Only producers have the ability to trap solar energy and manufacture organic food through the process of photosynthesis.

Question. The flow of energy in the food chain is unidirectional. Why?
Answer. Energy flows from sun to plants (autotroph), plants to animals (consumer).

Question. Give any two ways in which biodegradable substance would affect the environment.
Answer. They keep the environment clean as they are easily decomposed.
They can easily go through the geochemical cycle with the help of decomposers.

Question. Name any two abiotic components of an environment.
Answer. (a) Climatic factors (light, temperature, rainfall)
(b) Edaphic factor (Soil)

Short Answer Type Question

Question. What will happen if we kill all the organisms in one trophic level?
Answer. The organisms in specific trophic level will not be able to get the food
ii-It will cause a disturbance in food chain and therefore ecological imbalance will take place.

Question. Which gas shield the surface of earth from harmful radiation of the sun. why these radiations are supposed to be harmful for us?
Answer. Ozone gas
Harmful radiation of the sun like UV radiation may causes skin cancer, cataract, fall in immunity in infants, decline in photosynthesis rate etc

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

Question. In a certain study conducted on the occurrence of DDT along food chains in an ecosystem, the concentration of DDT in grass was found to be 0-5 ppm. In sheep, it was 2 ppm and in man it was 10 ppm. Name the phenomenon and define?
Answer. Bio-magnification
Bio-magnification is the increase in the level of a toxic substance with each successive rise in the trophic level of a food chain.

Question. How can we help in reducing the problem of waste disposal? List two ways.
Answer. i-Separation of biodegradable and non-biodegradable wastes
ii-Preparation of compost / vermicomposting from biodegradable waste
iii-Recycling of waste

Long Answer Type Questions

Question. Answer the followingsi-
What is ozone? How is it formed in the atmosphere?
ii- How ozone layer is useful
iii- Name the substances responsible for the depletion of ozone layer.
Answer. i- Ozone is triatomic form of oxygen, O3. Ozone is formed in the upper atmosphere by the action of ultraviolet (UV) radiations over oxygen (O2)
ii- It protects us from harmful UV radiation of sun.
iii- The important ozone depleting substances chlorofluorocarbons (CFC), methane, N2O, chlorine.

Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer?
Answer. simple food chain
Plants ———> Deer ———> Lion.
As per 10 % law only 10 % of energy is transferred to next trophic level-
Energy available to deer = 100J x 10 = 1000 J
Energy available to plants = 1000 x 10 = 10,000 J.

Question. “Energy flow in a food chain is unidirectional”. Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Answer. The producers convert solar energy into chemical energy in the form of organic compounds. The primary consumers (herbivores) derive their nutrition from the producers. According to the energy transfer law, only 10% of energy is transferred from one trophic level to the other. So, the energy that is captured by the producers does not revert to the sun and the energy transferred to the herbivores does not come back to the producers. It just keeps on moving to the next trophic level in a unidirectional way. That is why the flow of energy in the food chain is always unidirectional. A large number of pesticides and chemicals are used to protect our crops from pests and diseases. Some of these chemicals are washed down from the soil, while some enter the water bodies. From the soil, they are absorbed by plants along with water and minerals; and from the water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain. As these chemicals cannot decompose, they accumulate progressively at each trophic level. This increase in the concentration of harmful chemicals with each step of the food chain is called biomagnification. As human beings occupy the top level in any food chain, these chemicals get accumulated in our bodies.

Question. Why bacteria and fungi are called decomposers? List any two advantages of decomposers to the environment.
Answer. Decomposers degrade breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
Advantages:
i- Clean environment by decomposing dead bodies of plants/ animals
ii- Replenish nutrients (Inorganic substance) into soil
iii- Helps in Nutrient recycling

Question. Explain the phenomenon of ozone depletion.What are the factors responsible for it? What are its consequences?
Answer. Ozone depletion means the thinning of ozone layer in the atmosphere. Many chemicals mainly chlorofluorocarbons are responsible for ozone depletion. These are widely used as coolants in refrigerators and air conditioners; in fire extinguishers; in aerosol sprayer and as propellants. Once released in the air, these chemicals produce `active chlorine’ (Cl and ClO radicals) in the presence of UV radiations. These radicals, through chain reaction, then destroy the ozone by converting it into oxygen. A single active chlorine can deplete one lakh ozone molecules through chain reaction. Thinning of ozone layer allows ultraviolet (UV) radiations to pass through it which then strike the earth and cause harmful effects on man, animals and plants.
(i) UV radiations increase incidences of skin cancer and herpes.
(ii) UV radiations cause damage to eyes resulting in dimming of eye sight.
(iii) Cause damage to immune system hence, lowering the body’s resistance.
(iv) Harmful UV radiations increase mortality of developing embryo in the mothers, uterus.
(v) These radiations decline the rate of photosynthesis in plants which ultimately increase the CO2 concentration leading to global warming.

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose of the waste produced in our homes.
Answer. (a) Harmful effects of using plastic bags :
(i) These are non-biodegradable substances. They cannot be decomposed and therefore remains as pollutants in nature for many years.
(ii) The plastic bags choke drains and causes waterlogging.
(iii)The pastic release harmful chemicals in soil, water slowly over to years. Jute bags and cloth bags are the alternatives to the polyethene bags.
(b) Practices to dispose off the waste produced in our homes:
(i) Separation of biodegradable and non- biodegradable wastes.
(ii)The biodegradable waste can be converted to manure.
(iii) Non-biodegradable waste should be disposed off at suitable places from where municipal authorities can pick them up and dispose properly and scientifically.
(iv) Reuse the waste