Our environment class 10 NCERT MCQ & SAQ

 

Our environment class 10 NCERT MCQ & SAQ

Our environment class 10 NCERT  solution

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

Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.

Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.

 

2. Give any two ways in which biodegradable substances would affect the environment.

Biodegradable substances affect the environment by:

→ The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.

→ The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.

 

3. Give any two ways in which non-biodegradable substances would affect the environment.

Non-biodegradable substances affect the environment by:

→ They contaminate soil and water resources as they cannot be decomposed by microorganisms.

→ These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.

 

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

The various links or steps in a food chain at which the transfer of food and energy takes place are called trophic levels.

The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.

In the above fig. Grass is the producer which is eaten by the grasshopper known as the primary consumer. Then the grasshopper is eaten by shrew, secondary consumer and lastly shrew eaten up by owl, tertiary consumer.

 

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

Various role played by decomposers in the ecosystem are:

→ They clean the environment.

→ They decompose biodegradable substances into useful substances.

→ They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.

→ They maintain the nutrient pool by returning back the nutrients in the pool.

 

 

1. What is ozone and how does it affect any ecosystem?

Ozone (O3) is a molecule, made up of three atoms of oxygen.

Ozone (O3) forms a layer in the upper atmosphere. It is very essential for life on this planet. It shields the surface of the earth from ultraviolet radiation (UV) coming from the sun as these radiations are very harmful causing skin cancer and cataract in humans. It also does harm to the crops.

 

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

We can help in reducing the problem of waste disposal by these methods:

→ By separating biodegradable substances from non-biodegradable substances.

→ By reducing, reusing and recycling non-biodegradable substances.

1. Which of the following groups contain only biodegradable items?

(a) Grass, flowers and leather

(b) Grass, wood and plastic

(c) Fruit-peels, cake and lime-juice

(d) Cake, wood and grass

► (c) Fruit-peels, cake and lime-juice

(d) Cake, wood and grass

 

2. Which of the following constitute a food-chain?

(a) Grass, wheat and mango

(b) Grass, goat and human

(c) Goat, cow and elephant

(d) Grass, fish and goat

► (b) Grass, goat and human

 

3. Which of the following are environment-friendly practices?

(a) Carrying cloth-bags to put purchases in while shopping

(b) Switching off unnecessary lights and fans

(c) Walking to school instead of getting your mother to drop you on her scooter

(d) All of the above

► (d) All of the above

 

4. What will happen if we kill all the organisms in one trophic level?

If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an Example, In a food chain Grass → Deer → Lion, If we remove all lions then population of deer will increase which will cause overgrazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.

 

5. 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?

Impact of removing all organisms of a trophic level is different for different trophic levels.

For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can't remove any trophic level without causing damage to the ecosystem as one is dependent on the other for their survival. If we remove any one this will create imbalance in the ecosystem.

 

6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Biological magnification is defined as the phenomena of accumulation or increase in the concentration of some toxic substances at each trophic level.

The levels of biomagnification will be different at different trophic levels. For example, in a pond of water, DDT was sprayed and the producers were found to have 0.04 ppm concentration of DDT. Since many types of planktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as one sea gull eats many clams. Hawk, the top carnivore, has the highest concentration of DDT.

 

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

The problems caused by non-biodegradable wastes are:

→ The cause of biomagnification.

→ They increase pollution.

→ They make the environment unclean.

→ They kill useful microorganisms.

 

8. If all the waste we generate is biodegradable, will this have no impact on the environment?

If all the waste generated would be biodegradable this will also create problems. As the numbers of decomposers will be quite low so wastes cannot be broken down into harmless simpler substances at the right time. It will become breeding ground for flies causing spread of diseases. It will also emit a foul smell which makes the lives of people miserable.

 

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

The damage to the ozone layer a cause for concern because:

→ It causes skin darkening, skin cancer, aging, and corneal cataracts in human beings.

→ It can result in the death of many phytoplanktons that lead to increased global warming.

 

To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.

Our environment class 10 NCERT MCQ 

Question : 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

 

Question : 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

 

Question : 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

 

Question : Replacing Plastic cups by paper cups for selling tea on train may be preferred because

a) Paper cups are biodegradable

b) Paper cups are cheaper

c) Paper cups are stronger

d) Paper cups keep things safe

Answer : A

 

Question : World Environment day is celebrated on

a) July 1 b) July 5

c) June 1 d) June 5

Answer : D

 

Question : Which one of the following is a non- biodegradable substance

a) DDT b) Manure

c) paper d) Cotton cloth

Answer : A

 

Question : 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

 

Question : 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

 

Question : 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

 

Question : 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 

1. Which one of the following will undergo fastest bio-degradation?

(a) Mango seed

(b) Wood

(c) Mango peel

(d) Mango pulp

► (d) Mango pulp

 

2. First link in any food chain is usually green plants because

(a) they are widely distributed

(b) they are fixed at one place in the soil

(c) they alone have the capacity to synthesize food using sunlight

(d) there are more herbivores than carnivores

► (c) they alone have the capacity to synthesize food using sunlight

 

3. In an ecosystem, herbivores represent

(a) producers

(b) primary consumers

(c) secondary consumers

(d) decomposers

► (b) primary consumers

 

4. Which of the following is non- biodegradable?

(a) Wool

(b) Nylon

(c) Animal bones

(d) Tea leaves

► (b) Nylon

 

 

 

 

 

 

5. Ozone layer is damaged by-

(a) methane

(b) carbon-dioxide

(c) Sulfur-dioxide

(d) CFCs

► (d) CFCs

 

6. A food chain always starts with

(a) respiration

(b) photosynthesis

(c) decay

(d) nitrogen fixation

► (b) photosynthesis

 

7. A food chain comprising birds, green plants, fish and man.

The concentration of harmful chemical entering the food chain will be maximum in

(a) green plants

(b) man

(c) birds

(d) fish

► (b) man

 

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

(a) water

(b) polluted air

(c) deficient food supply

(d) decrease in energy at higher trophic levels

► (d) decrease in energy at higher trophic levels

 

9. Which of the following is a logical sequence of food chain

(a) producer → consumer → decomposer

(b) producer → decomposer → consumer

(c) consumer → producer → decomposer

(d) decomposer → producer → consumer

► (a) producer → consumer → decomposer

 

10. Excessive exposure to ultraviolet radiation causes

(a) inflammation of liver

(b) cancer of skin

(c) damage to the lungs

(d) jaundice

► (b) cancer of skin

 

11. Which of the following is an autotroph?

(a) Lion

(b) Insect

(c) Tree

(d) Mushroom

► (c) Tree

 

12. Trophic level in an ecosystem represents

(a) oxygen level

(b) water level

(c) energy level

(d) salt level

► (c) energy level

 

13. Which of the following is biodegradable?

(a) Plastic mugs

(b) Leather belts

(c) Silver foil

(d) Iron nails

► (b) Leather belts

 

14. Which of the following is non-biodegradable-

(a) paper

(b) wood

(c) cloth

(d) plastic

► (d) plastic

 

15. In the garden ecosystem, which of the following are producers?

(a) Insects

(b) Snakes

(c) Grasses

(d) Rabbits

► (c) Grasses

 

16. Which of the following is biodegradable?

(a) Aluminum can

(b) Polythene bag

(c) Cowdung

(d) DDT

► (c) Cowdung

 

 

 

 

 

 

17. Which of the following is not a terrestrial ecosystem-

(a) forest

(b) desert

(c) aquarium

(d) grassland

► (c) aquarium

 

18. Which one of the following pairs belong to the category of primary consumers?

(a) Eagle and snake

(b) Grasshoppers & cattle

(c) Snake and frog

(d) Water beetles & fish

► (b) Grasshoppers & cattle

19. What will happen if all the deer are killed in the given food chain?

Grass → Deer → Lion

(a) The population of grass decreases.

(b) The population of lions increases.

(c) The population of lions remains unchanged.

(d) The population of lions decreases and grass increases.

► (d) The population of lions decreases and grass increases.

 

20. The depletion of the ozone layer causes

(a) global warming

(b) earthquakes

(c) increased UV radiations

(d) acid rain

► (c) increased UV radiations

 

21. Which of the following is an abiotic component of an ecosystem?

(a) Humus

(b) Bacteria

(c) Plants

(d) Fungi

► (a) Humus

 

22. Acid rain is caused by the oxides of

(a) carbon

(b) nitrogen only

(c) sulfur only

(d) sulfur and nitrogen

► (d) sulfur and nitrogen

 

23. The decomposers in an ecosystem-

(a) convert organic material to inorganic forms

(b) convert inorganic material to simpler forms

(c) convert inorganic material into organic compound

(d) do not break down organic compound

► (a) convert organic material to inorganic forms

 

24. Which of the two in the following sets belong to the same trophic level?

(a) Grass : Grasshopper

(b) Goat : Spider

(c) Hawk : Rat

(d) Frog : Lizard

► (d) Frog : Lizard

 

25. The second trophic level is always of-

(a) herbivores

(b) autotrophs

(c) carnivores

(c) producers

► (a) herbivores

 

26. The ecosystem of earth is known as-

(a) biome

(b) community

(c) biosphere

(c) association

► (c) biosphere

 

27. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about-

(a) 1%

(b) 8%

(c) 5%

(d) 10%

► (a) 1%

 

28. Flow of energy in an ecosystem is always-

(a) unidirectional

(b) bidirectional

(c) multidirectional

(d) no specific direction.

► (a) unidirectional

 

 

 

 

 

 

 

 

 

29. In natural ecosystems, decomposers include-

(a) only bacteria and fungi

(b) only microscopic animals

(c) herbivores and carnivores

(d) both (b) and (c)

► (a) only bacteria and fungi

 

30. Assertion: Ozone layer is getting depleted at upper atmosphere which is a cause of concern.

Reason: CFC reacts with ozone and breaks it.

(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

(e) Both A and R are false.

► (a) Both A and R are true and R is the correct explanation of A.

 

31. Assertion: Vegetarian food habits are more beneficial to organisms.

Reason: Only 10% energy is available as food from one trophic level to next.

(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

(e) Both A and R are false.

► (a) Both A and R are true and R is the correct explanation of A.

 

32. Assertion: Biodegradable waste and non biodegradable waste should be discarded separately,

Reason: Biodegradable waste is not harmful.

(b) Both A and R are true but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

(e) Both A and R are false.

► (c) A is true but R is false.

Our environment class 10 NCERT  SAQ

. How is the increase in demand for energy affecting our environment adversely?

Answer. The increase in demand for energy affects our environment adversely. Due to this increase, pollutants like CO,C02 , S02, etc., are released into the atmosphere which leads to greenhouse effect.

3. Why is the ozone layer getting depleted at the higher levels of the atmosphere? [Delhi (C)]

Answer. Ozone layer is getting depleted at the higher levels of the atmosphere due to the effect of chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers.

4. Name any two abiotic components of an environment. [Delhi (C)]

Answer. Two abiotic components of an environment are temperature and rainfall.

5. Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment. [Delhi]

Answer. Bacteria and fungi break down the dead remains and waste products of organisms. These microorganisms are called the decomposers as they break down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.

Two advantages of decomposers to the environment are as follows:

1. Decomposers feed on the dead bodies of plants and animals. They return the simple components to soil and help in making the ecosystem steady by recycling nutrients. They, therefore, create a balance in the environment.

2. They also act as scavengers or cleansing agents of the atmosphere.

6. What are the two main components of our environment? [Delhi]

Answer. The two main components of our environment are the biotic or living components and abiotic or non-living components.

7. Why are green plants called ‘producers’? [All India]

Answer. Green plants are called ‘producers’ because they can produce food by photosynthesis in the presence of sunlight.

8. Which disease is caused in human beings due to depletion of the ozone layer in the atmosphere? [Foreign]

Answer. Skin cancer is caused in human beings due to the depletion of ozone layer in the atmosphere.

9. How is ozone formed in the upper atmosphere? Why is the damage of the ozone layer a cause of concern to us? State a cause of this damage. [Delhi(C)]

Answer. Ozone is formed in the upper atmosphere by the reaction of ultraviolet (UV) radiations on oxygen (02) molecules.

The damage to the ozone layer is a cause of concern to us as due to its damage, more ultraviolet rays reach the earth’s surface causing various health hazards.

A cause of this damage is the presence of large amounts of chlorofluorocarbons in the atmosphere.

10. State two problems caused by the non- biodegradable waste that we generate in our daily life. [All India (C)]

Answer. Two problems caused by non-biodegradable waste that we generate in our daily life are:

1. It clogs drains.

2. It causes water and soil pollution.

11. What are biodegradable and non- biodegradable substances? Select two biodegradable pollutants from the following: Agricultural waste, glass, plastic, sewage, DDT. [Ail India (C)]

Answer. Biodegradable substances are those substances which are broken down into simpler, harmless substances in nature in due course of time by the biological processes such as micro organisms like certain bacteria.

Non-biodegradable substances are those substances which cannot be broken down into simpler, harmless substances in nature.

Two biodegradable pollutants are agricultural waste and sewage.

12. Construct an aquatic food chain showing four trophic levels. [All India]

Answer. Food chain in aquatic ecosystem:

13. Explain ‘biological magnification’ with the help of an example. [All India]

Answer. Pesticides used in crops are washed down into the soil. From soil these are absorbed by plants along with water and minerals and thus, they enter the food chain. While consuming the crops, human beings also consume these pesticides which get accumulated in our bodies. This phenomenon is known as biological magnification.

14. Describe how decomposers facilitate recycling of matter in order to maintain balance in the ecosystem. [Foreign]

Answer. Decomposers are micro organisms that obtain energy from the chemical breakdown of dead organisms of animals or plants. These microorganisms breakdown the complex organic substances of dead organisms into simple inorganic substances that go into the soil and are used up once more by the plants. Decomposers thus, help in recycling of matter.

15. Explain the phenomenon of “biological magnification” How does it affect organisms belonging to different trophic levels particularly the tertiary consumers? [Delhi]

Answer. The process in which harmful chemicals enter a food chain and get accumulated progressively at each trophic level is called biological magnification.

Harmful and toxic chemicals enter our bodies when they are added to soil and water. Use of pesticides to protect the food crops from diseases and pests and chemical wastes of factories are dumped in open or disposed off into rivers. These chemicals are washed down into the soil and ultimately to the water table or get absorbed or taken up from the soil by the plants along with water and minerals and in this way harmful chemicals enter the food chain. The quantity of these harmful chemicals increase with increase in trophic level of the food chain because these substances are not degradable. Man is at the top of the food chain, so concentration is maximum in human beings.

Thus, accumulation of DDT has been maximum in man as DDT is used to destroy pests. DDT is accumulated in the following way in this food chain:

This is the reason why our food grains such as wheat and rice, vegetables and fruits and even meat contain varying amounts of pesticides residues. So, the highest trophic level at the extreme right of the food chain has the maximum concentration of harmful chemicals in a food chain.

16. “Damage to the ozone layer is a cause for concern.” Justify this statement. Suggest any two steps to limit this damage. ‘ [Delhi]

Answer. Ozone layer prevents the harmful ultraviolet radiation from entering the atmosphere and reaching the earth’s surface. Depletion of ozone layer has become a cause for concern because it can cause serious effects on human body and other organisms of the environment like fatal diseases such as skin cancer, changes in genetic material DNA, eye damage, etc.

Two steps to limit this damage are as follows:

1. 

   Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.

2.  Control over large scale nuclear explosions and limited use of supersonic planes

7. What will happen if we kill all the organisms in one trophic level? [Delhi]

Answer. If we kill all the organisms in one trophic level, the following effects will take place:

1. The population of organisms in the previous trophic level will increase.

2. The organisms in the next trophic level will not be able to get the food, so they will migrate to some other ecosystem or die.

3. It will cause an ecological imbalance in the food chain.

18. Why did the United Nations act to control the production of chlorofluorocarbons (CFCs) used in refrigerators? [Delhi]

Answer. CFCs deplete the ozone layer around the earth, hence their production is controlled by the United Nations.

19. Which compounds are responsible for the depletion of the ozone layer? [Delhi]

Answer. The compounds responsible for the depletion of ozone layer are chlorofluorocarbons (CFCs).

20. Define ‘trophic level’. [Delhi]

Answer. Trophic level is the position that an organism occupies in a food chain, where transfer of food or energy takes place.

21. What are the various steps in a food chain called? [Delhi]

Answer. The various steps in a food chain are called trophic levels.

22. What is the important function of the presence of ozone in earth’s atmosphere? [Delhi]

Answer. The important function of the presence of ozone in earth’s atmosphere is that it shields the surface of the earth from ultraviolet (UV) radiations of the sun.

23. Give an example to illustrate that indiscriminate use of pesticides may result-in the degradation of the environment. [All India]

Answer. The pesticides used in crop fields are washed down into the water bodies. From water bodies, these are absorbed by aquatic plants and animals of a food chain and thereby degrade the environment.

24. Why is it necessary to conserve our environment? [All India]

Answer. It is necessary to conserve our environment to prevent depletion of natural resources and environmental damage, thereby sustaining life.

25. What is meant by a biodegradable waste? [All India]

Answer. Biodegradable wastes are those substances which are broken down into simpler, harmless substances in nature in due course of time by the biological processes such as action of microorganisms like certain bacteria.

Examples: Urine and fecal matter, sewage, agricultural residue, paper, wood, cloth and cattle dung.

26. What is the role of decomposers in the ecosystem? [Foreign]

Answer. Role of decomposers in the environment:

1. They return the nutrients to the nutrient pool.

2. They help in completing the different biogeochemical cycles, thus they maintain the balance in the ecosystem.

27. What step is being taken to limit the damage to the ozone layer? [Foreign]

Answer.

1. Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.

2. 

   Control over large scale nuclear explosions and limited use of supersonic planes.

28. Why are some substances non- biodegradable? [Foreign]

Answer. Some substances are non-biodegradable because they cannot be broken down into simpler harmless substances in nature.

29. Which class of chemicals is linked to the decrease in the amount of ozone in the upper atmosphere of the earth? [Delhi]

Answer. The chemical compound Chlorofluorocarbon is responsible for the decrease of ozone in the upper atmosphere of the earth.

30. Name two decomposers operating in our ecosystem. [All India 2011; Delhi]

Answer. Bacteria and fungi.

31. Select two non-biodegradable substances from the following waste generated in a kitchen: spoiled food, paper bags, milk bags, vegetable peels, tin cans, used tea leaves. [Delhi]

Answer. Milk bags and tin cans.

32. What happens when higher energy ultraviolet radiations act on the oxygen at the higher level of the atmosphere? [All India]

Answer. When high energy ultraviolet radiations act on oxygen, ozone is produced:

33. In a food chain, 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? [All India ]

Answer. 10 J will be available to the secondary consumer to transfer to the tertiary consumer.

34. Write the name and formula of a molecule made up of three atoms of oxygen. [All India]

Answer. Ozone and its chemical formula is O3.

35. List two man-made ecosystems. [All India]

Answer. Gardens and ponds are man-made ecosystems.

36. Consider the following food chain which occurs in a forest: Grass -> Deer -> Lion

If 10000 J of solar energy is available to the grass, how much energy would be available to the deer to transfer it to the lion? [Foreign]

Answer. 10 J energy would be available to deer to transfer to lions.

37. Which of the following belong to the first trophic level of a food chain? Grass, Grasshopper, Plants, Rat, Tiger [Foreign]

Answer. Grass and plants belong to the 1st trophic level of a food chain.

38. Name the phenomenon in which non-biodegradable chemicals get accumulated progressively at each trophic level of a food chain. [Foreign]

Answer. Biological magnification.

Q1. Name two natural ecosystems.    [CBSE 2016-17 C]

Some natural ecosystems are:

• Temperate forest

• Tropical forest

• Grassland

• Ocean

• Lake

• Types of Natural Ecosystem

 

Q2. What are decomposers? Write the role of decomposers in the environment.    [CBSE 2016-17 C]

Decomposers are microorganisms that derive their nutrition from dead remains and waste products of organisms.

They play a vital role in our environment by breaking down the complex organic substance into simple inorganic substance which is made available for plants and other organisms. Hence they act as scavengers and not only keep the environment clean but also replenish the minerals.

 

Q3. (a) What is an ecosystem? List its two main components.

(b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.    [CBSE 2013,2017]

(a) A self-sustaining functional unit consisting of living and nonliving components is called an ecosystem.

Components: Biotic components like plants and animals. Non-biotic components like soil, wind, light etc.

(b) A pond is a complete, natural and self-sustaining ecosystem whereas an aquarium is an artificial and incomplete ecosystem, without decomposers therefore it needs regular cleaning for proper running.

 

Q4. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day.’    [Delhi 2017]

(a) Why should the ozone layer be protected to save the environment?

(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of the ozone layer as well as the environment.

(a) Ozone layer at the higher levels of the atmosphere, acts as a shield to protect earth from the harmful effects of the ultraviolet (UV) radiations; hence, it should be protected.

(b) 

• Urging the people to not to buy aerosol products with CFC that are available in the market.

• Conducting poster making competition or street plays presenting the importance of the ozone layer on earth.

 

Q5. Your mother always thought that fruit juices are very healthy for everyone. One day she read in the newspaper that some brands of fruit juices in the market have been found to contain certain levels of pesticides in them. She got worried as pesticides are injurious to our health.    (Foreign 2017)

(а) How would you explain to your mother about fruit juices getting contaminated with pesticides?

(b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit cause harm and damage to our organs. Name the phenomenon and write about it.

(a) 

• Pesticides are the chemicals used to protect our crops from diseases and pests.

• These chemicals are washed down either into the soil or into water bodies.

• From the soil, they are absorbed by the terrestrial plants along with water and minerals.

• From the water bodies, they are absorbed by the aquatic plants.

• When the fruits of these plants are used to prepare fruit juices, they are contaminated with the pesticides.

(b)

• The phenomenon is called biomagnification. It is the phenomenon in which certain harmful chemicals enter the food chain and get accumulated and increase in concentration at successive trophic levels.

• It is because they are not degradable.

• The maximum concentration of these chemicals is found in the top level consumers.

 

Q6. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer?    [AI 2017]

Plants → Deer → Lion

1,000,000 J of energy was available to the producer.

 

Q7. Why should biodegradable and non-biodegradable wastes be discarded in two separate dustbins?    [AI 2017(C); Delhi 2013,15]

The biodegradable and non-biodegradable wastes must be discarded in two different dustbins because biodegradable wastes get decomposed by the microorganisms whereas non-biodegradable wastes can be recycled and reused.

 

Q8. Name any two man-made ecosystems.    [Foreign 2017]

Agricultural/crop fields, aquaria, gardens,

 

Q9. We often use the word environment. What does it mean?    [Foreign 2016]

It is the sum total of all external conditions and influences that affect the life and development of an organism, i.e. the environment includes all the physical or abiotic and biological or biotic factors.

 

Q10. Why are green plants called producers?    [Delhi 2016]

Green plants can produce their own food by photosynthesis from inorganic compounds and hence are called producers.

 

Q11. What is ten percent law? Explain with an example how energy flows through different trophic levels.    [Delhi 2015]

Energy available at each successive trophic level of the food chain is ten percent of that at the previous level.

This is called ten percent law. Thus, 90 percent energy is lost to the surroundings at each trophic level. However, plants absorb only one per cent of radiant energy of the Sun during photosynthesis. This is explained as under :

 

Q12. What is ozone? How and where is it formed in the atmosphere? Explain how it affects the ecosystem.    [Foreign 2015]

Ozone is an isotope of oxygen, i.e. it is a molecule formed by 3 atoms of oxygen.

Ozone exists in the ozone layer of the stratosphere. At higher levels o f the atmosphere, the O2 molecule breaks down to 2 oxygen atoms. The oxygen atom then combines with the oxygen molecule to form ozone.

Ozone layer in the atmosphere prevents UV rays from reaching earth. Exposure to excess UV rays causes skin cancer, cataracts and damages the eye and immune system. It also decreases crop yield and reduces population of phytoplankton, zooplankton and certain fish larvae which are an important constituent of aquatic food chain. It also disturbs rainfall, causing ecological disturbance and reduces global food production. Thus, it affects the ecosystem.

 

Q13. “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.    [Foreign 2015]

The energy flow through different steps in the food chain is unidirectional. The energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores, i.e. it moves progressively through various trophic levels. Thus energy flow from sun through producers to omnivores is in a single direction only.

Pesticides are sprayed to kill pests on food plants. The food plants are eaten by herbivores and alongwith the food, pesticides are also eaten by the herbivores. Herbivores are eaten by carnivores and alongwith the herbivore animal, pesticide also enters the body of the carnivore. Man eats both plants and animals and pesticide alongwith food enters the body of humans. Concentration of pesticides increases as we move upward in the food chain and the process is called biomagnification.

 

Q14. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain.    [AI 2015]

Ecosystem: It is the structural and functional unit of the biosphere, comprising all the interacting organisms in an area together with the non-living constituents of the environment. Thus, an ecosystem is a self-sustaining system where energy and matter are exchanged between living and nonliving components.

Main components of ecosystem:

Biotic Component: It means the living organisms of the environment-plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.

Abiotic Component: It means the non-living part of the environment-air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part of the abiotic environment.

An aquarium is an artificial and incomplete ecosystem compared to ponds or lakes which are natural, self-sustaining and complete ecosystems where there is a perfect recycling of materials. An aquarium therefore needs regular cleaning.

 

Q15. Write the full name of the group of compounds mainly responsible for the depletion of the ozone layer.    [Foreign 2015]

CFC → Chlorofluorocarbon

 

Q16. Which of the following are always at the second trophic level of the food chains?

Carnivores, Autotrophs, Herbivores    [AI 2015]

Herbivores are always at the 2nd trophic level.

 

Q17. The following organisms form a food chain. Which of these will have the highest concentration of nonbiodegradable chemicals? Name the phenomenon associated with it.

Insects, Hawk, Grass, Snake, Frog.    [Foreign 2015]

Hawk will have the highest concentration of non-biodegradable chemicals. The phenomenon is called biomagnification.

 

Q18. The first trophic level in a food chain is always a green plant. Why?    [AI 2015]

Only green plants can make their own food from sunlight. Green plants, therefore, always occupy the 1st trophic level in a food chain.

 

Q19. What will be the amount of energy available to the organism of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?    [AI 2015]

100 Joules of energy will be available to the organism of the 2nd trophic level.

 

Our environment class 10 NCERT long question:

 

Q1. (a) How can we help in reducing the problem of waste disposal? Suggest any three methods.    [Delhi 2019]

(b) Distinguish between biodegradable and nonbiodegradable wastes.    [DoE, A1 2011]

(a) The three methods of waste disposal are:

• Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remolded or reprocessed to new materials.

• Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, leftover food, grass clippings, human and animal waste can be converted into compost by burying this waste into ground and can be used as manure.

• Incineration: Burning dawn many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed of in landfill.

(b) Differences between:

Biodegradable wastes	Non-biodegradable wastes
(i) These wastes can be broken-down into non-poisonous substances in nature by the action of microorganisms.	(i) These wastes cannot be broken-down into non-poisonous substances by microorganisms.
(ii) They get recycled thus, they do not need any dumping sites.	(ii) They cannot be recycled thus, they require dumping  sites.

 

Q2. (a) What is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it.    [AI 2015]

(b) With the help of an example, explain that a garden is an ecosystem.

(c) Why only 10% energy is transferred to the next trophic level?

(a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.

(b) A garden comprises different kinds of flora and fauna such as grasses, flowering and nonflowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component consisting of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.

(c) Only 10% energy is transferred to the next trophic level because the other 90 percent is used for things like respiration, digestion, and running away from predators.

Why are some substances biodegradable and some non-biodegradable ? (CBSE A.L 2007)

Answer:

Substances which can be degraded and disposed of naturally by saprophytic organisms or decomposers are called biodegradable, e.g, organic remains, garbage, sewage, livestock waste. Substances which cannot be degraded by saprophytes are known as non-biodegradable. They are mostly man-made articles like pesticides, plastic, polythene, synthetic fibers, etc. Biodegradable articles are formed naturally in the biosphere. Decomposer organisms feed on them by secreting digestive juices and absorbing the solubilised substances. Biogenetic nutrients are released in the process called mineralisation. Non-biodegradable articles pile up in nature because decomposers do not have enzymes to degrade them.

 

 

 

“Damage to the ozone layer is a cause of concern.” Justify the statement. Suggest any two steps to limit this damage. (CBSE Delhi 2008 C)

Answer:

Cause of Concern: Ozone layer present in the stratosphere has thinned out by about 8% over the equator and more so over Antarctica where a big ozone hole appears every year. This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing an increased number of skin cancers, cataracts and reduced immunity in human beings. There is increased incidence of blinding of animals, death of young ones, reduced photosynthesis, higher number of mutations and damage to articles.

Steps to Limit Damage,

1. Ban on production and use of halons.

2. Ban on production and use of chlorofluorocarbons.

Why are bacteria and fungi called decomposers ? List any two advantages of decomposers to the environment.(CCE 2011)

(a) Decomposers: Most of the bacteria and fungi are saprophytes. They obtain their nourishment from organic remains. For this they secrete digestive enzymes over the remains. The remains are converted into soluble absorbable form. This results in decomposition of organic matter. Therefore, bacteria and fungi are called decomposers.

(b) Advantages:

1. Scavengers: Decomposers function as scavengers by removing organic remains and cleansing the earth.

2. Mineralisation: Decomposers release inorganic nutrients trapped in organic remains. The same are recycled.

Energy flow in a food chain is unidirectional”. Justify this statement. Explain how the pesticides enter the food chain and subsequently get into our body. (CCE 2014)

Energy Flow is Unidirectional:

An ecosystem does not have its own source of energy. It receives the same from the sun. Green plants or producers trap the solar energy and change it into chemical form during synthesis of food. Herbivores obtain energy from the food they take. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes to primary carnivores. However, only about 10% of herbivore energy is passed into the body mass of primary carnivores.

The rest is dissipated. From primary carnivores the energy passes into secondary carnivores (10%), etc. It is ultimately lost as heat.

Since energy available decreases at every trophic level, very little of it is available at higher trophic levels. There is dissipation of energy at every step of its transfer and transformation. Hence it cannot flow in the reverse direction i.e., energy flow is unidirectional from sun to plants, plants to animals, animals to animals, organic remains to decomposers and dissipation as heat.

Pesticides: Pesticides are sprayed over crop plants in order to protect them from pests. They not only enter the crop plants but also pass into soil and reach the water table as well as water bodies where they become part of the food chain. With rise of trophic level the/ undergo biomagnification. Human beings obtain pesticides from their food. They accumulate in the human body in toxic amounts as human beings are long-lived and continue to feed on pesticide contaminated foods.

a) What are trophic levels in a food chain ?

(b) Explain the flow of energy through the food chain.

(c) Write a four trophic level food chain and represent it in the form of an ecological pyramid. (CCE 2013)

Answer:

(a) Trophic Levels. They are steps or divisions of the food chain which are characterized by particular methods of obtaining food, e.g., producers (T1), herbivores (T2), primary carnivores (T3), etc.

(b) Flow of Energy Through the Food Chain. Energy enters a food chain through producers. Producers or green plants trap solar energy and convert it into chemical energy of food during photosynthesis. From producers energy passes into herbivores. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes into primary carnivores, again with a lot of dissipation. Only about 10% of herbivore energy is passed into the body mass of primary carnivores. From primary carnivores, nearly 10% energy passes into secondary carnivores and so on. It is ultimately lost as heat.

(c) Aquatic Four Trophic Level Food Chain.

Phytoplankton ———> Zooplankton ———> Small Carnivorous Fish ———> barge Carnivorous Fish.