CBSE Class 10 Science Our Environment Assignment Set 09

This second chapter-wise assignment for CBSE Class 10 Science Chapter 13, Our Environment, carries 1, 2, 3 and 5 mark questions with complete step-by-step answers. The questions test ozone formation and its depletion by CFCs, the harmful effects of UV radiation, biodegradable and non-biodegradable wastes, waste reduction methods and the effect of our lifestyle on the environment.

Very Short Answer Questions (1 Mark each)

Question 1. Which of the following are not biodegradable: Wool, glass, silver foil, leather?
Answer:
Glass and silver foil are not biodegradable. Wool and leather come from animals and are decomposed by microbes.
In simple words: Natural animal products rot; glass and metal foil do not.

Teacher's Note:
1. Biodegradable materials are of plant or animal origin.
2. Metals, glass and plastics are non-biodegradable.

Question 2. What is full form of CFC and UNEP?
Answer:
CFC: Chlorofluorocarbon. UNEP: United Nations Environment Programme.
In simple words: CFCs are chemicals and UNEP is a UN agency.

Teacher's Note:
1. Learn both full forms.
2. UNEP got the nations to freeze CFC production at 1986 levels in 1987.

Question 3. Name the radiations that are absorbed by ozone layer?
Answer:
The ozone layer absorbs the harmful ultraviolet (UV) radiations of the Sun.
In simple words: Ozone blocks UV.

Teacher's Note:
1. UV radiation can cause skin cancer.
2. The layer is in the stratosphere.

Question 4. Why is excessive use of CFC a cause of concern?
Answer:
CFCs release chlorine in the stratosphere which destroys ozone and thins the ozone layer, so more UV radiation reaches the Earth and can cause skin cancer and cataract.
In simple words: More CFC means less ozone and more UV.

Teacher's Note:
1. Link CFC to ozone depletion.
2. Name one harmful effect of UV.

Question 5. Name the gases which have replaced CFCs.
Answer:
CFCs are replaced by hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which do much less damage to the ozone layer.
In simple words: HFCs and HCFCs are safer substitutes.

Teacher's Note:
1. Another answer often written is HFC alone.
2. Some books also list PFCs; HFCs and HCFCs are the standard answer.

Question 6. Ozone is deadly poisonous, still it performs an essential function. How?
Answer:
Ozone is poisonous when breathed in near the ground, but in the stratosphere it forms a shield that absorbs the harmful ultraviolet radiation of the Sun and protects living organisms.
In simple words: Poisonous near us, protective high above us.

Teacher's Note:
1. Mention where the layer is.
2. Good ozone is in the stratosphere.

Question 7. Why should bio-degradable and non-biodegradable wastes discarded into separate dust bins?
Answer:
Biodegradable waste can be decomposed or made into compost, whereas non-biodegradable waste must be recycled or specially disposed of. Since the methods are different, the two should be kept separate; it also saves time and energy.
In simple words: Different wastes need different treatment.

Teacher's Note:
1. Green bin: biodegradable; blue bin: non-biodegradable.
2. Segregation at the source is the first step.

Question 8. Name any two items which can be easily recycled but are generally thrown in the dust-bin by us.
Answer:
Bits of waste paper and plastic bottles of water or cold drinks.
In simple words: Paper and plastic bottles can be recycled.

Teacher's Note:
1. Glass bottles and tin cans are other examples.
2. Recycling makes new products from waste.

Short Answer Questions (2 Marks each)

Question 9. What is ozone and how does it affect any ecosystem?
Answer:
Ozone (O₃) is a molecule made of three atoms of oxygen. At the higher levels of the atmosphere it forms the ozone layer, which shields the Earth from the harmful ultraviolet radiation of the Sun.
UV rays damage organisms; they cause skin cancer, cataract and a weak immune system in humans and also harm plants and animals. When the ozone layer thins, more UV reaches the ecosystem.
In simple words: Ozone is a UV shield, and without it ecosystems are harmed.

Teacher's Note:
1. Write the formula O₃.
2. Mention at least one effect on humans.

Question 10. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer:
It will still have an impact. A very large amount of biodegradable waste cannot be decomposed quickly enough, so it accumulates, gives a foul smell and harmful gases, and becomes a breeding ground for flies and mosquitoes that spread diseases.
However, the effect is much less than that of non-biodegradable waste, since the nutrients return to the soil.
In simple words: Even rotting waste harms us if there is too much of it.

Teacher's Note:
1. Do not answer only 'no impact'.
2. Mention one disease-spreading effect.

Question 11. Mention three methods to reduce amount of wastes produced.
Answer:
(1) Recycling of non-biodegradable waste.
(2) Reuse of items, e.g. newspapers can be used for making carry bags and envelopes.
(3) Making compost of biodegradable domestic waste in pits (or using biogas plants in rural areas).
In simple words: Recycle, reuse and compost.

Teacher's Note:
1. Name three separate methods.
2. Reduce is also a method: buy less.

Question 12. List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer.
Answer:
Causes: (i) chlorofluorocarbons (CFCs) used in refrigerators, air conditioners and aerosol sprays; (ii) nitric oxide released by supersonic jets.
Harmful effects: (i) UV radiation reaching the Earth causes skin cancer, cataract and damage to the immune system; (ii) it reduces crop yield and harms aquatic life.
In simple words: CFCs thin the ozone layer and more UV harms health and crops.

Teacher's Note:
1. Two causes and two effects are asked.
2. Avoid mixing greenhouse gases into this answer.

Question 13. Give any two ways in which biodegradable substances would affect the environment.
Answer:
(1) Decomposition of biodegradable wastes by microbes may release foul-smelling gases and pollute the environment.
(2) They may become a breeding ground for mosquitoes, flies and other pests, which increases the chances of disease.
In simple words: Too much rotting waste smells and spreads disease.

Teacher's Note:
1. The waste is harmful when its amount is large.
2. This is an NCERT question.

Question 14. Why are some substances biodegradable and some non-biodegradable?
Answer:
Microbes such as bacteria and fungi (saprophytes) are specific in their action. They break down natural materials such as paper and vegetable peels, which therefore are biodegradable.
They cannot break down man-made materials such as plastics, DDT and glass, which therefore are non-biodegradable.
In simple words: Microbes can digest natural materials, not man-made ones.

Teacher's Note:
1. Give an example of each kind.
2. The reason is the specific action of microbial enzymes.

Short Answer Questions (3 Marks each)

Question 15. (i) What is the height of ozone from the equator? (ii) Name the rays against which ozone layer provides protection. (iii) Name one effect of depletion of ozone layer.
Answer:
(i) The ozone layer lies in the stratosphere at a height of about 20–26 km above the Earth’s surface at the equator.
(ii) It protects against ultraviolet (UV) rays.
(iii) One effect of its depletion is an increase in skin cancer and cataract in humans.
In simple words: The layer is in the stratosphere, shields against UV, and its loss causes disease.

Teacher's Note:
1. One book gives 10–16 km for part (i), which does not agree with other books (about 20–26 km); the 20–26 km value is used here.
2. Part (iii) accepts any one effect.

Teacher's Note:
1. Write the reactions with arrows.
2. UV radiation is needed for the formation of ozone.

Question 17. (a) Improvement in our lifestyle has resulted in greater amount of waste generation. Suggest one change we can incorporate in our lifestyle in order to reduce non-biodegradable waste. (b) The following organisms form a food chain: Insect, Hawk, Grass, Snake, Frog. Which of these will have highest concentration of non-biodegradable chemicals? Name the phenomenon.
Answer:
(a) Use cloth or jute bags instead of plastic bags, and reuse containers such as jars and bottles.
(b) The food chain is Grass → Insect → Frog → Snake → Hawk. The hawk, being at the top, has the highest concentration of non-biodegradable chemicals. The phenomenon is biomagnification.
Note: the hawk is the top carnivore, not a decomposer.
In simple words: Use cloth bags; the hawk collects the most chemicals through biomagnification.

Teacher's Note:
1. Arrange the chain before answering.
2. Non-biodegradable chemicals are not broken down, so they build up.

Long Answer Questions (5 Marks each)

Teacher's Note:
1. Present the differences in a table.
2. Give two habits clearly.

Question 19. What is ozone? How and where is it formed in the atmosphere? Explain how it affects an ecosystem.
Answer:
Ozone (O₃) is a molecule of three oxygen atoms. It is a poisonous gas near the ground but protective in the stratosphere.
Formation: In the upper atmosphere (stratosphere), high-energy UV radiations split some oxygen molecules into free atoms: O₂ → O + O. The atoms combine with oxygen molecules: O + O₂ → O₃.
Effect on an ecosystem: The ozone layer absorbs most of the harmful UV radiation, protecting plants, animals and humans. If it is depleted, UV rays cause skin cancer, cataract and a weak immune system in humans, harm crops and aquatic life, and disturb the ecosystem.
In simple words: UV makes ozone from oxygen, and the ozone layer in return protects life from UV.

Teacher's Note:
1. Write both reactions.
2. The three parts are what, how and where, and the effect.

Question 20. Mention the negative effect of our lifestyle on the environment.
Answer:
(i) A lifestyle with many vehicles and heavy use of fossil fuels increases air pollution.
(ii) Use of refrigerators, air conditioners and aerosols releases CFCs, which deplete the ozone layer.
(iii) Use of disposable and non-biodegradable items such as plastic bags and cups produces large amounts of waste.
(iv) Sewage and industrial waste released into water bodies pollute them.
(v) Excess use of chemicals in agriculture pollutes the soil and water.
In simple words: Our comfortable lifestyle creates more waste and pollution.

Teacher's Note:
1. Give four or five clear points with examples.
2. Link each point to a specific cause.