NCERT Solutions for Class 10 Science Chapter 13 Our Environment

NCERT
SOLUTIONS
CLASS - 10th

aglase .co

Class : 10th
Subject : Science
Chapter : 15
Chapter Name : Our Environment

Q1 What are trophic levels? Give an example of a food chain and state the different
trophic levels in it.

Answer. Trophic Levels : The various steps in a food chain at which the transfer of food
(or energy) takes place are called trophic levels. Example A food chain operating in a
grassland is given below :
Grass -> Insects -> Frog-> Birds

In this food chain
1. Grass represents �rst trophic level.
2 Grasshopper represents second trophic level.
3. Frog represents third trophic level.
4 Eagle represents fourth tropic level.

Page : 260 , Block Name : Questions

Q2 What is the role of decomposers in the ecosystem?

Answer. (i) Decomposers help in decomposing the dead bodies of plants and animals and
hence act as cleansing agents of the environment.
(ii) Decomposers also help in putting back the various elements of which dead plants and
animals are made, back into the soil, air and water for reuse by the producers like crop
plants.
(iii) They help in recycling of the nutrients.
(iv) They decompose dead remains thereby providing space for new life to settle in the
biosphere

Page : 260 , Block Name : Questions

Q1 Why are some substances biodegradable and some non-biodegradable?

Answer. The microorganism like bacteria and other decomposer organisms (called
saprophytes) present In our environment are speci�c in their action. They break down
the materials or products made from natural materials (say, paper) but do not break
down man-made materials such as plastics. So, it is due to the property of decomposer
organisms of being speci�c in their action that some waste materials are biodegradable,
whereas others are non-biodegradable.

Page : 262 , Block Name : Questions

Q2 Give any two ways in which biodegradable substances would affect the environment.

Answer. (i) Biodegradable substances are decomposed by the action of microorganisms
and decomposed materials are recycled through geo-chemical cycle.
(ii) These substances keep the environment clean.

Page : 262 , Block Name : Questions

Q3 Give any two ways in which non-biodegradable substances would affect the
environment.

Answer. (i) They cause air, water and soil pollution.
(ii) They may cause bio-magni�cation in the food chain and end up in humans.

Page : 262 , Block Name : Questions

Q1 What is ozone and how does it affect any ecosystem?

Answer. Ozone (03) is an isotope of oxygen, i.e., it is a molecule formed by three atoms of
oxygen. At the higher levels of the atmosphere, ozone performs an essential function. It
shields the surface of the earth from ultraviolet (UV) radiations from the sun. These
radiations are highly damaging to organisms. Ultraviolet rays can cause skin cancer.

Page : 264 , Block Name : Questions

Q2 How can you help in reducing the problem of waste disposal? Give any two methods.

Answer. (i) Recycling The solid wastes like paper, plastics and metals, etc. are recycled.
(ii) Preparation of Compost: Biodegradable domestic wastes such as left over food, fruit

and vegetable peels and leaves of potted plants, etc. can be converted into compost by
burying in a pit dug into ground.

Page : 264 , Block Name : Questions

Q1 Which of the following groups contain only biodegradable items?
(a) Grass, �owers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass

Answer. (a) Grass, �owers and leather.

Page : 264 , Block Name : Exercise

Q2 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, �sh and goat

Answer. (b) Grass, goat and human.

Q3 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

Answer. (d) All of the above.

Q4 What will happen if we kill all the organisms in one trophic level?

Answer. The food chain would end and ecological balance would be affected. 1. If the
herbivores are killed, then the carnivores would not be able to get food and would die. 2
If carnivores are killed, then the population of herbivores would increase to
unsustainable level. 3. If producers are killed, then the nutrient cycle in that area would

not be completed.

Q5 Will the impact of removing all the organisms in a trophic level be different for
different trophic levels? Can the organisms of any trophic level be removed without
causing any damage to the ecosystem?

Answer. Yes, the impact of removing all the organisms in a trophic level will be different
for different trophic levels. For example, on removing producers; herbivores would not
be able to survive or they would migrate and ecosystem would collapse. If herbivores are
removed, producers would grow unchecked and carnivores would not get food. If
carnivores are removed, herbivores would increase to unsustainable levels and could
destroy the producers. If decomposers are removed, the dead animals would pile up due
to which the environment would become polluted. In addition to this, if dead animals
will not decompose, the recycling of nutrients in the soil will be stopped and its fertility
will be reduced. As a result the green cover of the earth will be lost. Thus to maintain the
balance of the ecosystem the presence of organisms is necessary at each trophic level.

Q6 What are the problems caused by the non-biodegradable wastes that we generate?

Answer. Biological magni�cation : The increase in concentration of harmful chemical
substances like pesticides in the body of living organisms at each trophic level of a food
chain is called biological magni�cation. Yes, levels of bio-magni�cation would increase
as the trophic level increases and would be the highest for topmost trophic level. It
would affect their biological process such as growth, reproduction, etc.

Q7 What are the problems caused by the non-biodegradable wastes that we generate?

Answer. The problems caused by the non-biodegradable wastes are 1. If the quantity of
non-biodegradable matter increases in the nature then bio-magni�cation of poisonous
chemicals in our body increases. 2 If the non-biodegradal waste keeps on increasing
there will not be left any substance for new organisms. 3 The increasing quantity of non-
biodegradable waste will cause imbalance of ecosystem.

Q8 If all the waste we generate is biodegradable, will this have no impact on the
environment?

Answer. If all the waste we generate is biodegradable, it will also have impact on the
environment If it is disposed off properly, the problem of air, water and soil pollution can
be lessened to an extent. There would be less health problems and humans would be
disease-free But if it is not disposed off properly, it will affect the environment adversely.

Q9 Why is damage to the ozone layer a cause for concern? What steps are being taken to
limit this damage?

Answer. The damage to the ozone layer is a cause for concern because if the ozone layer
in the atmosphere disappears completely, then all the extremely harmful ultraviolet
radiations coming from the sun would reach the earth. These ultraviolet radiations
would cause skin cancer and other ailments in men and animals and also damage the
plants. In an attempt to protect the ozone layer, the United Nations Environment
Programme (UNEP) unanimously forged an agreement among its member countries to
freeze CFC production at 1986 levels.