Class 10 Important Questions and Answers on Our Environment

Q. No. 1) Multiple Choice Questions (MCQs)

i. Which of the following organism convert organic material to inorganic forms?
a. Producers
b. Herbivores
c. Carnivores
d. Decomposers
Ans. Option (d)
ii. If a deer is eaten by a tiger, then the energy transfer will be from
a. Producer to decomposer
b. Producer to primary consumer
c. Primary consumer to secondary consumer
d. Secondary consumer to environment
Ans. Option (c)
iii. In the given food chain, suppose the amount of energy at the fourth trophic level is 5
kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
a. 5 kJ
b. 50 kJ
c. 500 kJ
d. 5000 kJ
Ans. Option (d)
iv. Assertion: The food chain is responsible for the entry of harmful chemicals into our
bodies.
Reason: The length and complexity of food chains vary greatly.
Options
a. Both A and R are true, and R is the correct explanation of the assertion.
b. Both A and R are true, but R is not the correct explanation of the assertion.
c. A is true, but R is false.
d. A is false, but R is true.
Ans. Option (b)
v. Assertion: A greater number of individuals are present in lower trophic levels.
Reason: The flow of energy is unidirectional.
Options
a. Both A and R are true, and R is the correct explanation of the assertion.
b. Both A and R are true, but R is not the correct explanation of the assertion.
c. A is true, but R is false.
d. A is false, but R is true.
Ans. Option (b)
vi. What will happen if deer is missing from the food chain given below?
Grass → Deer → Tiger
a. The population of tigers increases
b. The population of grass decreases
c. Tiger will start eating grass
d. The population of tigers decreases and the population of grass increases
Ans. Option (d)
Q. No. 2) Case-based Questions
I. Read the following and answer the questions.
Food chains are very important for the survival of most species.

i. If 10,000 J solar energy falls on green plants in a terrestrial ecosystem, what

percentage of solar energy will be converted into food energy?
a. 10,000 J
b. 100 J
c. 1000 J
d. It will depend on the type of the terrestrial plant
Ans. Option (b)
ii. If Ravi is consuming curd/yogurt for lunch, which trophic level in a food chain he
should be considered as occupying?
a. First trophic level
b. Second trophic level
c. Third trophic level
d. Fourth trophic level
Ans. Option (c)
iii. The decomposers are not included in the food chain. The correct reason for the same
is because decomposers:
a. Act at every trophic level of the food chain
b. Do not break down organic compounds
c. Convert organic material to inorganic forms
d. Release enzymes outside their body to convert organic material to inorganic forms
Ans. Option (a)
iv. Matter and energy are two fundamental inputs of an ecosystem. Movement of
a. Energy is bidirectional and the matter is repeatedly circulating
b. Energy is repeatedly circulation and the matter is unidirectional
c. Energy is unidirectional and the matter is repeatedly circulating
d. Energy is multidirectional and the matter is bidirectional
Ans. Option (c)
v. Which of the following limits the number of trophic levels in a food chain?
a. Decrease in energy at higher trophic levels
b. Less availability of food
c. Polluted air
d. Water
Ans. Option (a)
II. Read the following and answer the questions.
Observe the food web and answer the questions given below:

i. The mussel can be described as

a. Producers
b. Primary consumer
c. Secondary consumer
d. Decomposer
Ans. Option (c)
ii. Which trophic level is incorrectly defined?
a. Carnivores – Secondary or tertiary consumers
b. Decomposers – microbial heterotrophs
c. Herbivores – primary consumers
d. Omnivores – molds, yeast, and mushrooms
Ans. Option (d)
iii. The given figure best represents:
a. Food chain in forest, pond, and grassland
b. Food chain in grassland, pond, and forest
c. Food chain in forest, grassland, and pond
d. Food chain in pond, forest, and grassland
Ans. Option (c)
iv. Why do all food chains start with plants?
a. Because plants are easily grown
b. Because plants are nutritious
c. Because plants can produce their own energy
d. Because plants do not require energy
Ans. Option (c)
v. In the food web, what two organisms are competing for food?

a. A and B
b. D and F
c. A and C
d. B and D
Ans. Option (d) [B and D are present at the same trophic level. They consume the same
organisms and thus compete for food. C and D are also competing for food but it is not in the
options.]
Q. No. 3) What is an ecosystem?
Ans. Ecosystem: All the interacting organisms in an area together with the non-living
constituents of the environment form an ecosystem. An ecosystem consists of biotic
components comprising living organisms and abiotic components comprising physical factors
like temperature, rainfall, wind, soil, and animals.
Types of Ecosystems:
i. Natural ecosystem: Forests, ponds, and lakes.
ii. Human-made (artificial) ecosystem: Gardens, aquariums, and crop fields.
Q. No. 4) How will you create an artificial aquatic ecosystem, which is self-sustainable?
Ans. Preparation of a self-sustainable artificial aquatic ecosystem:
i. Take a large jar filled with water.
ii. Provide oxygen through an oxygen pump (aerator) and fish food that is
available in the market.
iii. Add aquatic plants and animals.
iv. Aquatic plants/Producers provide O2 during photosynthesis.
v. Aquatic animals/Consumers release CO2 for the process of photosynthesis.
vi. Decomposers are also important for the natural cleaning of the aquarium.
Q. No. 5) What is the role of decomposers in the ecosystem?
Ans. Role of decomposers in an ecosystem are:
i. They clean the environment.
ii. They decompose biodegradable substances into useful substances.
iii. They release nutrients into the soil by decomposing dead and decaying matter,
thus making the soil fertile.
iv. They maintain the nutrient pool by returning the nutrients in the pool.
Q. No. 6) What is the 10 percent law?
Ans. 10 percent law: Only 10% of energy is transferred to the next trophic level. The
remaining 90% of energy is used in life processes (digestion, growth, reproduction, etc.) by
the present trophic level.
Q. No. 7) a. Create a terrestrial food chain depicting four trophic levels.
b. Give a reason why a food chain cannot have more than four trophic levels.
Ans. a. Plant → Grasshopper → Frog → Snake
b. According to the 10% law, the amount of energy available will not be sufficient for the
survival of the organism in the 5th trophic level.

Q. No. 8) The flow of energy between various components of the environment has been
extensively studied. List four findings.
Ans. The flow of energy between trophic levels:
i. The flow of energy is unidirectional.
ii. Terrestrial plants take about 1% of the Sun’s energy and change it to chemical
energy.
iii. A great deal of energy is lost as heat/is used for digestion/ doing work/ growth
and reproduction.
iv. An average of 10% of the food eaten is turned into its own body and made
available for the next level of consumers.
v. Food chains are mainly of 3-4 trophic levels (because of the 10% law).
vi. The number of producers is maximum and the number reduces in subsequent
trophic levels.
vii. Food webs are more common as compared to isolated food chains.
viii. Biological magnification can be observed.
Q. No. 9) Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
Ans. The flow of energy generally is Sun → Producer → Hervibore → Carnivore. Since the
flow is progressively from one trophic level to another and does not revert back, it is said to
be unidirectional. Further, the available energy decreases in the higher trophic levels making
it impossible for energy to flow in the reverse direction.
Q. No. 10) Give the difference between a food chain and a food web.
Ans.
Food Chain Food Web

i. Food chain is a series i. Food web consists of a

of organisms feeding on number of interlinked
one another. food chains.

ii. Members of higher ii. Members of higher

trophic level feed upon a trophic levels can feed
single type of organism upon organisms of the
of the lower trophic lower trophic levels of
level. other food chains.

iii. It does not have any

iii. It improves the
effect on improving the
adaptability and
adaptability and
competitiveness of the
competitiveness of the
organism.
organism.

iv. Example: A hawk

might also eat a mouse,
iv. Example: Grass →
a frog, or some other
Grasshopper → Frog →
animal. The snake may
Snake → Hawk.
eat a beetle, a caterpillar,
or some other animal.

Q. No. 11) In the following food chain, vertical arrows indicate the energy lost to the
environment and horizontal arrows indicate energy transferred to the next trophic level.

Which one of the three vertical arrows (A, C, and E) and which one of the two horizontal
arrows (B and D) will represent more energy transfer? Give a reason for your answer.
Ans. A will represent more energy transfer as compared to C and E.
B will represent more energy transfer as compared to D.
When green plants are eaten by primary consumers (here Deer), a great deal of energy (here
represented by A) is lost as heat to the environment, some amount goes into digestion and in
doing work and the rest goes towards growth and reproduction. An average of 10% of the
food eaten is made available for the next level of consumers. This loss of energy takes place
at every trophic level.

Q. No. 12) Study the food web shown below.

a. Identify and write the food chain from the food web shown, in which the eagle will receive
the highest percentage of the energy from the producers.
b. Which organism will be the most affected when a non-biodegradable pesticide is
introduced into the soil? What is the phenomenon responsible for this called?
Ans. a. Grass → Mouse → Eagle.
b. The eagle will be the most affected.

Biomagnification (Accumulation of non-biodegradable pesticides in the food chain in

increasing amounts at each higher trophic level is known as biomagnification).

Q. No. 13) “Vegetarian food habits can sustain a larger number of people.” Justify the
statement in terms of the food chain.
Ans. Vegetarian food habits involve a two-step food chain, i.e., producers to herbivores.
According to the 10% law, energy flows from one trophic level to another. So vegetarians get
more energy than non-vegetarians. More energy in the producer plants can feed a larger
number of people. Thus, vegetarian food habits can sustain a larger number of people.
Q. No. 14) DDT was sprayed in a lake to regulate the breeding of mosquitoes. How would it
affect the trophic levels in the following food chain associated with a lake? Justify your
answer.
Ans. i. DDT being a non-biodegradable pesticide will enter the food chain from the first
trophic level i.e., Plankton.
ii. Non-biodegradable pesticides accumulate progressively at each trophic level. This
phenomenon is known as biological magnification.

iii. Hawk will have the highest level of pesticide.

Q. No. 15) The following organisms form a food chain.

Insect, Hawk, Grass, Snake, Frog.
Which of these will have the highest concentration of non-biodegradable chemicals? Name
the phenomenon.
Ans. Hawk. Biomagnification.
Q. No. 16) “Human beings occupy the top level in any food chain.” What are the
consequences of this on our bodies?
Ans. The consequences of human beings occupying the top level in any food chain are:
i. A maximum level of bio-magnification occurs here because of progressive
accumulation.
ii. We get a very small amount of energy as only 10% of the previous energy gets
transferred at each trophic level.
Q. No. 17) Gas A, found in the upper layers of the atmosphere (Stratosphere), is a deadly
poison but is essential for all living beings. The amount of this gas started declining sharply
in the 1980s.
a. Identify Gas A. How is it formed at higher levels of the atmosphere?
b. How is this Gas A both beneficial and damaging?
c. State the cause for the depletion of this gas. How can the depletion of this gas be
prevented?
d. State any two health consequences of ozone layer depletion on human health.
Ans. a. Gas A is Ozone (O3).
Formation of ozone:
The high-energy UV radiations break down the O2 molecules into free oxygen (O) atoms.

These oxygen atoms then combine with oxygen (O2) molecules to form the ozone molecule.

b. Ozone is beneficial as it shields the surface of the earth from UV radiations of the Sun.

Ozone is damaging as it is a deadly poison.

c. Cause of Ozone depletion: Synthetic chemicals like chlorofluorocarbons (CFCs) which are
used as refrigerants and in fire extinguishers lead to the depletion of the ozone layer.
Depletion of the ozone layer can be prevented by not using synthetic chemicals like CFCs,
that deplete the O3 layer.
d. Two health consequences of ozone layer depletion:
 • Skin Cancer
• Cataract
Q. No. 18) Why is damage to the ozone layer a cause for concern? What are its causes and
what steps are being taken to limit this damage?
Ans. Damage to the ozone layer is a cause for concern because the ozone layer shields the
surface of the earth from harmful UV radiations of the Sun which can:
i. Cause skin cancer, aging, and corneal cataracts in human beings.
ii. Result in the death of many phytoplanktons that lead to increased global
warming.
Causes of depletion: Synthetic chemicals like chlorofluorocarbons (CFCs) which are used as
refrigerants and in fire extinguishers lead to the depletion of the ozone layer.
Steps taken to limit the damage: Many developing and developed countries have signed and
are obeying the directions of UNEP (United Nations Environment Programme) to freeze or
limit the production and usage of CFCs at 1986 levels.
Q. No. 19) Differentiate between biodegradable and non-biodegradable substances. Cite
examples.
Ans.
Biodegradable Non-biodegradable
Substances Substances

i. Substances that are not

i. Substances that are
broken down by
broken down by
biological processes are
biological processes are
called non-
called biodegradable
biodegradable
substances.
substances.

ii. Examples – Wood, ii. Examples – Plastic,

paper, etc. DDT, etc.

Q. No. 20) “Improvements in our lifestyle have resulted in greater amounts of waste
generation.” Give two examples to support the given statement. Suggest one change that we
can incorporate into our lifestyle in order to reduce non-biodegradable waste.
Ans. More use of disposable items like paper plates, plastic items, polythene, etc.
Suggestion: Reuse polythene bags, and plastic containers.

Q. No. 21) A lot of waste is generated in the neighborhood. However, almost all of it is
biodegradable. What impact will it have on the environment or human health?
Ans. Excess generation of biodegradable wastes can be harmful as:
i. Its decomposition is a slow process leading to the production of foul smells
and gases.
ii. It can be the breeding ground for germs that create unhygienic conditions.
Q. No. 22) What are the problems caused by the non-biodegradable wastes that we generate?
Ans. The problems caused by non-biodegradable wastes are:
i. They cause biomagnification.
ii. They increase pollution.
 iii. They make the environment unclean.
iv. They kill useful microorganisms.
Q. No. 23) Suggest any four activities in daily life which are eco-friendly.
Or,
List three environmentally friendly practices which you would like to form a part of your
daily habits giving justification for each.
Ans. Eco-friendly activities are:
i. Walk or cycle for short distances to reduce the use of vehicles running on
fossil fuels.
ii. Use both sides of the paper to reduce its use. Fewer trees will be cut to make
more paper.
iii. Separation of biodegradable and non-biodegradable wastes.
iv. Gardening
v. Use of gunny bags/paper bags in place of polythene/plastic bags.
vi. Use of compost and vermicompost in place of fertilizers.
vii. Harvesting rainwater, etc.
Q. No. 24) Plastic cups were used to serve tea in trains in the early days – these could be
returned to the vendors, cleaned, and reused. Later, Kulhads were used instead of plastic
cups. Now, paper cups are used for serving tea.
What are the reasons for the shift from plastic to kulhads and then finally to paper cups?
Ans. The reasons for the shift from plastic to kulhads and then finally to paper cups are:
• The use of plastic cups raised the concern about hygiene thus they were
replaced by disposable plastic cups.
• Disposable plastic cups are non-biodegradable and harm the environment.
They were thus replaced by kulhads.
• Kulhads made of clay on a large scale resulted in the loss of top fertile soil.
• Now, disposable paper cups are used because – the paper can be recycled, is
biodegradable, and is an eco-friendly material that does not cause
environmental pollution.