EXPLANATIONS

Objective Questions

8. (b) In the given food chain, X could be small fish who feeds on

1. (b) Option (b) is incorrect pair and can be corrected as

zooplankton.

Air is abiotic (non-living) component of ecosystem.

Hence, X is a secondary consumer. Y acts on every trophic

2. (d) The flow of energy is not a functional component of an

level whichmeans it is a decomposer whoacts ondead remains

ecosystem.

of living organisms.

3. (a) Flow of energy in an ecosystem is always unidirectional.

9. (c) In the given pyramid of energy, T

1,^T2 ,^T3 andT4 represent

the trophic levels. T

1 representsplantswhichareproducers,

4. (b) In the given diagram,P represents producers as every food

e.g. grass, T₂

represents herbivores who are plant-eating

chain begins with plants which are autotrophic in nature.Qis

animals, e.g. deer. T₃ represents both carnivores or omnivores

primary consumer that depends on plants directly, i.e. they are

who feeds on plant-eating animals, e.g. bear. T₄ represents

herbivores.

tertiary consumers who feed on other animals, e.g. lion,

R could be carnivores or omnivores and acts as secondary

Hence, option (c) is correct.

consumer in the food chain as it depends upon plant eating

10. (c) C represents the correct pyramid in a food chain.

animals.

Population of producers (plants) are maximum in a food chain

S are decomposers that help in cleaning our environment by

to support other animals. As the trophic level increases, the

acting on dead and decaying organic matter and decompose

number of organisms decreases.

them into soil.

11. (c) The given food web contains various food chains

Thus, option (b) gives correct identification and main function

interconnected with each other.

or characteristic.

Frog, bird and fish act as secondary consumers in their

5. (a) The given food chain is as follows

respective food chains, therefore acquire same trophic level ,

Grass → Grasshopper → Frog → Snake → Hawk

i.e. third trophic level in their respective food chain.

12. (a) Biomagnification is the phenomenon of progressive

A. Grass acts as producer in the given food chain as it is

increase in the concentration of non-biodegradable toxicants

autotrophic in nature and make its own food in the

in organisms at each successive trophic level. It is also called

presence of sunlight. All living organisms depend upon

bioconcentration.

plants directly or indirectly.

13. (c) The layerP is ozone layer that protects us from harmful UV

B. Grasshoppers are primary consumers as they feed on

rays of Sun. Chlorofluorocarbon is responsible for depletion of

plants (grass) directly.

ozone layer.

C. Frogs are primary carnivores as they feed on plant-eating

animals (grasshoppers).

14. (a) High energy UV radiations split apart molecular

D. Snakes are secondary carnivores as they eat flesh of other

oxygen (O )

into free oxygen atoms (O) which are highly

animals and feed on primary carnivores majorly.

reactive and combine with molecular oxygen to form ozone

Thus, option (a) is correct.

layer.

6. (d) If deer is missing in the given food chain, there will not be

15. (d) Incineration involve degradation of wastes by burning

sufficient food for the tigers. Some of the tigers will die

them at high temperature.

because of starvation and hence, the population of tigers will

16. (c) A is true, but R is false.

decrease. Since grass is eaten by deers, the population of grass

will also increase when deer is missing.

All living organisms are biotic components of ecosystem

whereas all non-living things such as wind, gases, light, water,

7. (c) In a food chain, only around 10 % of the available energy is

etc., are abiotic components of ecosystem.

passed on to the next trophic level. The rest of the energy is lost

to the ecosystem in form of heat.

17. (d) A is false, but R is true.

As the trophic level increases, the amount of energy transfer

Food chains generally consist up to three or four trophic levels

decreases.

because there is loss of energy at each trophic level and very

little usable energyremainsafter three or four trophiclevels.

Secondary consumers receive the smallest amount of energy

18. (c) A is true, but R is false.

from primary consumers.

Hence, arrow 2 shows smallest energy transfer, whereas arrow

Autotrophs (producers) are present at the first trophic

3 shows largest energy loss as 90% of energy at producer level

level because they fix solar energy, making it available for

is lost to the ecosystem, whereas only

10% of energy is

consumers or heterotrophs.

transferred to the primary consumers.

19. (c) A is true, but R is false.

(iii)

(a) Solid waste R completely decomposes in very few days

Certain pesticides and other chemicals used to protect

whichmeansit isaneasilydecomposable biodegradable waste.

our crops from diseases and pests do not get degraded

e.g. Cow dung, fruit pulp, etc.

(i.e. non-biodegradable). So, they get accumulated

(iv) (a) Non-biodegradable waste can be decomposed

progressively at each trophic level.

by recycling or by dumping underground into landfills.

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

(v) (c) Incineration is a method of waste disposal in which

of A. Ozone layer is present in the stratosphere region of

burning of substances take place at high temperature to form

our atmosphere. It shields the surface of Earth from

ash. It is used to dispose off hospital or harmful wastes of

harmful UV radiations of Sun which are highly damaging

biomedical industries.

and can cause various health issues and diseases such as

Subjective Questions

skin cancer, cataract, etc.

1. Ecosystem is defined as the structural and functional unit of

21.

(i)

(b) Due to biomagnification, the concentration of

biosphere. It is a stable ecological unit where continuous input of

harmful chemicals such as DDT increases at each

energy and circulation of matter occurs.

successive trophic level.

The maximum concentration of DDT gets

Top carnivores

accumulated in Z and least is found in Y.

Therefore, the correct order of animals in food chain

Carnivores

is Y → W → X → Z.

Herbivores

(ii)

(a) The concentration of DDT is found to be less in

organisms of lower trophic level and higher in

organisms of higher trophic levels.

Producers

If the amount of DDT in W is estimated to be 0.4

ppm then in Y, it has to be less than 0.4 ppm, i.e.

Sunlight

0.02 ppm and in Z, it has to be more the 0.4 ppm, i.e

Flow of energy in an ecosystem

2 ppm.

Hence, option (a) is correct.

(i) Ecosystem is the structural and functional unit of biosphere

(iii)

(b) The progressive increase in the concentration of

and is a stable ecological unit where regular input of energy

non-biodegradable toxicants in organisms at each

and circulation matter takes place.

successive trophic level is known as

(ii) Autotrophs can make their own food in the presence of

biomagnification.

sunlight. They are the ultimate source of energy for each and

every organism of a food chain. Hence, every chain always

(iv)

(a) Decomposers are microorganisms that

starts with producers (autotrophs) that is why they are placed

breakdown dead and decayed organisms into

at the first trophic level of food chain.

simpler inorganic materials, making nutrients

(iii) In given food chain, Grass→ Insects→ Frogs→ Snakes

available to primary producers. They act at every

Frogs assign at third trophic level. They acts as secondary

trophic level of the food chain.

Hence, they do not have a fix position in the food

consumers who feeds of primary consumers (i.e. insects).

chain.

3. Organisms that feed on dead plants and animals are called

(v)

decomposers, e.g. bacteria, fungi, etc. They breakdown the

complex organic compounds present in the dead remains into

substances such as pesticides, fertilisers and heavy

simpler substances and obtain nutrition from them. These

metals are hazardous to the environment, whereas

substances are released into the soil and to the atmosphere.

manures are organic substance made by

decomposing dead and decayed living organisms

Thus, they play the following roles

buried under the soil.

(i) They help in recycling of materials, replenishment of the

22.

(i)

(b) S is the solid waste that does not decompose at

soil’s nutrients, etc.

all. According to the graph, there is no change in

(ii) They clean our surroundings by decomposing dead organisms

number of days for the amount of decomposition

and organic wastes.

take place in S waste.

4. Natural water bodies are example of natural ecosystem. They

Hence, it is a non-biodegradable waste.

exist naturally without any human support, whereas aquarium is

(ii)

(b) Substances which do not decompose by the

an artificial ecosystem which is created and maintained by

action of microorganisms present in the soil are

humans. It rely on human efforts to sustain. It does not possess a

known as non-biodegradable substances.

self-regulating mechanism.

They enter into food chain through soil and get

5. The study of food chain in an area or habitat helps in

magnified into higher trophic levels. In soil, they

(i) understanding the energy transfer through organisms.

also cause pollution which decreases the soil

(ii) understanding the ecological balance in a habitat or

fertility.

ecosystem.

(iii) understanding harmful human activities and disruption

11. The flow of energy in an ecosystem occurs in the following

of ecological balance, if any.

sequence

An example of four steps of food chain operating in a large lake

Sun ⎯→ Producer ⎯→ Herbivore

⎯→

Carnivore

is as follows

(Primary

(Secondary

consumer)

Algae → Protozoan → Small fish → Big fish.

The flow of energy is unidirectional because of the reasons

6. Parasites are organisms (animals or plants) that live in or an

given below

other organism (host) and take benefits by deriving nutrients

(i) Energy flows progressively from one trophic level to

from it, i.e. they get food or protection from host organism, e.g.

another and cannot revert back. Energy given out as

Cuscuta.

heat is lost to the environment and does not return to be

On other hands, decomposers are organisms that breakdown

used again.

dead or decaying organisms into simple inorganic

(ii) The available energy decreases at higher trophic level.

substances. e.g. Fungi.

Out of the total energy available at a particular trophic

7. The transfer of food or energy takes place through various

level, only 10% is passed on to the next trophic level,

levelsinthe food chain,whichare knownastrophiclevels.e.g.

making it impossible for energy to flow in the reverse

Trees

→ Rabbit

→ Snake

→ Hawk

direction.

(First trophic

(Second trophic

(Third trophic

(Fourth trophic

12. Biological magnification also known as biomagnification is the

level)

phenomenon of progressive increase in the concentration of

[Producers]

[I consumer]

[II consumer]

[III consumer]

non-biodegradable toxicants in organisms at each successive

trophic level.

8. In a food chain, about 80-90% of the energy available at a

trophic level is lost during its transfer to next trophic level.

13. Biological magnification refers to the increase in the

Hence, amount of energy available goes on decreasing at each

concentration of certain toxicants at each successive trophic

successive trophic level.

level.

If a plant fixes 4000 J energy, then next three successive

No, the levels of magnification will not be same in all trophic

trophic levels will get

400 J,

40 J and 4 J, respectively

levels. When the chemicals do not get degraded and get

(according to 10% law). If another level is added in a food chain

accumulated progressively at each trophic level, it leads to

then it will get only 0.4 J energy. Thus, usually food chains

biomagnification. Biomagnification is more in organisms of

remain shorter and limited to 3-4 trophic levels only.

higher trophic levels.

9. Ifwekillalltheorganismsinonetrophiclevel,thelowertrophic

14. Depletion of ozone is mainly caused due to the excessive use of

level will grow more in number and the higher trophic level will

Chlorofluorocarbons (CFCs). These are synthetic chemicals

not survive.

which are used as refrigerants and in fire extinguishers.

Hence, flow of energy from one trophic level to other will not

Steps which should be taken to limit the damage to ozone layer

take place.

include

(a) Minimising the use of aerosol spray propellants containing

10. According to 10% law, only 10% of the energy entering a

fluorocarbons and chlorofluorocarbons.

particular trophic level of organisms is available for transfer

(b) Exercising control over large scale nuclear explosions

to the next higher trophic level.

and limited use of supersonic planes.

The flow of energy through a food chain is unidirectional and it

15. Ozone layer filter the Sun's ultraviolet radiation

(UV-B),

moves progressively through various trophic levels as follows

thereby protecting the environment from its harmful effects

(i) Green plants capture 1% of energy of the sunlight that

and also play key role in regulating the temperature.

falls on their leaves and convert it into food energy.

16. The energy and biomass decrease from lower to higher trophic

(ii) When green plants are eaten by primary consumers, a

levels, so the length of food chain is restricted and cannot have

great deal of energy is lost as heat to the environment.

more than four trophic levels.

On an average only 10% of food eaten is turned into its

own body and made available for the next level of

17.

(i) UV radiation acts on the O₂ molecule. Higher energy of

consumers.

UV split apart O₂.

(iii) Thus, 10% can be taken as average value of the amount

(ii) O

⎯ ⎯→

O+O

of organic matter present at each step and reaches the

O+O

⎯→

next level of consumers.

(Ozone)

Leaf

10% energy

Caterpillar

(iii) CFCs rise up in stratosphere where UV radiation splits

Sun

(producer)

transferred

(primary consumer)

them releasing molecular chlorine (Cl

−

). It reacts with

O₃ and releases oxygen, so O₃ gets depleted.

10% energy

Snake

Bird

18. Ozone at the higher levels of the atmosphere is a product of UV

(tertiary consumer )

transferred

(secondary consumer)

transferred

radiations acting on oxygen (O )

molecule. The high energy UV

Energy lost by energy transfer

radiations split apart some molecular oxygen (O )

into free

oxygen (O) atoms. These atoms are very reactive and combine

24. Effective segregation of waste as biodegradable and

with the molecular oxygen to form ozone.

non-biodegradable is much easier to recycle. Biodegradable

waste used to make manure can out of compost, whereas

O ⎯→ O + O

non-biodegradable waste could be recycled and reused for

O + O

⎯→

various purposes. Also effective segregation of wastes means

(Ozone)

that less waste goes to landfill, which makes it cheaper and

It shields the surface of the Earth from harmful ultraviolet

better for people and environment.

(UV) radiations of the Sun.

25. A pond ecosystem refers to freshwater ecosystem where

Due to environmental pollution, ozone layer has began to

there are various organisms dependent on each other with

deplete in the 1980s.

the prevailing water environment for their nutrients and

survival.

This was mainly due to the increasing use synthetic

chemicals like Chlorofluorocarbons (CFCs). These are used

Phytoplankton→ Zooplankton→ Small fish → Big fish

in refrigerants as coolant and in fire extinguishers.

There are two components of the pond ecosystem

Due to depletion of ozone layer harmful UV rays can

(i) Abiotic It includes water, dissolved minerals, oxygen

penetrate or enter our atmosphere.These radiations are

and carbon dioxide. Sunlight is the main source of

highly damaging to organisms. They can cause skin cancer in

energy.

human beings, damage eyes (cause disease called cataract),

(ii) Biotic It consists of phytoplanktons, zooplanktons,

decrease crop yield, disturb global rainfall, etc.

aquatic insects, fishes and other aquatic animals. These

19. Following methods could be applied to reduce the

organisms are classified as producers, consumers and

accumulation of pesticides in our body.

decomposers.

(i) Minimise the use of pesticides

26. The waste generated in our house and measures for its disposal

(ii) Consuming washed fruits and vegetables

are given in the table below

(iii) Developing vegetarian feeding habits

Household wastes

Measures for disposal

(i.e. feed upon plants as plants belong to lower trophic level so,

they have less accumulation of insecticides, whereas

Kitchen waste like bottles, Prepare a compost pit

organisms of higher trophic level have higher concentration of

plastics, food, etc.

insecticides and pesticides).

Paper wastes like

Should be recycled

20. We can reduce the problem of waste disposal by the following

newspaper, envelopes, etc.

methods

^● Recycling The solid wastes such as paper, plastics, glass

Plastic bags

Should be safely dumped in

and metals, etc., are recyclable. So, waste paper can be sent

garbage bins for

non-biodegradable wastes

to paper mills for reprocessing to form newspaper. The

plastic articles can be melted and remoulded again to make

Vegetable/fruit peels/rind Can be placed near trees/plants,

new articles.

so that on decomposition enrich

^● Biodegradable waste The waste such as left over food,

the soil with nutrients

fruits, animal dung, peels of vegetables can be converted

All other wastes

Segregation into biodegradable

into compost by burying them in a pit dug in ground and

and non-biodegradable wastes

can be used as manure.

21. If all the waste is biodegradable, then there will be no

27. Insecticides are non-biodegradable chemicals added to crop

accumulation of waste on the Earth and it would be a cleaner

fields to stop the growth of insects infecting the crops.

place to live.

Modern insecticides are being developed keeping in

But if, this biodegradable waste is too large in amount then its

mind, the harm they cause to the environment and its

slow degradation may lead to air pollution (due to release of

components.

gases) as well as water and land pollution.

Biodegradable insecticides can be decomposed into harmless

22. The two ways in which non-biodegradable substances would

substances, which will subsequently be dispersed in their

affect the environment are

specific pathways and cause no pollution.

(i) They make the environment poisonous and unfit for

Non-biodegradable insecticides build up in the fat tissues of

survival of living forms of life.

the body and pass on to organisms that feed on them.

(ii) They block the transfer of energy and minerals in the

ecosystem.

Hence, they accumulate along the food chain resulting in

23. Biodegradable materials are broken down by microorganisms

significant amounts in the tissues of consumers at the

present in nature into simple harmless substances.

highest trophic level.

Non-biodegradable materials need a different treatment like

The property of newly developed insecticide includes that it

heat and temperature for disposal and hence, both should be

can easily get decomposed into simpler components by soil

discarded in two different dustbins.

bacteria.

So, the energy that is captured by the producers does

28. As Mona follows vegetarian diet along with milk products.

not revert back to the Sun and the energy transferred to

She should be considered as occupying third trophic level

the herbivores does not come back to the producers. It

because the curd is prepared by the milk of cow/buffalo by

just keeps on moving to the next trophic level in one

the action of bacteria, but the energy of the milk is getting

direction. That is why the flow of energy in the food

transferred from cow to Mona, so Mona is at the third

chain is always unidirectional.

trophic level.

(ii)

A large number of pesticides and chemicals are used to

Grass

⎯⎯⎯→ Cow (milk) ⎯⎯⎯→ Human

protect our crops from pests and diseases. Some of these

(First trophic level)

(Second trophic level)

(Third trophic level)

chemicals are washed down from the soil, while some

29. Organisms which breakdown the complex organic compounds

enter the water bodies. From the soil, they are absorbed

present in dead and decaying matter into simpler inorganic

by plants along with water and minerals and from the

materials are called decomposers, e.g. certain bacteria and

water bodies, they are taken up by aquatic plants and

fungi.

animals. This is how these chemicals enter the food

chain.

Decomposers act as cleaning agents of environment by

As these chemicals cannot decompose, they accumulate

decomposing dead bodies of plants and animals. They also

progressively at each trophic level. This increase in the

help in recycling of materials, replenishment of soil’s

concentration of harmful chemicals with each step of the

nutrients, etc.

food chain is called biomagnification. As human beings

The consequence of their absence in an ecosystem can be

occupy the top level in any food chain, these chemicals

disastrous. The dead bodies would persist for long, leading

get accumulated in our bodies in considerably high

to their accumulation and thus, polluting the environment.

amount causing diseases.

The biogenetic nutrients associated with these remains will

33.

(i)

Undesirable activities of man eliminate growth of

not be returned back to the environment.

organisms belonging to one or more trophic levels in a

As a result, all the nutrients present in soil, air and water

food chain. Thus, the food chain gets shortened, e.g.

would soon be exhausted and the whole life cycle of

hunting tigers for their skin, etc.

organisms will be disrupted.

It causes imbalance in the functioning of ecosystem and

30.

(i)

Consumers are the organisms who derive energy by

biosphere. If organisms of one trophic level are

eating plants or other organisms as they cannot produce

eliminated, the organisms prior to that trophic level will

food on their own. Absence of primary consumers in

flourish and increase in number. Also, the organisms of

nature would lead to enormous growth of plants and

the subsequent trophic level will sharply decrease,

decline in the population of carnivore animals, who eat

thereby creating an imbalance.

them. Hence, the whole food web will get distrupted.

(ii)

Vegetarian food chain is advantageous in terms of energy

(ii)

The direction of energy transfer in following cases are as

because it has less number of trophic levels. As we know,

follows

only 10% of the energy is transferred to the next trophic

(a) Primary consumer (grasshopper) to secondary

level in a food chain, so if a person is vegetarian then, he

consumer (frog).

would have maximum amount of energy by consuming

(b) Producer (grass) to primary consumer (deer).

producers or plants in a food chain.

34. Some harmful effects of agricultural practices on the

(lion).

environment are as follows

31.

(i)

Yes, the impact of removing all the organisms in a

(i) Soil degradation Extensive cropping causes loss of soil

trophic level will be different for different trophic levels.

fertility. Also, over the time it can lead to soil erosion

The lower trophic level of an ecosystem has a greater

and finally to desertification.

number of individuals than the higher trophic levels.

(ii) Pollution Use of synthetic chemical fertilisers and

Removal of producers will affect all the organisms of

pesticides leads to soil, water and air pollution.

successive trophic levels and it will threat their survival.

(iii) Water shortage Excess use of groundwater for

The removal of higher trophic level will lead to increase

agriculture lowers the water level. This results in acute

in organisms of lower trophic level and the organisms of

water shortage at many places.

higher trophic level will die due to the shortage of food.

(iv) Biomagnification The chemical pesticides, being

(ii)

No, removal of all organisms of a trophic level will

non-biodegradable accumulate in organisms in

disturb the ecosystem. Killing of higher trophic level

increasing amounts at each trophic level.

organisms will cause explosion in the population of lower

(v) Deforestation Indiscriminate cutting of trees for

trophic level organisms. This will adversely affect the

agriculture has resulted in loss of habitat for wildlife.

ecosystem and thus environment.

Thus, it also causes damage to natural ecosystem.

32.

(i)

The producers convert solar energy into chemical energy

35. Ozone is a triatomic molecule, i.e. made up of three atoms of

in the form of organic compounds. The primary consumers

oxygen joined together. Its molecular formula is O₃ . It can

(herbivores) derive their nutrition from the producers.

affect any ecosystem in the following ways

According to the energy transfer law, only 10% of energy is

(i) It protects against ultraviolet rays if, present in

transferred from one trophic level to the other.

stratosphere.

(ii) Ozone dissipates the energy of UV rays by undergoing

(v) Use compost Instead of using synthetic fertilisers,

dissociation followed by reassociation.

compost provides a full complement of soil organisms

and the balance of nutrients needed to maintain the

O ⎯→ O + O

; O

⎯→

(Ozone)

soil’s health. Healthy soil minimises the population of

(iii) In atmosphere, it is highly toxic and causes injury to

weeds.

mucous membranes, eye irritation and internal

38. Materials that remain for a long time in the environment,

haemorrhages in animals and humans.

without getting decomposed by any natural agents, also

causing harm to the environment are called

36.

(i) Environmental pollution is an undesirable change in the

non-biodegradable. Plastic cups are non-biodegradable and

physical, chemical or biological characteristics of the

raised the concern towards hygiene, thus they were

natural environment, brought about by man’s activities.

replaced by kulhads.

This pollution may affect the soil, water or air.

Kulhads are made up of clay on a large scale resulted in the

(ii) Differences between biodegradable and

loss of top fertile soil. It is replaced by disposable paper

non-biodegradable pollutants are as follows

cups because the paper can be recycled, it is biodegradable

Biodegradable

Non-biodegradable

and is eco-friendly material which does not cause

pollutants

environment pollution.

(i)

39.

There are 6 food chains that constitute to form the

These pollutants can be

These pollutants cannot be

given food web. These are as follows

broken down into non-toxic

substances in nature by the

substances by microorganisms.

1. Seeds → Mice → Foxes

action of microorganisms.

2. Young trees → Mice → Foxes

3. Young trees → Rabbits → Foxes

They get recycled thus, do They cannot be recycled thus,

4. Grass → Rabbits → Foxes

not need any dumping sites. require dumping sites.

5. Grass → Rabbits → Snake

They cause minimum

They cause maximum

6. Young trees → Rabbits → Snake

environmental pollution.

(ii)

The primary consumers are the organisms who directly

feed on the producers. In the given food web, rabbits

(iii) Non-biodegradable pollutants include DDT, radioactive

and mice are the primary consumers, whereas foxes and

waste, plastic, insecticides.

snake are the secondary consumers.

37. Some daily life eco-friendly activities are

(iii)

About 90% of energy is loss at each trophic level.

(i) Save a tree, use less paper You can buy ‘tree-free’ 100%

(iv)

The foxes feed on the rabbits and mice. If all the foxes

are killed then there will be no direct predator of

post-consumer recycled paper for everything from

rabbits and mice, hence the number of rabbits and mice

greeting cards to toilet paper. Paper with a high

(i.e. both are primary consumers) will increase in the

post-consumer waste content uses less pulp and keeps

given ecosystem, which will disturb its balance.

more waste paper out of landfills.

(v)

Accumulation of toxic non-biodegradable substances

(ii) Opt bamboo for hardwood floors Bamboo is considered

increases at each trophic level. It is least in organisms

as an environmental-friendly flooring material due to its

of first trophic level (i.e. seeds), young trees and grass

high yield and the relatively fast rate at which it

and highest in organisms of third trophic level (i.e. foxes

replenishes itself. It takes just 4-6 years for bamboo to

and snake).

mature, compared to 50-100 years for typical hardwoods.

40.

(i)

The green plants in a terrestrial ecosystem capture

Also look for sources that use formaldehyde-free glues.

about 1% of the energy of sunlight (light energy). They

(iii) Reduce plastics, reduce global warming Unfortunately,

convert it into food energy (chemical energy).

plastics are made from petroleum, the processing and

Therefore, if 10,000 J solar energy falls on green plants in

burning of which is considered one of the

a terrestrial ecosystem, only 1% of solar energy, i.e. 100 J

main contributors to global warming, according to the

will be converted into food energy.

EPA. In addition, sending plastics to the landfill also

(ii)

Decomposers are not included in the food chain as they

increases greenhouse gases. Reduce, reuse and recycle

act at every trophic level of the food chain.

our plastics are one of the best ways to combat global

warming.

(iii)

Primary consumers are those organisms who directly

feed on plants, e.g. herbivores.

(iv) Use healthier paints Conventional paints contain

Primary carnivores are those organisms who feeds on

solvents, toxic metals and Volatile Organic Compounds

plant-eating animals, e.g. snake.

(VOCs) that can cause smog, ozone pollution and indoor

(iv)

Decrease in energy at higher trophic levels (according to

air quality problems with negative health effects,

10% law) is one of the main reason that limits the number

according to the EPA. These unhealthy ingredients are

of trophic levels in a food chain.

released into the air, while we are painting, drying of paint

and even after the paints are completely dry.

(v) Owl is placed at highest trophic level in the given food

42.

(i) Substances that are responsible for depletion ozone layer

web, therefore the accumulation of non-biodegradable

or breakdown of ozone molecules are known as ozone

toxic materials are found to be highest in them due to

depleting substances.

biomagnification.

e.g. CFCs, halogens, nitrous oxide,CCl₄andCH₄ are ozone

41.

(i) The longest food chain consist of maximum five trophic

depleting substancesresponsible for ozone layer depletion.

levels.

(ii) Atomic oxygen is highly reactive. It combines with

(ii) Rabbit is a herbivore as it feeds on plants directly. Its

molecular oxygen to form ozone.

role in the given food web is to transfer the energy from

⎯VU

[O] + [O]

producers to carnivores.

+ 2 [O] ⎯→

(Ozone)

(iii) The significance of food web is as follows

(iii) Ozone layer is found in the stratosphere around 15-30 km

(a) Food chain provides pathways for availability of

above the Earth’s surface.

food.

(iv) Ozone is a triatomic molecule made up of three atoms of

(b) It allows endangered populations to grow in size.

oxygen (O₃ ). It is present in atmosphere as an ozone layer

(iv) Sun or solar energy is the ultimate source of energy for

shield that protects us from high energy UV radiations.

the Earth. Only plants can utilise this energy to make

So, it is known as good ozone whereas near the surface of

their on food.

earth ozone act as a highly poisonous gas. Hence, known

(v) When predator for a particular organism decreases in

bad ozone.

number, the organisms start increasing in number.

(v) Cancers, mutations, effect on eyesight, global warming,

As the animals which used to feed on them decrease in

weakening of immune system, etc., are some adverse

number, therefore, the population of those organisms

effects of ozone depletion.

increases.