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Page No 226:

Question 20:

Explain the terms 'producer' and 'consumer'. Give two examples of producers and two of consumers.

Answer:

Organisms that produce their own food from simple inorganic substances such as water and carbon dioxide are called producers. Examples are green plants and blue-green algae.
Organisms that consume the food prepared by producers are called consumers. Examples are cows and human beings.

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Question 21:

(a) Define decomposers. Name one decomposer.
(b) What is the role of decomposers in the ecosystem?

Answer:

(a) Micro-organisms that break down the complex organic compounds present in dead plants and animals and their products, such as faeces and urine, into simpler substances are called decomposers. Bacteria are decomposers.

(b) Decomposers decompose dead plants and animals and hence act as cleansing agents of the environment.

Page No 226:

Question 22:

What is meant by a primary consumer, secondary consumer and a tertiary consumer? Give one example of each.

Answer:

Herbivores that feed on plants are called primary consumers. Example: Insects.
Small carnivores that feed on other animals, especially herbivores, are called secondary consumers. Example: Frogs.
Large carnivores that feed on other animals, especially secondary consumers, are called tertiary consumers. Example: Birds.

             Insects                        Frogs                                   Birds
(Primary consumers)       (Secondary consumers)         (Tertiary consumers)

Page No 226:

Question 1:

What is the functional unit of the environment comprising of the living and non-living components called?

Answer:

The functional unit of the environment consisting of living and non-living components is called an ecosystem.

Page No 226:

Question 2:

Name two natural ecosystems and two artificial ecosystems.

Answer:

Two natural ecosystems are the pond ecosystem and the forest ecosystem. Two artificial ecosystems are the crop field ecosystem and the aquarium ecosystem.

Page No 226:

Question 3:

Which one of the following is not a terrestial ecosystem?
forest, Grassland, Aquarium, Desert

Answer:

Among the given ecosystems, an aquarium is not a terrestrial ecosystem.

Page No 226:

Question 4:

Why are plants called producers?

Answer:

Plants are known as producers because they prepare their food themselves by the process of photosynthesis.

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Question 5:

What name has been given to those organisms which break down the complex organic compounds present in dead animals and plants?

Answer:

Organisms that break down the complex organic compounds present in dead animals and plants are called decomposers.

Page No 226:

Question 6:

What are planktons?

Answer:

The tiny herbivorous plants and animals present in water are known as plankton. Plankton are classified as phytoplankton (plants) and zooplankton (animals).

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Question 7:

State whether the following statements are true or false :
(a) In biology, human beings are called producers.
(b) Secondary consumers and tertiary consumers, both are carnivores.

Answer:

(a) False. Green plants are known as producers.
(b) True.

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Question 8:

Which category of organisms forms the starting point of a food chain?

Answer:

Producers (green plants) form the starting point of a food chain.

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Question 9:

Which of the following belong to the same trophic level?
Goat ; Spider ; Plants ; Hawk ; Rat

Answer:

Goats and rats belong to the same trophic level as they are both herbivorous animals.

Page No 226:

Question 10:

Which of the following belong to the same trophic level?
Tree ; Frog ; Snake ; Grass ; Lizard

Answer:

Trees and grass belong to the same trophic level as they are both producers.

Page No 226:

Question 11:

Write an aquatic food chain.

Answer:

A food chain that operates in a water body, such as a pond, a lake or an ocean, is known as an aquatic food chain.

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Question 12:

Name the organisms belonging to the second and the fourth trophic levels in the food chain comprising the following :
Frogs, Plants, Snakes, Hawk, Insects

Answer:

The second trophic level consists of insects, and the fourth trophic level consists of snakes.

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Question 13:

What are the various steps of food chain called?

Answer:

The various steps of a food chain are called trophic levels.

Page No 226:

Question 14:

Construct a food chain comprising the following :
Snakes, Hawk, Rats, Plants

Answer:

Plants  Rats  Snakes  Hawks

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Question 15:

Arrange the following in a food chain :
Fish, Algae, Small animals, Big Fish

Answer:

Algae  Small animals  Fish  Big fish

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Question 16:

Which organisms belong to third and fourth trophic levels in the food chain comprising the following?
Rats, Plants, Hawk, Snakes

Answer:

Snakes belong to the third trophic level and hawks belong to the fourth trophic level in the food chain.

Page No 226:

Question 17:

Which one term in the following includes the others?
air, flora, fauna, environment, water, sunlight, soil

Answer:

Environment is the term that includes the others, i.e., air, flora, fauna, water, sunlight and soil.

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Question 18:

A food chain represents a unidirectional flow of X. What is X?

Answer:

A food chain represents a unidirectional flow of energy. 
X is energy.

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Question 19:

Fill in the following blanks with suitable words :
(a) Decomposer organisms are..........in their action.
(b) In nature, all green plants are............ whereas animals are consumers.
(c) A series of organisms, each of which feeds on the next organism, the beginning of which is a green plant, is called a .............
(d) The science that deals with the inter-relationships of living things with one another and their environment is called...........
(e) Plastic is a ...............material whereas paper is a.............material.

Answer:

(a) Decomposer organisms are specific in their action.
(b) In nature, all green plants are producers, whereas animals are consumers.
(c) A series of organisms, each of which feeds on the next organism, the beginning of which is a green plant, is called a food chain.
(d) The science that deals with the inter-relationships of living things with one another and their environment is called ecology.
(e) Plastic is a non-biodegradable material, whereas paper is a biodegradable material.



Page No 227:

Question 23:

Give an example of a four step food chain operating in grassland. Name the secondary consumer in this food chain

Answer:

Grass Insect  Frog  Eagle

The secondary consumer in this food chain is the frog.

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Question 24:

(a) Define trophic level. Draw the food chain with four trophic levels.
(b) What will happen if we kill all the organisms in one trophic level?

Answer:

(a) The various steps in a food chain at which the transfer of food and energy takes place are known as trophic levels.
A food chain with four trophic levels can be shown as follows.
Grass Insect  Frog Eagle

(b) If we kill all the organisms in one trophic level, there will be no food for the organisms of the next trophic level, and they will die of starvation. Also, the organisms of the previous trophic levels will increase in number as there will be no organism to consume them as food.

Page No 227:

Question 25:

What is the difference between the food habits of organisms belonging to the first and the third trophic levels? Give one example each of the organisms belonging to these two trophic levels.

Answer:

First trophic level Third trophic level
Producers belong to the first trophic level. Carnivores belong to the third trophic level.
They prepare their own food by photosynthesis. They consume the flesh of other animals.
Example: Green plants. Example: Lions.

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Question 26:

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

Answer:

No, the organisms of no trophic level can be removed without causing damage to the ecosystem, as removing them can disturb the food chain.
Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels. Suppose the producers, who belong to the first trophic level, are removed, no organism belonging to the higher trophic levels will be able to exist, as the food and energy for the higher trophic levels are provided by the producers.
If consumers such as deer are removed from their trophic level, consumers such as lions, which eat deer, will die because of the unavailability of food. Hence, the population of lions will be reduced.
If consumers such as lions are removed from their trophic level, then there will be no predator control over the population of deer. Thus, the deer population will increase, leading to an excessive grazing of grass.

Page No 227:

Question 27:

Consider the food chain :
Grass → Deer → Lion
What will happen if all the lions are removed from the above food chain?

Answer:

If all the lions are removed from the above food chain, the population of deer will increase greatly, as there will be no lion to consume them as food. Also, the density of grass will decrease as the high population of deer will lead to excessive grazing of grass.

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Question 28:

The number of malaria patients in a village increased tremendously when large number of frogs were exported from the village. What could be the cause for it?

Answer:

As frogs were exported from the village, the mosquito population increased, because there were no frogs to consume the mosquitoes. Hence, the increased number of mosquitoes led to an increase in the number of malaria patients.

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Question 29:

How does a biodegradable waste differ from a non-biodegradable waste? Give two examples of non-biodegradable wastes which pollute our environment.

Answer:

Biodegradable waste Non-biodegradable waste
Waste materials that can be broken down into non-poisonous substances in due course of time, by the action of natural micro-organisms such as certain bacteria, are called biodegradable wastes.
 
Waste materials that cannot be broken down into non-poisonous or harmless substances naturally are called non-biodegradable wastes. 

 
Examples: Paper and vegetable peels. Examples: Plastic and iron nails.

Plastic and polythene bags are non-biodegradable wastes that pollute the environment.

Page No 227:

Question 30:

Which of the following are biodegradable and which non-biodegradable?
Glass bottle, Paper, Ball point pen refill, Hay, DDT, Wheat, Cake, Wood, Polythene bag, Jute bag, Cotton cloth, Grass, Vegetable peels

Answer:

Biodegradable: Paper, hay, wheat, cake, wood, jute bag, cotton cloth, grass, vegetable peels.
Non-biodegradable: Glass bottle, ballpoint pen refill, DDT, polythene bag.

Page No 227:

Question 31:

(a) Describe an activity to show that while paper is biodegradable but plastic (say, polythene) is non-biodegradable.
(b) Explain why, some materials are biodegradable but some are non-biodegradable.

Answer:

(a) An activity to prove that paper is biodegradable and plastic is non-biodegradable is described below.
1) Take a piece of paper and a polythene bag.
2) Dig a hole in the ground about 15 cm deep and place both the paper and the polythene bag separately in it. Cover them with soil.
3) Leave them for about one month.
4) On uncovering the buried materials, it will be observed that the paper has been partially eaten up by micro-organisms, whereas the polythene bag has remained unaffected. This proves that paper is biodegradable, whereas plastic is non-biodegradable.

(b) Some materials are biodegradable, whereas some are non-biodegradable, because decomposers break down natural materials such as paper but do not break down man-made materials such as plastics. Non-biodegradable materials consist of compounds that are not degraded by decomposers, and they persist in the environment.

Page No 227:

Question 32:

Write down a food chain :
(a) in the sea
(b) which ends with humans
(c) with five links in it.

Answer:

(a) Algae Protozoa Small fish Large fish

(b) Grass Goat Man

(c) Grass Grasshopper Frog Snake Eagle

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Question 33:

At which trophic level a person is feeding when he is eating :
(a) roasted chicken
(b) bread
(c) eggs
(d) apple
(e) fish

Answer:

(a) Third trophic level
(b) Second trophic level
(c) Third trophic level
(d) Second trophic level
(e) Fourth trophic level

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Question 34:

A student went to study a local pond. In one part of the pond she noticed tadpoles scraping at some pond weed. In another part she saw a water beetle holding a tadpole in its jaws.
(a) Construct a food chain for the pond.
(b) How many links are there in this chain?

Answer:

(a) Weed Tadpole Water beetle
(b) There are three links in this food chain.

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Question 35:

Construct (a) a long food chain, and (b) a short foodchain, ending with man.

Answer:

(a) Phytoplankton (algae) Zooplankton (protozoa) Small fish Big fish Man

(b) Plants Man

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Question 36:

(a) State one advantage of using jute bags over plastic bags for shopping.
(b) Write a common food chain of a pond ecosystem having four links.

Answer:

(a) Jute bags are biodegradable, and hence they are degraded by micro-organisms. Plastic bags are non-biodegradable, and hence they are not degraded by micro-organisms. Therefore, the advantage of using jute bags over plastic bags is that jute bags are environment friendly.

(b) Algae Protozoa Small fish Big fish

Page No 227:

Question 37:

We do not clean ponds or lakes but an aquarium needs to be cleaned periodically. Why?

Answer:

Ponds and lakes contain decomposers, which act as cleansing agents, whereas an aquarium does not have decomposers that cleanse it. Hence, an aquarium needs to be cleaned periodically.

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Question 38:

What will be the consequence of the absence of decomposers in the ecosystem?

Answer:

Decomposers help in decomposing dead plants and animals, and hence act as cleansing agents of the environment. They also help restore to the soil, air and water the various elements that plants and animals are made of, for reuse by the producers. If there were no decomposers in the ecosystem, then dead plants and animals would remain as such, and their elements would never be returned to the soil, air and water.

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Question 39:

Give two differences between food chain and food web.

Answer:

Food chain Food web
The sequence of living organisms in a community in which one organism consumes another for the transfer of food energy is called a food chain. The inter-connected food chains operating in an ecosystem, which establish relationships among various species, make up a food web.
It represents a unidirectional flow of energy. It represents the numerous pathways along which food energy flows.

Page No 227:

Question 40:

Write one or two words for each of the following statements/definitions :
(a) Each level of food chain where transfer of energy takes place
(b) The physical factors like temperature, rainfall, light soil air and water of an ecosystem
(c) Organisms which depend on the producers for food either directly or indirectly
(d) The physical and biological world where we live in
(e) Selfcontained unit of living things and their non-living environment needing only sunlight for its functioning

Answer:

(a) Trophic level
(b) Abiotic components
(c) Consumers
(d) Environment
(e) Ecosystem

Page No 227:

Question 41:

(a) What is meant by biodegradable waste materials? Give two examples of biodegradable wastes.
(b) Which of the following materials are non-biodegradable?
Aluminium wire, Tea leaves, Synthetic fibre, Wool

Answer:

(a) Waste materials that can be broken down into non-poisonous substances in nature in due course of time, by the action of micro-organisms such as certain bacteria, are called biodegradable wastes. Examples are paper and vegetable peels.

(b) Aluminium wire and synthetic fibre are non-biodegradable.

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Question 42:

(a) What is meant by non-biodegradable waste materials? Give two examples of non-biodegradable wastes.
(b) Which of the following materials are biodegradable?
Animal bones, Iron nails, Plastic mugs, Leather belts, Silver foil

Answer:

(a) Waste materials that cannot be broken down into non-poisonous or harmless substances in nature are called non- biodegradable wastes. Examples are plastic and iron nails.

(b) Animal bones and leather belts are biodegradable wastes.



Page No 228:

Question 43:

(a) Define an ecosystem. Give examples of any two ecosystems.
(b) List the biotic and abiotic components of an ecosystem.

Answer:

(a) An ecosystem is a self-sustained unit of living things (plants, animals and decomposers) and their non-living environment (air, water and soil).
Examples: A pond is an ecosystem that includes the aquatic life (aquatic animals and plants) that live in the pond water.
A forest is an example of a terrestrial ecosystem that includes the physical environment of the forest along with the plants and animals that live in that forest.

(b) The biotic components of an ecosystem are the plants, animals and decomposers present in it.
The abiotic components of an ecosystem are air, water and soil. The abiotic components also include physical factors such as light, temperature, pressure and humidity. Inorganic substances such as carbon dioxide, oxygen, water, nitrogen, sulphur and phosphorus are also abiotic components of an ecosystem.

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Question 44:

(a) What is a food chain? Give one example of a simple food chain.
(b) What is a 'food web'? Show its formation.

Answer:

(a) The sequence of living organisms in a community in which one organism consumes another organism to transfer food energy is called a food chain. An example of a simple food chain is that operating in a grassland:

                                   Grass                Deer                  Lion
                              (Producer)           (Herbivore)            (Carnivore)

(b) The inter-connected food chains operating in an ecosystem that establish a network of relationships among various species comprise a food web.
A food web is formed by many food chains operating together. A food web operating in a grassland is shown in the figure.

Five food chains are possible in this food web, which are as follows.


1) Grass Grasshopper Frog Hawk

2) Grass Grasshopper  Rat Fox

3) Grass Rabbit Fox

4) Grass Rat Snake Hawk

5) Grass Rat Hawk

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Question 45:

(a) What is meant by 'environment'?
(b) What type of substances are the major pollutants of the environment? Name two such substances.
(c) Name the organisms whose uncontrolled activities are damaging the environment.
(d) Explain why, it is better to use paper bags than plastic bags.

Answer:

(a) Our physical surroundings, which include the air, water bodies, the soil and all living organisms such as plants, animals, human beings and micro-organisms, constitute our environment.

(b) Non-biodegradable substances are the major pollutants of the environment. Two such substances are plastic articles and glass articles.

(c) Human beings are the organisms whose uncontrolled activities are damaging the environment.

(d) It is better to use paper bags than plastic bags because paper bags are biodegradable and can easily be degraded by micro-organisms, whereas plastic bags are non-biodegradable and cannot be degraded by micro-organisms.

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Question 46:

Which of the following constitutes a food chain?
(a) Grass, Wheat and Mango
(b) Grass, Goat and Human
(c) Goat, Cow and Elephant
(d) Grass, Fish and Goat

Answer:

(b) Grass, goat and human

Grass is eaten by goats, and goats are eaten by humans.

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Question 47:

In a food chain, the initial organism is usually :
(a) photosynthetic
(b) herbivore
(c) saprophytic
(d) parasitic

Answer:

(a) photosynthetic

The initial organism of a food chain is the producer, which produces food through photosynthesis.

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Question 48:

Which of the following represents a possible food chain found in a pond :

Primary
producers
Primary consumers Secondary
consumers
(a) green algae fish mosquito larvae
(b) fish green algae mosquito larvae
(c) mosquito larvae fish green algae
(d) green algae mosquito larvae fish

Answer:

(d) green algae, mosquito larvae, fish

In a pond, green algae are the primary producers. Green algae are consumed by mosquito larvae, which therefore become the primary consumers. Mosquito larvae are consumed by fish, which then become the secondary consumers.

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Question 49:

Which of the following are decomposers of dead organisms?

Bacteria Fungi Viruses
(a) no yes yes
(b) yes no yes
(c) yes yes no
(d) yes yes yes

Answer:

(c) yes, yes, no

Bacteria and fungi are decomposers of dead organisms.

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Question 50:

Which of the following is an artificial ecosystem?
(a) pond
(b) crop field
(c) lake
(d) forest

Answer:

(b) Crop field

A crop field is an artificial ecosystem, because it is made by man.

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Question 51:

Disposable plastic plates should not be used because :
(a) they are made of light weight materials
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials

Answer:

(d) they are made of non-biodegradable materials

Disposable plastic plates cannot be degraded by micro-organisms and hence should not be used. They will remain as such in the environment and pollute it.

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Question 52:

In a food chain, the third trophic level is always occupied by :
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers

Answer:

(a) carnivores

The third trophic level is always occupied by carnivores. The first trophic level is occupied by producers, the second by herbivores and the fourth by decomposers.

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Question 53:

Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as :
(a) eutrophication
(b) pollution
(c) biomagnification
(d) accumulation

Answer:

(c) biomagnification

The accumulation of non-biodegradable pesticides in the food chain in an increasing amount at each higher trophic level is known as biomagnification.

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Question 54:

If a grasshopper is eaten by a frog, 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 tertiary consumer

Answer:

(c) primary consumer to secondary consumer

A grasshopper eats grass; hence, the grasshopper is the primary consumer. A frog eats the grasshopper, so the frog becomes the secondary consumer. The energy transfer is from the primary consumer to the secondary consumer, i.e., from the grasshopper to the frog.

Page No 228:

Question 55:

An ecosystem includes :
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) all living organisms and input of sun's energy

Answer:

 (c) both living organisms and non-living objects

Both living organisms and non-living objects are components of an ecosystem.

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Question 56:

The decomposers in an ecosystem :
(a) convert inorganic material to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic material into organic compounds
(d) do not break down organic compounds

Answer:

(b) convert organic materials to inorganic forms

Decomposers convert the organic matter present in the bodies of dead organisms into inorganic forms and mix them with the soil.



Page No 229:

Question 57:

What will happen if deer is missing in the food chain given below?
Grass → Deer → Tiger
(a) The population of tigers increases
(b) the population of grass decreases
(c) Tigers will start eating grass
(d) The population of tigers decreases and the population of grass increases.

Answer:

(d) The population of tigers decreases and the density of grass increases.

If deer are removed from the given food chain, the population of tigers will decrease as they will not have deer for their food and will starve to death. The density of grass will increase as there is no organism to consume it as food.

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Question 58:

Organisms which synthesise carbohydrates from inorganic compounds by using radiant energy are called :
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores

Answer:

(b) producers

Green plants are producers that prepare carbohydrates as food from inorganic compounds, such as carbon dioxide and water, by using sunlight as the radiant energy.

Page No 229:

Question 59:

Organisms of a higher trophic level which feed on several types of organisms belonging to a number of lower trophic levels constitute the :
(a) ecosystem
(b) food web
(c) ecological pyramid
(d) food chain

Answer:

(b) food web

Organisms of a higher trophic level that feed on several types of organisms belonging to a number of lower trophic levels constitute a food web.

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Question 60:

In the following groups of materials, which group/groups contain only non-biodegradable materials?
(i) wood, paper, leather
(ii) polythene, detergent, PVC
(iii) plastic, detergent, grass
(iv) plastic, bakelite, DDT

(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)

Answer:

(d) (ii) and (iv)

These materials cannot be degraded by micro-organisms and hence are non-biodegradable.

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Question 61:

Which of the following statement is incorrect?
(a) all green plants and blue green algae are producers
(b) green plants get their food from readymade organic compounds
(c) producers prepare their own food from inorganic compounds
(d) plants convert solar energy into chemical energy

Answer:

(b) Green plants get their food from readymade organic compounds.

This is an incorrect statement as green plants prepare their food themselves; they do not get readymade organic compounds as their food.

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Question 62:

Which of the following group of organisms are not constituents of a food chain?
(i) grass, lion, rabbit, wolf
(ii) plankton, man, fish, grasshopper
(iii) wolf, grass, snake, tiger
(iv) frog, snake, eagle, grass, grasshopper

(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iv)

Answer:

(c) (ii) and (iii)

A food chain is a sequence of living organisms in a community or ecosystem, in which one organism is consumed the other. The organisms given in options (i) and (iii) cannot comprise a food chain.

Page No 229:

Question 63:

In the figure given alongside, the various trophic levels are shown in the form of a pyramid. At which trophic level the maximum energy is available?
(a) T4
(b) T2
(c) T1
(d) T3
Figure

Answer:

(c) T1

At T1, producers, which make food, are present, and hence they are at the bottom of the trophic levels. As they get energy directly from the sun, they have the maximum energy. This energy keeps on reducing as it is passed on to the next trophic levels.

Page No 229:

Question 64:

One of the following is not a biodegradable material. This one is :
(a) cotton
(b) animal bones
(c) aluminium foil
(d) wood

Answer:

(c) aluminium foil

Aluminium foil cannot be degraded by the action of micro-organisms and hence is non-biodegradable.

Page No 229:

Question 65:

Which of the following is not a non-biodegradable material?
(a) nylon socks
(b) plastic school bag
(c) jute carry bag
(d) polyester clothes

Answer:

(c) jute carry bag

A jute carry bag is made from jute, which is a plant fibre. Hence, it is biodegradable.

Page No 229:

Question 66:

The use of one of the following will pollute the environment. This one is :
(a) paper carry bags
(b) cotton cloth carry bags
(c) nylon cloth carry bags
(d) jute carry bags

Answer:

(c) nylon cloth carry bags

Nylon cloth is non-biodegradable and pollutes the environment.

Page No 229:

Question 67:

One of the following is not a consumer. This one is :
(a) giraffe
(b) antelope
(c) algae
(d) alligator

Answer:

(c) algae

Algae are producers, which prepare their food themselves through photosynthesis. They are not consumers.

Page No 229:

Question 68:

Which of the following is not a producer?
(a) grass
(b) zooplankton
(c) phytoplankton
(d) paddy

Answer:

(b) zooplankton

Zooplankton are herbivorous micro-organisms such as protozoa that are found in water bodies. They depend upon producers for food and hence are not producers.

Page No 229:

Question 69:

One of the following is a micro-consumer. This one is :
(a) ant
(b) lice
(c) fungi
(d) mosquito

Answer:

(c) fungi

Fungi are micro-consumers, which consume micro-producers.

Page No 229:

Question 70:

Which of the following act as decomposers in an ecosystem?
(a) Lactobacillus bacteria
(b) Cyanobacteria
(c) Putrefying bacteria
(d) Rhizobium bacteria

Answer:

(c) Putrefying bacteria

Putrefying bacteria decompose dead organisms, and hence act as decomposers in an ecosystem.

Page No 229:

Question 71:

One of the following helps in the recycling of materials in an ecosystem. This one is :
(a) autotrophs
(b) saprotrophs
(c) omnivores
(d) carnivores

Answer:

(b) saprotrophs

Saprotrophs such as bacteria and fungi recycle the organic matter present in the bodies of dead organisms by mixing it with the soil.

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Question 72:

In the food chain comprising of a snake, grass, insect, and frog, the secondary consumer is :
(a) insect
(b) snake
(c) frog
(d) grass

Answer:

(c) frog

The grass is eaten by the insect, which is eaten by the frog, which is eaten by the snake. Hence, the grass is the producer, the insect is the primary consumer, the frog is the secondary consumer and the snake is the tertiary consumer.

Page No 229:

Question 73:

Sahara Desert was formed over a period of time due to one of the following uncontrolled activities of man :
(a) excessive cutting down of forest plants and trees
(b) excessive killing of large herbivores
(c) excessive killing of large carnivores
(d) excessive use of poisonous chemicals herbicides

Answer:

(c) excessive killing of large carnivores

Excessive killing of lions resulted in an increase in the number of herbivores, which in turn consumed all the vegetation. Hence, the Sahara Desert was formed.



Page No 230:

Question 74:

The sea water contains water beetles, tadpole, fish and weeds.
(a) Write a food chain comprising all the given organisms.
(b) Which organisms in the food chain are (i) herbivore, and (ii) carnivores?
(c) Which organisms are (i) predators, and (ii) prey?
(d) Which organisms can trap solar energy to make food?
(e) Which organism is a secondary consumer?

Answer:

(a) Weeds Tadpole Water beetle Fish

(b) (i) The tadpole is a herbivore, and (ii) the water beetle and the fish are carnivores.

(c) (i) The water beetle and the fish are predators, and (ii) the tadpole and the water beetle are prey.

(d) Weeds can trap solar energy to make food.

(e) The water beetle is the secondary consumer in the given food chain.

Page No 230:

Question 75:

The following is a food chain that ends with human :
plants → bee → human
(a) Explain how plants provide food for bees.
(b) How do bees provide food for humans?
(c) How does this food chain differ form a usual food chain involving human such as : plants → goat → human?
(d) Do you think that the food chain given in this question can really be regarded as a food chain? Explain your answer.

Answer:

(a) The nectar present in the flowers of plants serves as food for bees. Bees suck nectar from flowers.

(b) Humans obtain honey made by bees and consume it as food.

(c) This food chain differs from an usual one, as humans, here, consume honey made by bees, whereas, usually, the food chain resembles Plants Goats Humans, in which humans consume the meat of goats directly.

(d) No, it cannot be regarded as a food chain, as humans do not consume bees directly but only consume the food made by them.

Page No 230:

Question 76:

A food chain occurring in the sea which provides food for many people can be written as :
phytoplankton → zooplankton → X → Y
(a) Name one phytoplankton.
(b) Name two zooplanktons.
(c) What could be X?
(d) Name the organism which Y could be.
(e) Which organism in the above food chain is a (i) primary consumer, and (ii) tertiary consumer?

Answer:

(a) Algae are phytoplankton.

(b) Jelly fish and copepods are examples of zooplankton.

(c) X is a small fish.

(d) Y could be a big fish.

(e) (i) Zooplankton are primary consumers, and (ii) big fish are tertiary consumers.

Page No 230:

Question 77:

Some hunters are roaming in the plush green forest of Africa. They spot a deer and kill it. They decide to roast the deer there and then and eat it. When the hunters had just finished enjoying the feast of roasted deer, a lion attacks them. The lion kills one of the hunters and eats his flesh.
(a) write a food chain which provides food to lion in this case.
(b) Which animal (other than deer) the lion could look for food if he did not get the hunter as prey?
(c) Which other animal in the forest could have been in place of lion?
(d) How does the above food chain differ form the food chain such as : plants → goat → man?
Figure

Answer:

(a) The following is the food chain that provides food to the lion in the given case:
                                 Plants Deer Man Lion

(b) The lion could have looked for a herbivore, such a wild buffalo or a zebra, if it he had not got the hunter as prey.

(c) Any top consumer, such as a tiger or a python, could have been in the place of the lion in the forest.

(d) In the food chain, 
Plants Goat Man
man is the top consumer whereas, in the food chain,

Plants Deer Man Lion,
the top consumer is lion.

Page No 230:

Question 78:

What would happen to the number of rabbits and grass plants if the number of foxes :
(a) increased?
(b) decreased?

Answer:

(a) If the number of foxes increases, it will lead to foxes consuming more rabbits as food, which will lead to a decrease in the number of rabbits. Hence, grass plants will grow denser as there will be fewer rabbits to consume them.

(b) If the number of foxes decreases, then there will be fewer foxes to consume rabbits as food, so the number of rabbits will increase, which will in turn lead to rabbits consuming more grass plants as food. Hence, grass plants will become sparser.

Page No 230:

Question 79:

What would happen to the number of grass plants and foxes if the number of rabbits :
(a) increased?
(b) decreased?

Answer:

(a) If the number of rabbits increases, it will lead to rabbits consuming more grass plants, and hence grass plants will become sparser. As foxes consume rabbits, any increase in the number of rabbits will lead to an increase in the number of foxes.

(b) If the number of rabbits decreases, then there will be less food for foxes. Hence, they will not be able to survive, because of the shortage of food, and their number will decrease. A decrease in the number of rabbits will lead to an increase in the density of grass plants, as there will be fewer rabbits to consume them.



Page No 231:

Question 80:

(a) Match the terms given in column I with the terms given in column II and column III having the same meaning :

Column I Column II Column III
(i) Secondary consumer Herbivore 1st trophic level
(ii) Primary consumer Autotroph 3rd trophic level
(iii) Producer Carnivore 4th trophic level
(iv) Tertiary consumer Large carnivore 2nd trophic level
(b) Give one example of a food chain having four organisms. Below each organism write the three appropriate terms from the part (a) above which you think it represents.

Answer:

Column I Column II Column III
(i) Secondary consumer Carnivore 3rd trophic level
(ii) Primary consumer Herbivore 2nd trophic level
(iii) Producer Autotroph 1st trophic level
(iv) Tertiary consumer Large carnivore 4th trophic level

(b)         Grass           Grasshopper                Frog                           Bird
         Producer         Primary consumer      Secondary consumer     Tertiary consumer
          Autotroph             Herbivore                  Carnivore                    Large carnivore
    1st trophic level     2nd trophic level         3rd trophic level            4th trophic level



Page No 240:

Question 1:

What percentage of the solar energy is trapped and utilised by the plants?

Answer:

One per cent of solar energy is trapped and utilised by plants.

Page No 240:

Question 2:

What percentage of energy available at the producer level is transferred at successive trophic levels in a food chain?

Answer:

Ten per cent of the energy available at the producer level is transferred at successive trophic levels in a food chain.

Page No 240:

Question 3:

Name the process in which a harmful chemical enters the food chain and gets concentrated at each trophic level.

Answer:

Biomagnification is the process by which a harmful chemical enters the food chain and gets concentrated at each trophic level.

Page No 240:

Question 4:

In a food chain consisting of grass, frog, bird and insects, where will the concentration of the harmful chemicals be maximum?

Answer:

The bird in the food chain will have the maximum concentration of harmful chemicals among the given organisms, because it lies at the highest trophic level.

Page No 240:

Question 5:

If a harmful chemical enters a food chain comprising cat, mice and plants, which one of these organisms is likely to have the maximum concentration of the harmful chemical in its body?

Answer:

The cat in the food chain will have the maximum concentration of harmful chemicals in its body because it lies at the highest trophic level.

Page No 240:

Question 6:

Which radiations are absorbed by ozone layer?

Answer:

Ultraviolet radiations are absorbed by the ozone layer.

Page No 240:

Question 7:

Name the group of chemical compounds which damages the ozone layer.

Answer:

The group of chemical compounds that damages the ozone layer is known as chlorofluorocarbons (CFCs).

Page No 240:

Question 8:

Name two waste materials which can be recycled.

Answer:

Paper and plastic are two waste materials that can be recycled.

Page No 240:

Question 9:

Name the process by which the volume of solid wastes can be reduced.

Answer:

Landfill is the process by which the volume of solid wastes can be reduced.

Page No 240:

Question 10:

If 5 joules of energy is available at producer level (plants), then how much energy will be transferred to the lion in the following food chain?
Plants → Goat → Lion

Answer:

The energy that will be transferred to the lion in the given food chain is 0.05 J.

Page No 240:

Question 11:

State whether the following statement is true or false :
Only 10 per cent of the light energy given by the sun is available for transfer at each higher trophic level in a food chain.

Answer:

False. Only one per cent of light energy is trapped by plants, and of this, only 10 per cent is transferred at each trophic level in a food chain.

Page No 240:

Question 12:

Where does all the energy in living organisms originate from?

Answer:

All the energy in living organisms originates from the sun.

Page No 240:

Question 13:

Why are there rarely more than five links (or five organisms) in a food chain?

Answer:

There are rarely more than five links (or five organisms) in a food chain because, according to the 10 per cent law, only 10 per cent of the available energy is transferred to the next trophic level. So, at the higher trophic levels, the amount of energy is reduced to such an extent that it becomes insufficient for an organism to sustain itself.

Page No 240:

Question 14:

Name two predators of snakes in a food web operating in a forest ecosystem.

Answer:

Hawks and peacocks are two predators of snakes in a food web operating in a forest ecosystem.

Page No 240:

Question 15:

Fill in the following blanks with suitable words :
(a) Ultraviolet rays can cause skin..............
(b) Pesticides enter the food chain at the ...........level
(c) Grass → ........... → Human
(d) Lettuce → ............. → Fox
(e) Plants → Antelope → ............

Answer:

(a) Ultraviolet rays can cause skin cancer.
(b) Pesticides enter the food chain at the producer level.
(c) Grass → Goat → Human
(d) Lettuce → Rabbit → Fox
(e) Plants → Antelope → Lion



Page No 241:

Question 16:

What is ten per cent law? Explain with an example.

Answer:

According to the 10 per cent law, only 10 per cent of the energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.
In the following food chain, only 10 per cent of energy is transferred to the next trophic level. The flow of energy is shown below.
                 Plants       Grasshopper      Frog          Snake       Hawk
               100,000 J            10,000 J               1,000 J               100 J             10 J
When the energy available at the producer level is 100,000 J, only 10 J of energy is available to the hawk.

Page No 241:

Question 17:

Write the full form of CFC. Give its one harmful effect.

Answer:

The full form of CFC is chlorofluorocarbon.
Chlorofluorocarbons react with the ozone in the upper atmosphere and destroy the ozone layer, making the layer thinner and allowing ultraviolet (UV) radiation to pass through it and fall on the earth's surface. This UV radiation can cause skin cancer and other ailments in humans and also affect plants and animals.

Page No 241:

Question 18:

Explain how, harmful ultraviolet radiations of sunlight are prevented from reaching the earth's surface.

Answer:

Harmful radiations of sunlight are prevented from reaching the earth's surface by the ozone layer in the upper atmosphere, which absorbs them.

Page No 241:

Question 19:

What are the causes of depletion of ozone layer? Which diseases are likely to be caused if the ozone layer will become thinner?

Answer:

Chlorofluorocarbons, which are widely used in refrigerators, fire extinguishers and aerosol sprayers, are released into the air and react with the ozone present in the ozone layer and destroy it gradually. This causes the depletion of the ozone layer. If the ozone layer becomes thinner, harmful ultraviolet radiations will enter the earth and may cause skin cancer and other ailments in humans and also affect plants and animals.

Page No 241:

Question 20:

Explain how harmful chemicals enter our bodies.

Answer:

Chemical substances such as pesticides are sprayed over crop plants to protect them from pests and diseases. When herbivorous animals eat plant food, these poisonous chemical pesticides go into their bodies. Man, being an omnivore, eats plant food as well as the flesh of herbivores. Thus, the pesticides present in plant food and in the bodies of herbivores are transferred to the bodies of humans through food. In this way, harmful chemicals enter our bodies.
 

Page No 241:

Question 21:

'If we excessively use pesticides to protect the crops from diseases, then it may cause long-term  damage to mankind'. Justify this statement.

Answer:

Chemical substances such as pesticides are sprayed over crop plants to protect them from pests and diseases. When herbivorous animals eat the plant food, these poisonous chemical pesticides go into their bodies. Man, being an omnivore, eats plant food as well as the meat of herbivores. Thus, the pesticides present in plant food and herbivores get transferred to man's body through food. Pesticides are non-biodegradable chemicals, so they get accumulated at each trophic level. Since humans occupy the top level in any food chain, the maximum amount of harmful chemical pesticides gets accumulated in our bodies, damaging our health gradually.
Hence the statement 'excessive use of pesticides to protect crops from diseases may cause long-term damage to mankind' is justified.

Page No 241:

Question 22:

What is meant by biological magnification? With the help of a food chain, explain how biological magnification of harmful chemicals can occur.

Answer:

The increase in the concentration of harmful substances, such as pesticides, in the body of living organisms at each level of a food chain is called biological magnification.
Chemical substances such as pesticides are sprayed over crop plants to protect them from pests and diseases. When herbivorous animals eat plant food, these poisonous chemical pesticides go into their bodies. Man, being an omnivore, eats plant food as well as the meat of herbivores. Thus, the pesticides present in plant food and herbivores get transferred to man's body through food. Pesticides are non-biodegradable chemicals, so they get accumulated at each trophic level. Since humans occupy the top level in any food chain, the maximum amount of harmful chemical pesticides gets accumulated in our bodies, damaging our health gradually.
The following food chain explains how biological magnification of harmful chemicals can occur.                                                        Plants Herbivore Man

Page No 241:

Question 23:

What is meant by bioconcentration of pesticides? Which common pesticide has accumulated in human body in considerable amounts?

Answer:

The increase in the concentration of harmful chemical substances, such as pesticides, in the body of living organisms at each trophic level of a food chain is called bioconcentration of pesticides.
The common pesticide that has accumulated in the human body in considerable amounts is DDT.

Page No 241:

Question 24:

What is garbage? What does garbage consist of?

Answer:

Household waste or rubbish is called garbage. Garbage consists of leftover food, fruit, vegetable peels, fallen leaves of potted plants, waste paper, unwanted plastic objects, glass articles, metal objects, old wooden objects, rags, discarded shoes, sewage, etc.

Page No 241:

Question 25:

Name the various modes of waste disposal.

Answer:

The various modes of waste disposal are as follows.
1) Recycling
2) Preparation of compost
3) Incineration
4) Landfill
5) Sewage treatment

Page No 241:

Question 26:

How can the wastes such as paper, plastic and metal objects be disposed of?

Answer:

Wastes such as paper, plastic and metal objects can be disposed of through recycling. This is done in the following ways.

1) Waste paper is sent to paper mills, where it is reprocessed to make new paper once again.
2) Broken plastic articles, such as plastic bags, buckets, bowls, cups and plates, are sent to plastic-processing factories, where they are melted and remoulded to make new articles.
3) Waste metal articles are sent to metal industries, where they are melted into solid metal and recycled for various purposes.

 

Page No 241:

Question 27:

Give a method for the disposal of household wastes such as left-over food, fruit and vegetable peels, and leaves of potted plants.

Answer:

Leftover food, fruit and vegetable peels, and leaves of potted plants can be converted into compost by burying them in a pit dug in the ground. The compost thus prepared can be used as manure. In this way, household wastes can be disposed of.

Page No 241:

Question 28:

What is meant by incineration? for what purpose is it used?

Answer:

Incineration means reducing something to ashes. In this method, waste material is burnt and converted to ashes. It is used to destroy household waste, chemical waste and biological waste (hospital waste).

Page No 241:

Question 29:

How are most of the solid wastes in urban areas disposed of?

Answer:

Most of the solid wastes in urban areas are disposed of by dumping them in low-lying sites. These sites are then covered with earth to level the uneven ground. This process is called landfill.

Page No 241:

Question 30:

State two advantages of using disposable paper cups over disposable plastic cups.

Answer:

Two advantages of using disposable paper cups over disposable plastic cups are as follows.
(a) Disposable paper cups decay naturally and become harmless after some time, but disposable plastic cups do not.
(b) Disposable paper cups usually do not pollute the environment, but disposable plastic cups pollute the environment.

Page No 241:

Question 31:

What is sewage? How is sewage disposed of?

Answer:

The dirty drain water containing urine and faeces that is carried from our homes by underground pipes (called sewers) is called sewage. It is disposed of by treating it at a sewage treatment plant.

Page No 241:

Question 32:

Write the harmful effects of ozone depletion.

Answer:

The following are the harmful effects of ozone depletion.
1) It can lead to skin cancer in humans.
2) It can lead to cataract in humans.
3) It can lead to damage to our immune system by lowering the body's resistance to diseases.
4) It can lead to many diseases in animals.
5) It can lead to damage to plants.

Page No 241:

Question 33:

What would happen if the ozone layer in the atmosphere completely disappears?

Answer:

If the ozone layer in the atmosphere completely disappears, then the harmful ultraviolet radiations from the sun would enter the earth's surface and cause skin cancer and many other ailments in humans and animals, and may also damage plants.

Page No 241:

Question 34:

(a) With the help of a flow diagram, describe how energy from the sun flows through various trophic levels.
(b) Explain why, the flow of energy in the ecosystem is said to be unidirectional.

Answer:

(a) Energy from the sun flows through various trophic levels in the following steps.
1) Green plants trap solar energy with the help of their green pigment, chlorophyll, and convert it into chemical energy. They store this energy in the form of carbohydrates. On an average, about one per cent of the sun's energy falling on the leaves of green plants is used by the plants in the process of photosynthesis and stored as the chemical energy of food.
2) When plants are eaten by herbivores, the chemical energy stored in the plants is transferred to them.
3) The herbivores are then consumed by carnivores, and the chemical energy stored in the flesh of the herbivores is transferred to the carnivores.
4) Some of the energy from producers and consumers is also utilised for the life processes of micro-organisms called decomposers. Decomposers, in turn, release the unutilised energy into the environment as heat. The energy that is not utilised by producers, consumers and decomposers is lost in the environment as heat. This heat is called community heat.

(b) Energy enters plants from the sun during food production through photosynthesis. This energy is then passed on from one organism to another in a food chain. The energy given out by organisms as heat is lost in the environment and does not return to be used by plants again. This makes the flow of energy in an ecosystem unidirectional. Thus, the flow of energy in an ecosystem is said to be unidirectional because the energy lost as heat from the organisms in a food chain cannot be reused by plants in photosynthesis.
 

Page No 241:

Question 35:

(a) What is ozone? How is it formed?
(b) How does ozone layer protect us from harmful effects in the environment?
(c) What is UNEP? What step has been taken by UNEP in 1987 to prevent too much damage to the ozone layer?

Answer:

(a) Ozone is made up of three atoms of oxygen combined together. It is formed high up in the atmosphere by the action of ultraviolet (UV) radiation on oxygen gas. The UV radiation from the sun splits the oxygen gas into free oxygen atoms.
    O2                O             +           O           +         O
Oxygen         (UV radiation          Oxygen               Oxygen
molecule        from the sun)           atom                    atom

An oxygen atom reacts with an oxygen molecule to form an ozone molecule.

    O2          +       O               O3
 Oxygen          Oxygen             Ozone  
molecule           atom            molecule

(b) The ozone layer protects us from the harmful effects of the UV radiation from the sun by absorbing it and preventing it from reaching the earth's surface.

(c) The UNEP is United Nations Environment Programme. In 1987, in an attempt to protect the ozone layer, the UNEP forged an agreement among its member countries to freeze the production of chlorofluorocarbons at 1986 levels.

Page No 241:

Question 36:

(a) How is energy introduced into the ecosystem?
(b) Consider the following food chain :
(i) Plants → Mice → Snakes → Hawks
(ii) Plants → Mice →Hawks
If energy available at the producer level in both the food chains is 100 J, in which case will hawks get more energy as food and by how much? Justify your answer.

Answer:

(a) Plants trap solar energy to make their food. In this way, energy is introduced into the ecosystem by the sun.

(b) According to the 10 per cent law, only 10 per cent of the energy entering a particular trophic level of organisms is available for the next higher trophic level. If the energy at the producer level is 100 J, the energy at the hawk level in both the food chains can be calculated as under.
 (i) Plants    Mice   Snakes Hawks
        100 J    10 J        1 J          0.1 J

(ii) Plants Mice Hawks
      100 J      10 J    1 J

So, it is clear that hawks will get 10 per cent more energy in the second food chain compared with the first food chain.          

Page No 241:

Question 37:

(a) Explain why, a food chain usually cannot have more than three or four steps.
(b) Calculate the amount of energy that will be available to big fish in the following food chain, if 10,000 J of energy is available to small algae from the sun :
Small algae → Zooplankton → Fish → Big fish

Answer:

(a) At each trophic level in a food chain, a large portion of the energy available is utilised for the maintenance of organisms in that trophic level and is lost as heat. Food chains usually cannot have more than three or four steps because the energy available for organisms in any additional step will be so small that it will be insufficient to sustain the life of those organisms.

(b) The amount of energy available to big fish will be 1 J. It can be calculated as follows-

Sun          Small algae        Zooplankton    Fish    Big fish
 10000 J         1000 J                   100 J          10 J        1 J

Page No 241:

Question 38:

(a) Name and state the law given by Lindeman which tells us how much energy entering a particular trophic level of organisms is available for trasnsfer to the next higher trophic level.
(b) How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 10,000 J of energy is available to paddy from the sun?

Answer:

(a) The law given by Lindeman is called the 10 per cent law. It states that only 10 per cent of the energy entering a particular trophic level of organisms is available for transfer to the next trophic level.

(b) Ten per cent of the energy will be available to hawks.
In this food chain, the energy transfer will take place as follows.
 Sun            Paddy      Mice       Snakes      Hawks
10,000 J        1,000 J         100 J             10 J                1 J



Page No 242:

Question 39:

What provides the energy which then flows through a food chain?
(a) glucose
(b) oxygen
(c) respiration
(d) sunlight

Answer:

(d) Sunlight

Sunlight provides energy to plants for preparing food, and this energy is then passed on to the next trophic levels through a food chain.

Page No 242:

Question 40:

Which pollutant released into the air during refrigeration and airconditioning is the greatest contributor to the depletion of ozone layer?
(a) BHC
(b) DDT
(c) CFC
(d) UNEP

Answer:

(c) CFC

Chlorofluorocarbons (CFCs) are released into the air during refrigeration and air conditioning and are the greatest contributor to the depletion of the ozone layer.

Page No 242:

Question 41:

In the food chain given below, if the amount of energy available at fourth trophic level is 5 kJ, what was the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 500 kJ
(b) 50 kJ
(c) 5000 kJ
(d) 5 kJ

Answer:

(c) 5,000 kJ

According to the 10 per cent law, only 10 per cent of the energy available in a trophic level is passed on to the next level. Hence, if the amount of energy available at the fourth trophic level is 5 kJ, the energy available at the producer level will be 5,000 kJ: 5 → 50 → 500 → 5,000.

Page No 242:

Question 42:

Which of the following limits the number of trophic levels in a food chain?
(a) insufficient food supply from producer level
(b) decrease in energy at higher trophic levels
(c) increase in the number of organisms at higher trophic levels
(d) accumulation of harmful chemicals at higher trophic levels

Answer:

(b) Decrease in energy at higher trophic levels

According to the 10 per cent law, the amount of energy decreases in each trophic level, and hence the number of trophic levels in a food chain is limited.

Page No 242:

Question 43:

What percentage of sun's energy falling on the leaves of green plants is utilised by the plants in the process of photosynthesis and stored as chemical energy of food?
(a) 99 per cent
(b) 10 per cent
(c) 1 per cent
(d) 20 per cent

Answer:

(c) 1 per cent
Only one per cent of the sun's energy falling on the leaves of green plants is utilised by the plants in the process of photosynthesis and stored as the chemical energy of food.

Page No 242:

Question 44:

The depletion of ozone layer in the upper atmosphere is mainly due to the emission of :
(a) unburnt hydrocarbons
(b) chlorofluorocarbons
(c) greenhouse gases
(d) ultraviolet radiations

Answer:

(b) chlorofluorocarbons

Chlorofluorocarbons emitted by air-conditioners, refrigerators and jet planes cause the depletion of the ozone layer.

Page No 242:

Question 45:

In an ecosystem, the ten per cent energy available for transfer from one trophic level to the next is in the form of :
(a) heat energy
(b) light energy
(c) chemical energy
(d) mechanical energy

Answer:

(c) chemical energy

The food prepared by plants is in the form of chemical energy, which is passed on to the next trophic level in an ecosystem.

Page No 242:

Question 46:

The flow of energy in an ecosystem is always :
(a) unidirectional
(b) bidirectional
(c) cyclic
(d) multidirectional

Answer:

(a) unidirectional

Energy always flows in one direction in an ecosystem, from a lower trophic level to a higher trophic level.

Page No 242:

Question 47:

The excessive exposure of humans to ultraviolet rays results in :
(i) damage to immune system
(ii) damage to lungs
(iii) skin cancer
(iv) peptic ulcers

(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)

Answer:

(c) (i) and (iii)

Excessive exposure of humans to ultraviolet rays results in skin cancer and damage to the immune system.

Page No 242:

Question 48:

Which of the following gets the minimum energy through the food chain in an ecosystem?
(a) carnivore
(b) large carnivore
(c) producer
(d) herbivore

Answer:

(b) large carnivore

As large carnivores are at the upper trophic levels, they get the minimum energy through the food chain, according to the 10 per cent law.

Page No 242:

Question 49:

A food chain comprises of cat, seed-eating bird, plants, and dog. The organism which will have the maximum concentration of harmful pesticides coming through the food chain is most likely to be :
(a) cat
(b) plants
(c) dog
(d) seed-eating bird

Answer:

(c) dog

The concentration of harmful pesticides in the bodies of birds and animals increases at each trophic level, and hence the dog in the given food chain will have the maximum concentration of harmful pesticides. 

Page No 242:

Question 50:

An aquatic food chain comprises of the organisms like tadpoles, weeds, fish and water beetles. The organism which gets the minimum energy through this food chain is :
(a) water beetles
(b) tadpoles
(c) weeds
(d) fish

Answer:

(d) fish

As fish are in the top trophic level in an aquatic food chain, they get the minimum energy, according to the 10 per cent law.

Page No 242:

Question 51:

Most of the water surface of a lake is covered with algae. This algae is part of the food chain which also includes small fish, bird, larvae and big fish. Which of the following will obtain the maximum energy?
(a) big fish
(b) bird
(c) larvae
(d) small fish

Answer:

(c) larvae

Larvae feed on algae for their nutrition, so they get the energy they require directly from the producers. Thus, they get the maximum energy among all the consumers.

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Question 52:

If the energy available at the producer level in a food chain is 150 J, how much energy will be transferred to : tertiary consumer?
(a) 15 J
(b) 10 J
(c) 1.50 J
(d) 0.15 J

Answer:

(d) 0.15 J

According to the 10 per cent law, only 10 per cent of the energy available in one trophic level is transferred to the next trophic level.

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Question 53:

If the energy transferred to a tertiary consumer in a food chain is 10 J, how much energy was available to the primary consumer?
(a) 100 J
(b) 500 J
(c) 1000 J
(d) 5000 J

Answer:

(c) 1,000 J

According to the 10 per cent law, only 10 per cent of the energy available in one trophic level is transferred to the next trophic level.

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Question 54:

In addition to wheat plants, a crop field ecosystem has organisms such as snake, peacock, eagle and mice. If the wheat plants are sprayed with pesticides periodically, which of the following will have the minimum concentration of pesticides in the body?
(a) snake
(b) eagle
(c) mice
(d) peacock

Answer:

(c) mice

As mice are in the lowest trophic level, they will have the minimum concentration of pesticides in their body.



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Question 55:

Which of the following is the best method to dispose of biological wastes from hospitals?
(a) landfill
(b) recycling
(c) incineration
(d) composting

Answer:

(c) Incineration

Incineration, which means burning harmful wastes into ashes, is the best method to dispose of biological wastes from hospitals.

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Question 56:

In an ecosystem :
(i) the flow of energy is unidirectional
(ii) the flow of materials is unidirectional
(iii) the flow of materials is cyclic
(iv) the flow of energy is cyclic.

(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (i) and (iii)

Answer:

(d) (i) and (iii)

In an ecosystem, the flow of energy is unidirectional and the flow of materials is cyclic.

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Question 57:

The ten per cent law is associated with
(a) transfer of energy from various trophic levels to decomposers in a food chain
(b) transfer of ATP energy into muscular energy
(c) transfer of chemical energy from one organism to another
(d) transfer of sun's energy to the organisms called producers.

Answer:

(c) transfer of chemical energy from one organism to another

The 10 per cent law is associated with the transfer of chemical energy from one organism to another.

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Question 58:

The harmful chemical which is accumulating in human beings through food chain is :
(a) benzenehexachloride
(b) dichlorodiphenyltrichloroethane
(c) chlorofluorocarbon
(d) abscisic acid

Answer:

(b) dichlorodiphenyltrichloroethane

The harmful pesticide that accumulates in the bodies of human beings through the food chain, through a process known as biomagnification, is dichlorodiphenyltrichloroethane (DDT).

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Question 59:

O2 is converted into O3 by the action of :
(a) infrared radiations
(b) ultraviolet radiations
(c) gamma radiations
(d) cosmic radiations

Answer:

(b) ultraviolet radiations

Oxygen is converted into ozone by ultraviolet radiations.

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Question 60:

Which of the following cannot be added in a composting pit to prepare compost?
(a) sunflower plants
(b) fruit and vegetable peels
(c) flowers of plastic
(d) red worms

Answer:

(c) flowers of plastic

Plastic is a non-biodegradable substance, and hence it cannot be decomposed by composting.

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Question 61:

The gas A is used by most of the animals to obtain energy from food by the process of respiration. When A is acted upon by radiation X, it gets converted into another gas B which is an allotrope of A but poisonous when inhaled. B forms a kind of layer C in the upper atmosphere which absorbs radiations X coming from a source Y and prevent them from reaching the earth. Some chemicals Z released from the various devices on the earth are destroying the layer C slowly. In fact, a hole has already been formed in layer C over the area D of the earth.
(a) What are gases (i) A, and (ii) B? Write their molecular formulae.
(b) Name the layer C.
(c) What are (i) X, (ii) Y, and (iii) Z?
(d) Name the area D.
(e) Name any two human ailments which may be caused by X.

Answer:

(a) (i) A is oxygen (O2), and (ii) B is ozone (O3).

(b) C is the ozone layer.

(c) (i) X is ultraviolet (UV) radiations.
(ii) Y is the sun.
(iii) Z is chlorofluorocarbons (CFCs).

(d) D is Antarctica.

(e) Skin cancer and cataract are two human ailments that may be caused by X (ultraviolet radiations).

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Question 62:

The surface of water in a lake appears green due to a layer of tiny free-floating organisms X on its surface. The lake water also contains organisms like water beetle, fish and tadpole. The sun shines over the lake water and provides energy for the functioning of this lake ecosystem.
(a) What could organisms X be?
(b) Write a food chain comprising of all the four organisms mentioned.
(c) What is the general name of the food chains like the one written above?
(d) Name (i) secondary consumer (ii) producer (iii) tertiary consumer, and (iv) primary consumer, in the above food chain.
(e) If the tertiary consumer gets 0.2 J of energy from the secondary consumer, then how much energy was radiated by the sun to the producer?

Answer:

(a) X could be phytoplankton.

(b) Phytoplankton Tadpole Water beetle Fish

(c) 'Aquatic food chain' is the general name of food chains such as the one described above.

(d) (i) In the given food chain, the water beetle is the secondary consumer.
(ii) The phytoplankton is the producer.
(iii) The fish is the tertiary consumer.
(iv) The tadpole is the primary consumer.

(e) Sun Phytoplankton Tadpole Water beetle Fish
    20,000 J       200 J           20 J            2 J          0.2 J

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Question 63:

A forest ecosystem having a lot of green plants has some foxes, lions and rabbits in it.
(a) Write a food chain comprising all the four organisms mentioned above.
(b) Name (i) one herbivore, and (ii) two carnivores, in this food chain.
(c) Name the link which is a predator as well as a prey.
(d) Name (i) second trophic level, and (ii) third trophic level.
(e) Which link of this food chain can feed on second trophic level as well as third trophic level, independently?
(f) If the sun provides 1000 J of energy to the plants, then how much energy will be transferred to fox through the food chain.

Answer:

(a) Green plants Rabbit Fox Lion

(b) (i) The rabbit is the herbivore and (ii) the fox and the lion are the two carnivores in the food chain.

(c) The fox is both a predator of the rabbit and a prey of the lion.

(d) (i) The rabbit forms the second trophic level, and (ii) the fox forms the third trophic level.

(e) The lion can feed on both the rabbit and the fox independently. Hence, it can feed on animals in both the second and third trophic levels.

(f)   The energy available at the trophic level of the fox is 0.1 J.     
       Sun Green plants Rabbit  Fox Lion

       1,000 J  10 J           1 J        0.1 J   0.01 J



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Question 64:

A food chain consists of fish, larvae, phytoplanktons and birds. The level of pesticides in water in which the fish, larvae and phytoplanktons live is quite high.
(a) In which organisms the pesticides enter from the polluted water? What is this level of organisms known as?
(b) Which organism will have the maximum amount of pesticides accumulated through the food chain? What is this process known as?
(c) Write the food chain comprising all the organisms mentioned above.
(d) Which other organism you could write in place of bird in the above food chain?

Answer:

(a) The pesticides enter the phytoplankton from the polluted water. This level of organisms is known as producers.

(b) The birds will have the maximum amount of pesticides accumulated in them through the food chain. This process is known as biomagnification.

(c) Phytoplankton Larvae Fish Birds

(d) Humans also consume fish, and hence they can replace the birds in the above food chain.

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Question 65:

Every household produces a lot of material A daily. In one of the methods of disposal B, material A is burned at a very high temperature of about 1000°C in a structure called C. During this process, the organic matter present is removed as D and E whereas F is left behind (which can be dumped in a landfill site).
(a) What is material A?
(b) Name the method of disposal B.
(c) What is structure C known as?
(d) What are (i) D (ii) E, and (iii) F?
(e) This method is especially suitable for the disposal of materials produced by certain institutions. Name such institutions.

Answer:

(a) Material A is garbage.

(b) Incineration is the name of the method of waste disposal named B.

(c) Structure C is known as an incinerator.

(d) (i) D is carbon dioxide.
(ii) E is water vapour.
(iii) F is ash.

(e) The method of disposing of wastes by burning them is especially suitable for the disposal of hospital wastes.



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