NCERT Exemplar Class 10 Science Solutions Chapter 15 Our Environment

Question:2

In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers
Answer:(a)
In a food chain, the third trophic level is always occupied by carnivores that feed on herbivores.
Tropic levels
1. Producers/autotrophs ---- level - 1
2. Herbivores ---- level – 2
3. Carnivores ---- level – 3
4. Higher Carnivores ---- level – 4
Therefore option (A) is correct

Question:3

An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects
Answer:(c)
The ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall etc.
Ecosystem includes interaction among biotic and abiotic components, i.e., both living organisms and non-living objects.
Therefore option (C) is correct

Question:4

In the given food chain, suppose the amount of energy at the fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 5 k J
(b) 50 k J
(c) 500 k J
(d) 5000 k J
Answer:(d)
According to the 10% law, only 10% of the energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level. So basically, the top level has 10 times more energy than the level we are in
Given 4th trophic level has 5kJ of energy
4^th level has ---------------- 5 k J
3^rd level has ---------------- 5 k J × 10
2^nd level has ---------------- 5 k J × 10 × 10
1^st level has ---------------- 5 k J × 10 × 10 × 10 = 5000 k J
Therefore option (D) is correct

Question:5

Accumulation of non-biodegradable pesticides in the food chain in increasing amounts at each higher trophic level is known as:
(a) eutrophication
(b) pollution
(c) biomagnification
(d) accumulation
Answer:(c)
Bio-magnification is the accumulation of non-biodegradable pesticides in the food chain in increasing amounts at each higher trophic level. Due to bio-magnification poison from one level to another will increase. So if low-level animals are affected then the poison will be carried to the above levels and doses of poison increase leading to negative consequences on the organism.

Therefore option (C) is correct

Question:6

Depletion of ozone is mainly due to
(a) chlorofluorocarbon compounds
(b) carbon monoxide
(c) methane
(d) pesticides
Answer:(a)
Depletion of ozone is mainly due to chlorofluorocarbons (CFCs). These are synthetic chemicals that are used as refrigerants and in fire extinguishers. Ozone is a stable molecule but the presence of chlorofluorocarbons in the atmosphere has led to the ozone hole as it converts ozone molecules to oxygen. The prevalent use of chlorofluorocarbons has led to an ozone hole near the poles.
Therefore option (A) is correct

Question:7

Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores
Answer:(b)
A decomposer is an organism that decomposes or breaks down, organic material such as the remains of dead organisms. Organisms which synthesize their food from inorganic compounds using radiant energy are called producers or autotrophs e.g., all green plants, blue-green algae etc. Animals that eat plants exclusively are herbivores, and animals that eat only meat are carnivores.
Therefore option (B) is correct

Question:8

In an ecosystem, the 10% of 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)
The 10% of energy accessible for transfer from one trophic level to the next in an ecosystem is in the form of chemical energy.
The autotrophs capture the energy present in sunlight and convert it into chemical energy which is passed on to other trophic levels.
Therefore option (C) is correct

Question:9

Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
(a) food web
(b) ecological pyramid
(c) ecosystem
(d) food chain
Answer:(a)
Organisms of a higher trophic level feeding on several types of organisms belonging to a lower trophic level constitute the food web. An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem. An ecosystem is a network of living beings related to the nonliving beings of their environment, interacting as a system. The food chain is a linear sequence of organisms where nutrients and energy are transferred from one organism to the other.
Therefore option (A) is correct

Question:10

The Flow of energy in an ecosystem is always
(a) unidirectional
(b) bidirectional
(c) multi-directional
(d) no specific direction
Answer:(a)
An ecosystem is a network of living beings related to the nonliving beings of their environment, interacting as a system. The energy enters the plants (autotrophs) through photosynthesis during the making of food. This energy is then passed on to other trophic levels in the food chain. The energy moves progressively through various trophic levels so, it may not be available to the previous level. This flow of energy is unidirectional.
Therefore option (A) is correct

Question:11

Excessive exposure of humans to U V-rays results in
(i) damage to the 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)
The UV-rays have extremely harmful effects on human beings, plants as well as animals. It can cause:
1. Skin cancer
2. Cataract: Damaging the eyes
3. Damages the immune system by lowering the body's resistance to diseases.
4. Premature ageing and other skin damage.
Therefore, option (C) is correct

Question:12

In the following groups of materials, which group (s) contains only non-biodegradable items?
(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)
Substances that cannot be broken down by biological processes in nature are non-biodegradable substances, e.g., polythene, detergent, PVC, plastics, Bakelite, DDT etc. On the other hand, substances that can be broken down by biological processes are said to be biodegradable, e.g., wood, paper, leather, grass, animal bones etc.
(ii) and (iv) contain non-biodegradable items.
Therefore option (D) is correct

Question:13

Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy at higher trophic levels
(b) Deficient food supply
(c) Polluted air
(d) Water
Answer:(a)
When we move from one trophic level to another, energy decreases. This is so because energy is lost as metabolic heat when the organisms from one trophic level are consumed by organisms of the next trophic level. In this way, the organism at a higher level gets less and less energy at progressive levels. The number of trophic levels is restricted to 3-4 because, from that point forward, the energy accessible for the following level will be too little, i.e., it will be too small to sustain the life of the organisms. Hence, the decrease in energy at higher trophic levels limits the number of trophic levels in a food chain.
Therefore option (A) is correct

Question:14

Which of the statements is incorrect?
(a) All green plants and blue-green algae are producers
(b) Green plants get their food from organic compounds
(c) Producers prepare their food from inorganic compounds
(d) Plants convert solar energy into chemical energy
Answer:(b)
(a) All green plants and blue-green algae are called producers as they can prepare food from inorganic substances by photosynthesis.
(b) Green plants get their food from inorganic compounds (and not organic compounds).
(c) Producers (green plants) get their food from inorganic compounds using the radiant energy of the sun in the presence of chlorophyll
(d) Producers capture the solar energy and convert it into chemical energy.
Therefore option (B) is correct

Question:15

Which 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)
Ans. (c)
The flow of energy starting with one living being and then onto the next at various biotic levels forms a food chain. A food chain
portrays the feeding connections between the life forms within that ecosystem.
(i) is a forest food chain
Grass — Rabbit — Wolf — Lion
A lion consumes a wolf, a wolf consumes a rabbit and a rabbit consumes grass for energy.
(ii) is an aquatic food chain in which grasshoppers cannot take part. Instead of grasshoppers, Zooplankton should have been given
Plankton — Zooplankton — Fishes — Man
(iii) Wolf, snake and tiger all are carnivores. There is no herbivore to eat grass in this chain. So the initial transfer of energy is missing.
(iv) Grass - Grasshopper - Frog - Snake - Eagle, is a proper food chain.
Therefore option (C) is correct

Question:16

The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about
(a) 1 %
(b) 5 %
(c) 8 %
(d) 10 %
Answer:(a)
The green plants capture about 1% of the energy of sunlight that falls on their leaves for photosynthesis. This is so because photosynthesis is possible only with a very few frequencies in the visible light. So, only 1% of the energy of sunlight that falls on their leaves is captured and converted into food energy.
Therefore option (A) is correct

Question:17

In the given Figure 15.1, the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

(a) T4
(b) T2
(c) T1
(d) T3
Answer:(c)
The maximum energy is available at T₁. There is a progressive decrease in the amount of energy accessible from the producer to higher trophic levels, i.e., T₁> T₂> T₃>T₄. Starting from one level to another, some part of the energy is consumed and the rest is passed to the next generation. 100% effectiveness is not possible so some of the energy is lost starting with one generation and then onto the next.
Therefore option (C) is correct

Question:18

What will happen if deer is missing in the food chain given below?
Grass → Deer → Tiger
(a) The population of tiger increases
(b) The population of grass decreases
(c) Tiger will start eating grass
(d) The population of tigers decreases and the population of grass increases
Answer:(d)
The given food chain is Grass → Deer → Tiger. Tiger is a carnivore so obviously, it cannot feed on the grass to obtain energy. If deer is missing in the given food chain, there will not be sufficient food/energy for the tigers. The tigers will die because of starvation and hence, the population of tigers will decrease. Now as deer is missing, grass consumption will not be there, hence grass will also increase.
Therefore option (D) is correct

Question:19

The decomposers in an ecosystem
(a) convert inorganic material, to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not break organic compounds
Answer:(b)
Decomposers feed on dead remaining parts and byproducts or living beings. These are also called scavengers of nature/environment. The decomposers in an ecosystem convert organic material to inorganic forms, which go into the soil and are once again used up by the plants. Examples of decomposers are fungi, bacteria etc.
Therefore option (B) is correct

Question:20

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 primary consumer
Answer:(c)
The food chain involved is:
Grass – Grasshopper – Frog.
In this food chain, if a grasshopper is eaten by a frog, then the energy transfer will be from the primary consumer to the secondary consumer. Grasshopper feeds on producers, i.e., the grass/plants.
Level - 1 Grass Producer
Level – 2 Grasshopper Primary consumer
Level – 3 Frog Secondary consumer
Therefore option (C) is correct

Question:21

Disposable plastic plates should not be used because
(a) they are made of materials with lightweight
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials
Answer:(d)
Disposable plastic plates should not be used because they are made of non-biodegradable material, i.e., plastic. They can cause pollution, block drains and harm animals. Non-biodegradable materials do not decompose naturally or even artificially by any means. The only thing we can do with non-biodegradable materials is to reduce, reuse and recycle them. So disposable plastic plates should not be used.
Therefore option (D) is correct

Question:22

Why is improper disposal of waste a curse to the environment?
Answer:

Improper disposal of waste is a curse to the environment. Disposal means ‘to get rid of’. Improper disposal of waste adds pollutants to the environment. It can cause harm to human, animal and plant health as it pollutes the air, water and soil. So the entire food chain is affected. Improper waste disposal often contaminates groundwater supplies, lakes, ponds, rivers etc.

Question:23

Write the common food chain of a pond ecosystem.
Answer:

Producers: Rooted or floating plants usually algae, called phytoplankton are the major autotrophs that act as food sources to consumers.
Consumers are of two types:

• Herbivores: Protozoa (zooplankton) which consume algae

• Carnivores: Small fish will consume Protozoa.

Big Fish/Animals/Birds consume the small fish.
So the food chain is as follows:
Algae ---------Protozoa ———Small fish —— Large fish/bird/animal
(Producer) (Herbivore) (Carnivore) (Large carnivore)

Question:24

What are the advantages of cloth bags over plastic bags during shopping?
Answer:

Plastic bags are made of non-biodegradable material, i.e., plastic.

1. They can cause pollution, block drains and harm animals.

2. They do not decompose naturally or even artificially by any means.

Cloth bags have the following advantages over plastic bags

1. These are biodegradable so do not harm the environment.

2. They can be reused over and over again.

Question:25

Why are crop fields known as artificial ecosystems?
Answer:

An artificial ecosystem is a human-made system of plants, animals, and people living in an area together with their surroundings. These are not self-sustainable. So these are modified and managed by human beings. Examples: aquariums, botanical gardens etc. Crop fields are man-made; plants do not grow naturally in crop fields. Most of the plants are grown by humans according to the season, type of soil, needs etc.
In crop fields, the land is managed by humans, the soil is prepared for sowing seeds, and constant irrigation is done to get a good yield. Thus, crop fields are known as artificial ecosystems

Question:26

Differentiate between biodegradable and non-biodegradable substances. Cite examples.
Answer:

Question:27

Suggest one word for each of the following statements/ definitions
(a) The physical and biological world where we live in
(b) Each level of the food chain where the transfer of energy takes place
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
(d) Organisms which depend on the producers either directly or indirectly for food

Ans.
(a) Environment
(b) Trophic level
(c) Abiotic factors
(d) Consumers/heterotrophs
Environment: the surroundings or conditions in which a person, animal, or plant lives or operates.
Trophic Level: Each level of several hierarchical levels in an ecosystem, consists of organisms sharing the same function in the food chain and the same nutritional relationship to the primary sources of energy.
Abiotic factors: non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems.
Heterotrophs: Organisms that depend on the producers/autotrophs either directly or indirectly for food.

Question:28

Explain the role of decomposers in the environment.
Answer:

Decomposers feed on the remains of other organisms. The organisms that feed on dead plants and animals are called decomposers, e.g., bacteria, fungi etc. They break down the complex organic compounds present in the dead remains into simpler substances and obtain nutrition from them. These substances are released into the soil and the atmosphere.
Role of decomposers on the environment:
(i) Help in the recycling of materials
(ii) Help in the replenishment of the soil's nutrients
(iii)They clean up our surroundings by decomposing organisms and organic wastes

Question:29

Select the mismatched pair in the following and correct it.
(a) Bio-magnification — Accumulation of chemicals at the successive trophic levels of a food chain
(b) Ecosystem — Biotic components of the environment
(c) Aquarium — A man-made ecosystem
(d) Parasites — Organisms which obtain food from other living organisms
Answer:

(a) Bio-magnification — Accumulation of chemicals at the successive trophic levels of a food chain. Correct definition.
(b) Ecosystem — Biotic components of the environment – incorrect.
The ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall etc.
(c) Aquarium — A man-made ecosystem – Correct.
(d) Parasites — Organisms that obtain food from other living organisms – Correct.
Therefore option (B) is correct

Question:30

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

A pond or lake is a natural ecosystem. These are self-sustaining and complete. All the organisms of the food chain are available. If any organism dies, there are decomposers to decompose their bodies into simpler substances.
An artificial ecosystem is a human-made system of plants, animals, and people living in an area together with their surroundings. These are not self-sustainable.
An aquarium is an artificial and incomplete ecosystem. The abiotic components are not supplied naturally. It may not have all the biotic components in it. If a fish dies in an aquarium in the absence of a decomposer, it will lie there like a rotten body, polluting the water of the aquarium. Thus, an aquarium needs regular cleaning and maintenance.

Question:31

Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
Answer:

The flow of energy in an ecosystem is unidirectional and occurs in the following sequence:
Sun —— Producer ——— Herbivore —— Carnivore
(i) Energy flows dynamically starting with one trophic level and then onto the next
(ii) Energy cannot return to a trophic level.
(iii)Out of the total energy accessible, at a particular trophic level, only 10% is given to the next trophic level.
(iv) It is impossible for energy to flow in the reverse direction
(v) The accessible energy decreases at a higher trophic level as energy moves from a lower level to a higher level
(vi) Part of the energy is used by an organism for its needs and the remaining part is lost in energy transfer

Question:32

What are decomposers? What will be the consequence of their absence in an ecosystem?
Answer:

Decomposers feed on the remains of other organisms. The organisms that feed on dead plants and animals are called decomposers, e.g., bacteria, fungi etc. They break down the complex organic compounds present in the dead remains into simpler substances and obtain nutrition from them. These substances are released into the soil and the atmosphere.
Role of decomposers on the environment:
(i)Help in the recycling of materials
(ii) Help in the replenishment of the soil's nutrients
(iii)They clean up our surroundings by decomposing organisms and organic wastes.
The outcome of their absence in an ecosystem can be disastrous as:

(i) Accumulation of dead bodies and the accumulation of non-living organisms like plant leaves, fruits, vegetables etc. would take place. This would pollute the environment.

(ii) The components by which bodies are made would never be returned to the soil if these are not decayed by the organism into smaller digestible molecules by decomposers.

Question:33

Suggest any four activities in daily life which are eco-friendly.
Answer:

Eco-friendly activities are those activities that are beneficial for the environment
Four activities in daily life that are eco-friendly are as follows:
(i) Separation of bio-degradable and non-biodegradable wastes: This is a swatch Bharat initiative, you may have noticed dustbins with the green and blue colour where green belongs to biodegradable and blue belongs to non-biodegradable.
(ii) Replace polythene/plastic bags with cloth/paper bags: many cities in India have banned the use of plastic.
(iii) Use of public transport or carpool for commuting, walking or using cycle for short distances, or even using electric bikes.
(iv) Using rainwater harvesting wherever possible.
(v) Switching off lights/fans when not in use, using sunlight in the daytime and using power-efficient equipment.
(vi) Replacing fertilizers with compost and vermicompost to avoid insecticides or pesticides.

Question:34

Give two differences between the food chain and the food web.
Answer:

Question:35

Name the wastes which are generated in your house daily. What measures would you take for their disposal?
Ans
1. Kitchen waste like food, vegetable peel, and fruits all that are biodegradable can be thrown directly in a compost pit and turned into useful humus.
2. Paper waste like newspapers, magazines and textbooks, plastic waste like bottles, Tupperware containers should be reused or should be sent for recycling.
3. Biohazard waste like cotton, band-aids, used tampons, needles, and injections should be disposed of properly in the designated waste area as they may carry disease-carrying pathogens.
4. Vegetable/fruit peels/rind should be placed near trees/plants so that on decomposition they enrich the soil with nutrients.

Question:36

Suggest suitable mechanism (s) for waste management in fertiliser industries.
Ans.
Fertiliser industries produce effluents and harmful gases as main wastes. These are artificially produced so a lot of energy is consumed to make them. These are biologically less absorbable and have a bad effect on human health.
A suitable mechanism for waste management is:
(i) For control of gaseous pollutants combustion equipment is are used for pollutants that can be oxidized. The pollutants are exposed to a high temperature (1650°C) in the process.
(ii) Air pollutants and flammable compounds are controlled through the use of adsorption equipment. Adsorption equipment tries to absorb pollutants on its surface pores and by heating the adsorbents we can release them in a closed chamber and convert the harmful chemicals into less harmful chemicals.
(iii) Decrease the use of fertilizers and try to use natural manures for nutrients in the soil.
(iv) Try to have different crops in an area
(v) Leave the area for some time without any crops which helps in regaining nutrients in the soil.

Question:37

What are the by-products of fertiliser industries? How do they affect the environment?
Ans.
Fertiliser industries produce effluents and harmful gases as main wastes. These are artificially produced so a lot of energy is consumed to make them. The by-products of fertilizer industries are pesticides and some chemical fertilizers. They are non-biodegradable, so they accumulate at each trophic level. These pesticides mix up with the soil and water. Eventually, they get absorbed by the growing plants along with water and minerals. Herbivores consume the plants, so the poisonous chemicals enter the bodies of these herbivores through the food chain. Next, when carnivores eat herbivores, the pesticides get transferred to their bodies.
Humans, being omnivores, eats both plants and herbivores and the fertilizers get accumulate into their body. Thus, pesticides enter the food chain at the producer level and in the process of transfer of food through food chains, they get concentrated at each trophic level. This is called bio-magnification.

Question:38

Explain some harmful effects of agricultural practices on the environment.
Answer:

Some harmful effects of agricultural practices on the environment are as follows:
(i) Soil degradation: loss of soil fertility because of extensive cropping. Some of the nutrients cannot be replaced naturally due to the crop's high demand.
(ii) Pollution: Soil, water and air pollution caused by the use of synthetic fertilizers and pesticides. The majority of pesticides are health hazardous due to bio-magnification. The harm caused increases when we move from lower trophic levels of a food chain to higher trophic levels.
(iii) Water shortage: Excess use of groundwater for agriculture lowers the water table. This makes the underground water go deep into the ground.
(iv) Deforestation: Indiscriminate falling of trees for agriculture has resulted in the loss of habitat for wildlife. A natural ecosystem is damaged because of this.