CBSE Class 10 Science Our Environment VBQs

MCQ Questions for NCERT Class 10 Science Our Environment 

Question. Different types of enzymes are present in our body because:
(i) each enzyme has a specific function
(ii) each enzyme has a specific substrate
(iii) it makes the metabolic process faster
(iv) it makes the replacement of the defective enzymes easy
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i) and (iv)
(d) All of the above

Answer: B

Question. Which food chain is NOT a part of the given food web?
(a) Plants → Frog → Snake → Peacock
(b) Plants → Frog → Snake → Owl
(c) Hydrophytes → Crabs → Fish → Hawk → Tiger
(d) Both A and B

Answer: B

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

Answer: A

Question. Lakes and ponds do not require cleaning but an aquarium does because
(a) an aquarium is an artificial and an incomplete ecosystem
(b) lakes and ponds are natural and incomplete ecosystems
(c) an aquarium possesses a pool of decomposers
(d) lakes do not possess any deomposers and thus BOD always remain low

Answer: B

Question. Name the thing in our body which helps us to digest food?
(a) hormone
(b) enzymes
(c) stomach
(d) mouth

Answer : B

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

Answer : (a), (c) and (d).

Question. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat

Answer : B

Question. Which of the following is an example biodegradable substance?
(a) Glass
(b) Plants
(c) Plastics
(c) Polythene

Answer : B

Question. Which of the following is an example non-biodegradable substance?
(a) Virgin plastic
(b) Plastic
(c) Plants
(d) Plant products

Answer : B

Question. Which of the following is a functional unit of environment?
(a) Ecosystem
(b) Nitrogen
(c) Carbon
(d) Oxygen

Answer : A

Question. Which of the following is an example of herbivores?
(a) Cow
(b) Shark
(c) Lion
(d) Tiger

Answer : A

Question. Which of the following constituents do not form ecosystem?
(a) Biotic constituents
(b) Plastic bags
(c) Abiotic constituents
(d) All of these

Answer : B

Question. In ___________ presence of ____________, along with sunlight is required to make organic compounds.
(a) producers; chlorophyll
(b) decomposers; chlorophyll
(c) producers; carbon
(d) consumers; carbon

Answer: A

Question. All the organisms are not capable of utilising the sun’s energy directly for meeting their energy requirements. This gap is filled by
(i) all green plants
(ii) some species of bacteria
(iii) algae
(iv) all bacterial species and plant species
(a) (ii) and (iv)
(b) (i) and (iii)
(c) (i), (ii) and (iii)
(d) Only (i)

Answer: B

Question. Which of the following would be affected by the decrease in the producer population?
(a) All the organisms in the ecosystem.
(b) The organisms in the next trophic level.
(c) The organisms at the highest trophic level.
(d) None of the organisms in the food chain will be affecte(d)

Answer: A

Question. Four students gave 4 different statements about ecosystem. Who is incorrect?
Student A: “Energy can be recycled in an ecosystem.”
Student B: “Matter cannot be recycled in an ecosystem.”
Student C: “Energy cannot be recycled but matter can be recycled in an ecosystem.”
Student D: “Neither energy nor matter can be recycled in an ecosystem.”
(a) Both students A and B
(b) Students A, B and D
(c) Student C
(d) Students A and C

Answer: B

Question. Why do all food chains start with plants?
(a) Because plants are easily grown.
(b) Because plants are nutritious.
(c) Because plants can produce its own energy.
(d) Because plants do not require energy.

Answer: C

Question. Which of the following sets of substances can be used for vermicomposting?
(a) Glass, sea shells, vegetable and fruit peels
(b) Shells, vegetable peels, fruit peels and paper
(c) Plastic cans, newspapers and cooked food
(d) Styrofoam cups, disposable plates, cooked food and newspapers

Answer: B

Question. Which of the following is not a terrestrial ecosystem?
(a) Forest
(b) Grassland
(c) Desert
(d) Aquarium
Answer : D

Question. With regard to various food chains operating in an ecosystem, man is a:
(a) Consumer
(b) Producer
(c) Producer and consumer
(d) Producer and decomposer
Answer : A

Question. Which one of the following belongs to First trophic level
(i) Sunflower plants
(ii) Cockroach
(iii) Neem tree
(iv) Grasshopper
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (ii)
(d) (ii) and (iv)
Answer : B

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

Question. In the below food chain,5 J of energy was available to Hawks. How much would have
been present in plants Plants -> Rats -> Snakes -> Hawks
(a) 50 J
(b) 5 J
(c) 500 J
(d) 5000 J
Answer : D

Question. Which of the following limits the number of trophic levels in a food chain?
(a) insufficient food supply
(b) Polluted air
(c) water
(d) Decrease in energy at higher trophic levels
Answer : D

Question. Which of the statement is incorrect?
(a) Green plants get their food from organic compounds
(b) All green plants and blue green algae are producers
(c) Plants convert solar energy into chemical energy
(d) Producers prepare their own food from inorganic compounds
Answer : A

Question. Ten percent law was given by
(a) Lindeman
(b) Darwin
(c) Mendel
(d) Morgan
Answer : A

Question. Amount of energy transferred from one trophic level to the next is
(a) 1%
(b) 10%
(c) 20%
(d) 2%
Answer : B

Question. What are the various steps of food chain called
(a) Food chain levels
(b) Tropic levels
(c) Trophic levels
(d) None of these
Answer : C

Question. Food web is constituted by:
(a) relationship between the organisms and the environment
(b) relationship between plants and animals
(c) various interlinked food chains in an ecosystem
(d) relationship between animals and environment.
Answer : C

Very Short Answer Type Questions :

Question. Name the radiations that are absorbed by ozone blanket.
Answer : Ultraviolet (UV) radiations

Question. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals?
Name the phenomenon associated with it. Insects, Hawk, Grass, Snake, Frog
Answer : Among the following organisms of the food chain, hawk being top consumer is present at topmost trophic level, hence will have the highest concentration of non-biodegradable chemicals due to a phenomenon known as biomagnification.

QuestionGive reason why ozone layer in the stratosphere is considered useful?
Answer : Ozone layer in the stratosphere protects the living organisms including man from harmful UV radiations of the sun by absorbing most of them.

Question. Rearrange the given members of food chain in the correct trophic level: frog, grass, snake, insect.
Answer : Grass → Insect → Frog → Snake

Question. Why is excessive use of CFCs a cause of concern?
Answer : CFCs or chlorofluorocarbons are potent compounds that release active chlorine in the atmosphere which reacts with ozone molecules present there to convert them to oxygen. This results in thinning of ozone layer. Hence, excessive use of CFCs is a cause of concern.

Question. We often use the word environment. What does it mean?
Answer : Environment can be defined as the physical or biological world where an organism lives. Literally speaking, an, organism’s immediate surrounding constitutes its environment which includes both biotic and abiotic components around it.

Question. Why are green plants called ‘producers’?
Answer : Green plants are called ‘producers’ because they prepare their own food in the presence of sunlight and chlorophyll by the process of photosynthesis.

Question. Why are plastics non-biodegradable substances?
Answer : Plastics are non-biodegradable substance because they cannot be broken down by the action of enzymes, bacteria or decomposers.

Question. In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer?
Answer : According to ten percent law, 10% of the energy of producer will be available to primary consumer, and 10% of this energy will be available to secondary consumer (100J) and so on.
Producer 10% → Primary 10% → Secondary 10% → Tertiary 
10,000 J consumer consumer consumer 10 J
1,000 J 100 J

Question. Why is lake considered to be a natural ecosystem?
Answer : Lake is an ecosystem where living organisms grow, reproduce and interact among each other as well as with abiotic components and carry out other activities in nature by themselves without any human interference, therefore it is referred to as a natural ecosystem.

Question. Using Kulhads as disposable cups to serve tea in trains, proved to be a bad idea. Why? 
Answer : Making Kulhads on large scales leads to the loss of top soil.

Question. Why is plastic not degraded by bacteria? 
Answer : Plastic is not degraded by bacteria because they do not have enzymes to degrade plastic.

Question. DDT has entered food chain. Which food habit is safer- vegetarian or non- vegetarian? 
Answer : Vegetarian habit is safer. Being closer to producers, less DDT will accumulate in our body.
Bio magnification leads to higher level of DDT in higher trophic levels.

Question. Aquarium requires regular cleaning whereas lakes normally do not. Why? 2 Marks
Answer : Normally a lake has more diverse forms of life and hence a larger number of food chains. This leads to natural cleaning. Thus, the ecosystem is more stable.
The aquarium has a very limited number of food chains and unable to sustain itself.
But, sometimes there is excessive growth of algae in lake. Then it also needs to be cleaned.

Question. How will accumulation of bio degradable waste effect our environment?
Answer : Accumulation of bio degradable waste will:
(a) not let minerals return to mineral pool.
(b) become site of pest breeding

Question. It is the responsibility of the government to arrange for the management and disposal of waste. As an individual you have no role to play. Do you agree? Support your answers with two reasons.
Answer : I do not agree. As an individual, I also have the responsibility and can contribute in the following ways:-
(i) Cut down waste generation.
(ii) Make compost pit for bio degradable waste.
(iii) Recycle non biodegradable waste.

Question. What is meant by biological magnification?
Answer : Biological magnification is the increasing concentration of a substance such as a toxic chemical in the tissues of organisms at successively higher levels in a food chain

Question. Why is the flow of energy in an ecosystem unidirectional? Explain briefly.
Answer : The energy enters the plants from the sun through photosynthesis which is then passed on from one organism to another in a food chain. The flow of energy in an ecosystem is unidirectional because the energy lost as heat from the living orgaisms of a food chain ca ot be reused by plants in photosynthesis.

Question. Give an example to illustrate that indiscriminate use of pesticides may result in the degradation of the environment
Answer : Any suitable example

Question. What will happen if we kill all the organisms in one trophic level?
Answer : 11It will disturb the food chains and food web, which in turn will decrease the chances of food availability to the succeeding trophic levels and will result in instability of the ecosystem.

Question. Which compounds are responsible for the depletion of ozone layer?
Answer : Chlorofluorocarbons (CFCs) are the chemicals which are responsible for the depletion of ozone.

Question. We do not clean ponds or lakes but an aquarium needs to be cleaned regularly. Why?
Answer : There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned

Question. What is a food chain?
Answer : The food chain is a linear sequence of organisms where nutrients and energy is transferred from one organism to the other

Question. Name any two uses of ‘single use plastic’ in daily life.
Answer : Any two uses

Question. Define ‘trophic level’.
Answer : The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In a food chain, each step representing an organism forms a trophic level.

Question. List two natural ecosystems.
Answer : Two natural ecosystems are Lake and River.

Question. Which class of chemicals is linked to the decrease in the amount of ozone in the upper atmosphere of the earth?
Answer : The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons.

Short Answer Type Questions

Question. Mention one negative effect of our affluent life style on the environment.
Answer : Chlorofluorocarbons (CFCs) are the chemicals which are used in refrigerators and air conditioners as coolant when released into the air react with ozone gas present in the ozone layer and destroy it gradually. If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the Sun would reach the earth and cause skin cancer and other ailments in humans, animals and plants.

Question. What are decomposers? List two important roles they play in the environment.
Answer : Decomposers are microorganisms that break down complex organic substances (dead remains and waste products of organisms) into simpler inorganic substances that go into the soil and are used up once more by the plants.
Roles:
1. Decomposers play an important role in the cycling of materials in the biosphere.
By decomposing dead bodies of plants and animals they help in cleansing the environment.
Example, Bacteria and fungi are examples of decomposers

Question. What will be the amount of energy available to the organisms of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?
Answer : According to 10% law, only 10% of energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.
Energy available to 1st Trophic level = 10,000 J
1% of this energy = 100 J
So, First Trophic level has energy = 100 J
Energy to 2nd Trophic level = 10% of 100 J = 10 Joules

Question. List two reasons to show that the existence of decomposers is essential in an ecosystem.
Answer : Role of decomposers:
1. Decomposers naturally replenish the nutrients in the soil, air and water.
2. Decomposers help in keeping the environment clean. They play an important role in the cycling of materials in the biosphere.

Question. State with reason any two possible consequences of elimination of decomposers from the Earth.
Answer : If there were no decomposers, then the dead bodies of plants and animals would keep lying as such and the elements of which plant and animals bodies are made, would never be returned to their original pools like soil, air and water. In that case, the cycling process of life and death would be disrupted. All the nutrients present in soil, air and water would soon be exhausted and evolution of life would come to an end.

Question. We often observe domestic waste decomposing in the bylanes of our homes. List four ways to make the residents aware that the improper disposal of wastes is harmful to the environment and also for their own health.
Answer : The various ways to make residents aware of the harmful effects of improper disposal of wastes are as follows:
• By putting posters and hoardings.
• By distributing pamphlets to the residents.
• By conducting meetings of residents, welfare society, etc.
• By advertisements through TV/radio/cable operators, etc.
• There should be a strict fine imposed by the sanitary officer from the families which
throw their domestic wastes on the roads.
Through all these mediums we can make the residents aware of how such waste serves as a
breeding ground for mosquitoes, releases harmful gases, reduces soil fertility, etc.

Question. List any four disadvantages of using fossil fuels for the production of energy.
Answer : Disadvantages of fossil fuels:
1. Fossil fuels are non-renewable source of energy.
2. The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxides. These acidic gases cause acid rain.
3. The burning of fossil fuels produces smoke which pollutes the air.
The burning of fossil fuels, especially coal, leaves behind a lot of ash.

Question. Write the harmful effects of using plastic bags on the environment. Suggest alternatives to plastic bags.
Answer : Harmful effects of using plastic bags:
• Plastic is non-biodegradable so it will remain as such and pollute the environment.
• Burning of plastic bags produces toxic gases.
• Plastic bags can block the drainage system.
• Discarded plastic bags when eaten by cows and other stray animals can block their alimentary canal and cause harm to them.
Plastic bags when thrown in the water bodies, can cause water pollution as these do not decompose. Cloth bags and bags made from recycled paper should be used in place of plastic bags.

Question. Why are microorganisms like bacteria and fungi important in the ecosystem?
Answer : Microorganisms like bacteria and fungi are important in the ecosystem because they decompose or break down the dead remains of animals and plants. This release the locked nutrients to be recycled in the ecosystem for reuse as raw materials by the producers.

Question. State the consequences of stratospheric zone depletion.
Answer : Stratosphere contains ozone layer which absorbs harmful UV radiations of the sun, protecting the living beings on earth from health consequences of stratospheric zone (ozone) defetion are:
(i) Cancers: UV radiations damage skin cells causing increase in incidences of skin cancer and skin ageing.

Question. Study the given food chain and discuss the effect of removal of any one of the trophic level from it.
Grasses → Deers → Lions
Answer : In the above food chain, if all the lions are removed, the population of deer will increase since there would not be any lion to kill them and to keep the deer population under control. This will lead to high consumption of grasses (producers) and may even eliminate them and if the deer population is removed instead of lions, it will lead to decrease of lion population since there will not be any prey. The lions may even resort to other preys such as domestic animals or man to survive. If the deer and lion operate in other food chains in a food web, then the removal of any one of them will lead to disruption of the food web and will cause disturbance in the ecosystem. In addition if the grasses (producers) are removed, then all life will come to an end. If there is no grass, there will be no herbivores. If there are no herbivores, then there will be no carnivores. Therefore, ultimately all organisms will die.

Question. What is landfilling? How is it beneficial to the environment?
Answer : Landfilling is a method of waste disposal in which solid wastes from urban areas are dumped in low lying areas and compacted by rolling with bulldozers. They are then covered with a layer of soil. Landfilling is an effective method of solid waste disposal in urban areas and at the same time, it helps in reducing the pollution arising out of the waste.

Question. What does a trophic level represent in a food chain? State the position of autotrophs and herbivores in a food chain.
Answer : The various steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic levels.
The position of producers (or autotrophs) in a food chain constitute the first trophic level. They fix up sun’s energy and make it available for consumers. The herbivores or primary
consumers (which feed upon plants) constitute the second trophic level in a food chain.

Question. What will be the consequence of absence of decomposers in an ecosystem?
Answer : In absence of decomposers, recycling of materials will not occur in biosphere. It is due to the reason that decomposers break down the complex organic substances like dead organisms, garbage, etc. into simple inorganic compounds, which go into the soil and used again by plants.
From plants they enter the biosphere through food chain.

Question. Differentiate between food chain and food web.
Answer : Differences between food chain and food web are: 

Question. Producers always occupy the first trophic level in any food chain. Why?
Answer : Producers or green plants have chlorophyll which can trap the solar energy. The first trophic level in a food chain is a producer, i.e., those organisms which can produce food
with the help of sunlight and chlorophyll by a process called photosynthesis.

Question. Why only 4 or 5 trophic levels are present in each food chain?
Answer : The quantum of available energy in a food chain successively gets decreased at each trophic level. There is only 10% flow of energy from one trophic level to the next higher
level. Second law of thermodynamics says that transformation of energy from one form to the other is inefficient and involves dissipation of unavailable energy. This loss of energy
at successive trophic levels restricts the size of food chain in an ecosystem to maximum 4 to 5 steps. Hence, only 4 to 5 trophic levels are present in each food chain.

Question. Grass → Grasshopper → Frog → Snake → Eagle
In the above food chain, which of the organism will have
(i) maximum available energy?
(ii) minimum available energy?
Answer : (i) Grass will have the maximum available energy.
(ii) Eagle will have the minimum available energy.

Question. “Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues.”
State the reason to explain how and why it happens.
Answer : Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants along with water and other mineral’s. When herbivorous animals feed on these plants the poisonous pesticides enter their bodies through the food chain. Similarly, when the carnivorous animals eat these herbivores, the pesticides get transferred to their bodies. Therefore, the plant products such as food grains, vegetables and fruits as well as meat of animals contain varying amounts of pesticide residues depending upon the trophic level they occupy in a food chain.

Question. Write three characteristics of energy transfer in the biosphere?
Answer : The following are the characteristics of energy transfer in the biosphere: (any three)
(i) Energy is supplied by the sun and it is not created in the biosphere. Energy is only converted from one form to another in the biosphere.
(ii) The flow of energy is unidirectional.
(iii) There is loss of energy as we go from one trophic level to the next in an ecosystem. At each transfer, generally 80-90% of energy is lost as heat in accordance with second law of thermodynamics.

Question. Mention the advantages of paper bags over plastic bags.
Answer : The advantages of paper bags over plastic bags are :
(i) Paper bags can be recycled as they are biodegradable.
Their recycling does not produce poisonous gases like recycling of plastic bags.
(ii) Once discarded, paper bags can be recycled again easily, while plastic bags cannot be recycled easily as they clog machines and complicate the recycling processes.
(iii) Plastic bags kill thousands of marine animals every year as some animals confuse plastic bags with jellyfish which block the entrance to the stomach. Paperbags are a healthy, safe alternative to hazardous plastic bags.
(iv) Paper bags are finding favour with all consumers, government and even the environmentalists.

Question. What will happen if all the deers are removed from the given food chain?
Plants → Deer → Tigers
Answer : From the given food chain, if the deers are removed, the population of plants will increase as deers are herbivores and feed on plants whereas the population of tiger (that consume deer) will decrease, as food available for tiger would be less.

Question. Differentiate between biodegradable and non-biodegradable substances.
Answer : Differences between biodegradable and nonbiodegradable substances are: 

Question. (a) From the following group of organisms create a food chain which is most advantageous for human beings in terms of energy.
Hawk, Rat, Cereal plant, Goat, Snake, Human being 
(b) State the possible disadvantage if the cereal plant is growing in soil rich in pesticides.
(c) Construct a food web using the organisms mentioned above.
Answer : (a) A food chain which is most advantageous for human beings in terms of energy is: Cereal plant → Human being
(b) If the cereal plant is growing in soil rich in pesticides, then these pesticides would be absorbed by growing plants along with water and minerals, when animals eat these cereal plants, these poisonous chemical pesticides go into their bodies through food. This increase in concentration of harmful pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification.
Pesticides are lethal to non-target species also. The extensive use of pesticides in agriculture can change the community of microorganisms living in soil.

Question. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer : Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels, e.g., removal of all the producers (T1) will adversely affect all the
types of consumers including herbivores and carnivores, while the removal of all the herbivores will adversely affect only the carnivores but there will be increase in the number of the
producers. No, Removal of all the organisms of any trophic level will always adversely affect the ecosystem, e.g., the removal of lions and tigers (top carnivores) will cause rapid increase in deer population, which will lead to rapid consumption of vegetation resulting in scarcity of vegetation and population crash of deer.

Question. What efforts have been made at international level for mitigating global change?
Answer : Initiatives for mitigating global change are:
Montreal Protocol (16 September 1987) : A landmark international agreement to protect the stratospheric ozone by agreeing to limit the production and use of ozone depleting substances to half the level of 1986 and helping the developing countries to implement use of alternatives to CFCs.
Helsinki Declaration (May, 1989) : Montreal Protocol was ratified by 82 nations at Helsinki. They pledged to phase out CFCs by 2000.
Kyoto Protocol (December, 1997) : International conference held in Kyoto, Japan obtained commitments from different countries for developing alternatives to oxygen depleting substances (ODS) and reducing overall greenhouse gas emissions at a level 5% below 1990 level by 2008-2012. Beijing Protocol (1999) – The protocol lays down steps
to reduce emission of CFCs and other ozone depleting substances. It separates the efforts to be made by developing and developed countries.

Question. Write two causes of depletion of ozone layer.
Answer : Two causes of depletion of ozone layer are :
(a) Use of CFCs (chlorofluorocarbons) in refrigerators and aerosol sprayers.
(b) Release of pollutant nitrogen monoxide by jets.

Question. Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
Answer : Two harmful effects of using plastic bags on the environment:
(i) Plastic bags are non-biodegradable substances which are not acted upon by microbes. So, they cannot be decomposed and therefore persist in the environment for a long time causing harm to the soil fertility and quality.
(ii) Plastic bags choke drains which result in waterlogging, that allows breeding of mosquitoes and hence leads to various diseases.
Jute bags and cloth bags are the alternatives to the polyethene bags.

Question. Why proposal of use of kulhads (disposable cups made of clay) in trains was set aside?
Answer : Sometime back, use of kulhads (disposable cups made of clay) was suggested as an alternative of plastic cups.
However, making of kulhads on such a large scale would have resulted in the loss of top fertile soil. Therefore, this proposal was set aside.

Question. What do you mean by acid rain? Give some effective measures to control it.
Answer : Any precipitation or deposition having a pH lower than 5.6 is called acid rain. Acid rain occurs by the emission of sulphur dioxide and oxides of nitrogen that react with rain water and form acids.
Following measures can be taken to prevent and control acid rain:
(i) Acid rain is mainly caused due to air pollution. Air pollution can be reduced by using pollution-controlling equipment, such as scrubber.
(ii) Other sources for the generation of electricity, such as nuclear fuel or solar power can be used instead of using fossil fuel to reduce the release of oxides of nitrogen and sulphur.
(iii) Cleaner fuels, such as LPG, CNG, etc., could be used in automobiles.
(iv) Use of neutralising agents such as powdered lime stone can be sprayed over areas that are prone to acid rain.

Question. Stability of a biotic community in an ecosystem is inversely proportional to its diversity. Do you agree with this statement?
Answer : No, I do not agree with this statement. Stability of a biotic community is directly proportional to its diversity, number of species and their interactions. Larger the number
of species within a community, more stable it will be.

Question. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?
Answer : An aquarium is an artificial or man-made ecosystem and thus, is not self-regulatory whereas, ponds and lakes are natural, self-sustaining and complete ecosystems. Therefore, ponds and lakes get cleaned by natural processes but an aquarium needs to be cleaned.

Question. Give suitable mechanism(s) for waste management in fertiliser industries.
Answer : Industries involved in making inorganic fertilisers such as urea, potash, etc., cause air and water pollution by releasing harmful and toxic chemicals in air and water during the synthesis of the chemical fertilisers.
Measures required to be adopted for the management of these wastes are :
(i) The release of various pollutants directly in the air should be controlled and minimised by removing particulate matter and gaseous pollutants from foul air before its emission in the source.
(ii) The effluents should be treated and then discharged into the environment. Before discharging them in the water source they should be converted into less harmful, non-toxic materials.

Long Answer Type Questions

Question. Length of food chains in an ecosystem is generally limited to three or four trophic levels. Why?
Answer : Energy flow is always unidirectional, moving successively through trophic levels. Solar energy is received and trapped by autotrophs which passes it to primary, secondary and ertiary consumers. During energy transfer from one trophic level to successive trophic level, 90% of energy is lost and only 10% energy reaches the next trophic level, (Lindemann’s 10% law). Thus, after three or four trophic levels, negligible amount of energy is left to be passed to the next trophic levels. That is why length of food chains is limited to three or four trophic levels only. According to 10% law: If a producer produces 1000 KJ energy, then T2 level (second trophic level) will get 100 KJ, T3 will get 10 KJ of energy, T4 will get 1 KJ and for T5 0.1 KJ energy will be left. More number of trophic levels will get further decreased amount of energy which is neither economical, nor feasible. Thus in nature, length of food chains is generally limited to three or four trophic levels.

Question. Name the wastes which are generated in your house daily. What measures would you take for their disposal?
Answer : The types of waste generated in a house are—
(i) Kitchen wastes like vegetable and fruit peel, rind, used tea leaves.
(ii) Empty milk pouches, polythene bags, empty cartons, etc.
(iii) Waste paper (newspaper, paper bags, packing paper).
(iv) Used tooth picks and ear buds.
(v) Dust and other sweepings.
Measures for household waste disposal–
At an individual’s end following measures should be taken:
(i) Reuse of maximum possible materials
(ii) Separation of biodegradable and non-biodegradable wastes
(iii) Biodegradable wastes should be used for composting
(iv) Non-biodegradable wastes should be disposed off at suitable places from where municipal authorities can pick them up and dispose properly and scientifically. 

Question. “Energy flow in a food chain is unidirectional”.
Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Answer : The producers convert solar energy into chemical energy in the form of organic compounds. The primary consumers (herbivores) derive their nutrition from the producers. According to the energy transfer law, only 10% of energy is transferred from one trophic level to the other. So, the energy that is captured by the producers does not revert to the sun and the energy transferred to the herbivores does not come back to the producers. It just keeps on moving to the next trophic level in a unidirectional way. That is why the flow of energy in the food chain is always unidirectional.
A large number of pesticides and chemicals are used to protect our crops from pests and diseases. Some of these chemicals are washed down from the soil, while some enter the water bodies. From the soil, they are absorbed by plants along with water and minerals; and from the water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain. As these chemicals cannot decompose, they accumulate progressively at each trophic level. This increase in the concentration of harmful chemicals with each step of the food chain is called biomagnification. As human beings occupy the top level in any food chain, these chemicals get accumulated in our bodies.

Question. Explain the phenomenon of ozone depletion. What are the factors responsible for it? What are its consequences?
Answer : Ozone depletion means the thinning of ozone layer in the atmosphere. Many chemicals mainly chlorofluorocarbons are responsible for ozone depletion. These are widely used as coolants in refrigerators and air conditioners; in fire extinguishers; in aerosol sprayer and as propellants. Once released in the air, these chemicals produce `active chlorine’ (Cl and ClO radicals) in the presence of UV radiations. These radicals, through chain reaction, then destroy the ozone by converting it into oxygen. A single active chlorine can deplete one lakh ozone molecules through chain reaction. Thinning of ozone layer allows ultraviolet (UV) radiations to pass through it which then strike the earth and cause harmful effects on man, animals and plants.
(i) UV radiations increase incidences of skin cancer and herpes.
(ii) UV radiations cause damage to eyes resulting in dimming of eye sight.
(iii) Cause damage to immune system hence, lowering the body’s resistance.
(iv) Harmful UV radiations increase mortality of developing embryo in the mothers, uterus.
(v) These radiations decline the rate of photosynthesis in plants which ultimately increase the CO2 concentration leading to global warming.

Case Based Questions :

Read the passage given below and answer the following questions from Various components of an ecosystem maintain a balance in nature. Disturbance in any component of the environment cause an imbalance. One of the main environmental problem caused by human activities is global warming. Global warming is a phenomenon caused by the increasing concentration of greenhouse gases in the atmosphere resulting due to enhanced greenhouse effect.

Question. Study carefully the following figure representing greenhouse effect. 

Select the correct statement regarding this.
(a) Much of the long-wavelength infrared radiations re-radiated by the earth’s surface are absorbed by the atmospheric greenhouse gases.
(b) CO₂, CH₄, CFCs and N₂O are the gases which are responsible for greenhouse effect.
(c) The atmosphere is transparent to the incoming short-wavelength radiations and is translucent to the long-wavelength infrared radiations.
(d) All of these

Answer : D

Question. Greenhouse effect is due to 
(a) accumulation of O₃ and depletion of CO₂
(b) accumulation of both O₃ and CO₂
(c) accumulation of CO₂ and depletion of O₃
(d) presence of green plants on the earth.

Answer : C

Question. Refer to the given pie chart showing the contribution of different gases to global warming.

Identify gases P, Q, R and S and select the incorrect statement regarding them.
(a) P could be a gas that increases in atmosphere due to excessive use of fossil fuel.
(b) Q could be a gas produced by complete combustion of biomass.
(c) R could be synthetic gaseous compounds used as refrigerants in air conditioners and refrigerators.
(d) S could be a gas produced by combustion of nitrogen rich fuel.

Answer : B

Question. What could not be a source of gas Q given in the above pie chart? 
(a) Flooded paddy field
(b) Cattle
(c) Jet fuel
(d) Marshes

Answer : C

Question. If there is no CO₂ in the atmosphere, then what will be the most likely consequence of this on the temperature of earth? 
(a) The temperature remain unchanged as it depends upon the oxygen content of the atmosphere.
(b) The temperature would increase as less greenhouse gases will be absorbed by CO₂.
(c) The temperature would decrease as CO₂ is the principal greenhouse gas.
(d) None of these

Answer : C

Read the passage given below and answer the following questions from Grazing food chains are directly dependent upon solar radiations as the primary source of energy. Green plants (or producers) form the first trophic level of the food chain. They synthesise their food by the process of photosynthesis. Herbivores or primary consumers feed upon the producers and form the second trophic level. Herbivores are eaten by carnivores of different categories. These are longer food chains. Given below are 5 grazing food chains operating in the nature. 

Question. Top consumer in which of the following food chains will have the maximum energy? 
(a) Food chain A
(b) Food chain B
(c) Food chain C
(d) Food chain D

Answer : A

Question. If energy present in producers of food chain D is 20,000 KJ. Then amount of energy present in its secondary consumer will be 
(a) 2000 KJ
(b) 20 KJ
(c) 2 KJ
(d) 200 KJ.

Answer : D

Question. Select the option that correctly identifies P, Q and R. 
         P     Q           R
(a) Frog Deer Aquatic insect
(b) Frog Elephant Phytoplankton
(c) Tadpole Deer Zooplankton
(d) Dog Elephant Algae

Answer : A

Question. According to the given food chains which of the following animals is both secondary and tertiary consumer? 
(a) Rabbit
(b) Tiger
(c) Eagle
(d) Small fish

Answer : B

Question. What will be the shape of pyramid of biomass of food chain E? 

Answer : B

Case Based Questions :

Read the following and answer the following questions. 
Frothing in Yamuna:
The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghats and households. Yamuna’s pollution level is so bad that parts of it have been labelled ‘dead’ as there is no oxygen in it for aquatic life to survive.

Question. The table provides the pH value of four solutions P, Q, R and S: 


Which of the following correctly represents the solutions in increasing order of their hydronium ion concentration?
(a) P > Q > R > S
(b) P > S > Q > R
(c) S < Q < R < P
(d) S < P < Q < R

Answer: C

Question. High content of phosphate ion in river Yamuna may leads to: 
(a) decreased level of dissolved oxygen and increased growth of algae.
(b) decreased level of dissolved oxygen and no effect of growth of algae.
(c) increased level of dissolved oxygen and increased growth of algae.
(d) decreased level of dissolved oxygen and decreased growth of algae.

Answer: A

Question. If a sample of water containing detergents is provided to you, which of the following methods will you adopt to neutralise it? 
(a) Treating the water with baking soda.
(b) Treating the water with vinegar.
(c) Treating the water with caustic soda.
(d) Treating the water with washing soda.

Answer: B

Question. Predict the pH value of the water of river Yamuna if the reason for froth is high content of detergents dissolved in it. 
(a) 10-11
(b) 5-7
(c) 2-5
(d) 7

Answer: A

Question. Which of the following statements is correct for the water with detergents dissolved in it? 
(a) Low concentration of hydroxide ion (OH- )and high concentration of hydronium ion (H3O+)
(b) High concentration of hydroxide ion (OH- )and low concentration of hydronium ion (H3O+)
(c) High concentration of hydroxide ion (OH-) as well as hydronium ion (H3O+)
(d) Equal concentration of both hydroxide ion (OH-) and hydronium ion (H3O+).

Answer: B

Read the following and answer the following questions. 
Biosphere is a global ecosystem composed of living organisms and abiotic factors from which they derive energy and nutrients. The ecosystem is defined as structural and functional unit of the biosphere comprising of living and non-living environment that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity and material cycling to form a stable, self-supporting system. 

Question. The given figure best represents:

(a) Grassland food chain
(b) Parasitic food chain
(c) Forest food chain
(d) Aquatic food chain

Answer: A

Question. Consider the following statements concerning food chains: 
(i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation
(ii) Removal of most of the carnivores resulted in an increased population of herbivores.
(iii) The length of the food chains is generally limited to 3 – 4 trophic levels due to energy loss.
(iv) The length of the food chains may vary from 2 to 8 trophic levels.
Which two of the above statements are correct?
(a) (i), (iv)
(b) (i), (ii)
(c) (ii), (iii)
(d) (iii), (iv)

Answer: C

Question. Which trophic level is incorrectly defined? 
(a) Carnivores–secondary or tertiary consumers.
(b) Decomposers–microbial heterotrophs
(c) Herbivores–primary consumers
(d) Omnivores–molds, yeast and mushrooms

Answer: D

Question. The diagram below shows a food web from the sea shore. 

The mussel can be described as:
(a) Producer
(b) Primary consumers
(c) Secondary consumer
(d) Decomposer

Answer: C

Question. Which of the following groups of organisms are not included in ecological food chain? 
(a) Carnivores
(b) Saprophytes
(c) Herbivores
(d) Predators

Answer: B

Take a look at the picture carefully and answer the following questions. 

Question. Herbivores, carnivores, omnivores, and parasites all come under: 
(a) producers
(b) consumers
(c) ecosystem
(d) food web

Answer: B

Question. Which one is not true about an ecosystem? 
(a) Ecosystem consists of living and non-living things both.
(b) Living organisms interact with each other.
(c) Growth, reproduction, and other activities of living organisms are not affected by the abiotic components of ecosystem.
(d) A garden is considered an ecosystem.

Answer: C

Question. Ecosystems can be of how many types? 
(a) Two types – man-made and natural
(b) Two types – terrestrial and aquatic
(c) Four types – forests, ponds, lakes, and garden
(d) All of the above imply as correct answer.

Answer: D

Question. While designing an aquarium what are the things you would like to include to make it a complete ecosystem? 
(a) Fishes, aquatic plants, pleco fish (algae eating fish), aerator, pebbles, fish food.
(b) Fishes, grass, plants, pleco fish (algae eating fish), fish food.
(c) Fishes, plants, oxygen pump, food, stones.
(d) Animals, fishes, plants, oxygen pump, food.

Answer: A

Question. Which one of the following is not a producer? 
(a) Blue green algae
(b) Cactus
(c) Fungi
(d) Spinach

Answer: C

Read the passage and answer the following questions.
Humans modify the environment around them through agriculture and urbanisation as the major activities. Human impact on the environment is so substantial that there is nothing left called pristine nature or ecosystems untouched by human intervention. The major impact of these interventions is ever increasing levels of all forms of pollution on our Earth. Waste disposal and depletion of ozone layer are two major concerns in this world.

Question. Which one of the following sentences is not true about ozone? 
(a) Ozone is a deadly poison.
(b) Ozone protects us from harmful UV rays emitted by the sun.
(c) Ozone is formed from oxygen in presence of UV rays.
(d) Ozone causes skin cancer in humans.

Answer: D

Question. Which of the following groups contains a non-biodegradable item? 
(a) Grass, flowers, lime-juice, and leather.
(b) Grass, wood, leather, and plastic.
(c) Cake, wood, flowers, and grass.
(d) Fruit-peels, cake, leather, and lime-juice.

Answer: B

Question. Which of the following waste management plan is likely to work the best? 
(a) Integrated waste management plan
(b) Recycling waste management plan
(c) Reducing waste management plan
(d) Reusing waste management plan

Answer: A

Question. Which one of the below given reason holds good for increase in the amount of waste generated by humans? 
(a) Religious practices
(b) Change in packaging style and products
(c) Home cooking
(d) Use of plant-based products

Answer: B

Question. An environment enthusiast would certainly not choose one of these for a tea party at her home. 
(a) Paper cups
(b) Thermocol cup
(c) Steel cup
(d) Earthen cups

Answer: B

Read the following and answer the following questions.
The amount of ozone in the atmosphere has begun to drop sharply from 1980s. This decrease has been linked to synthetic chemicals.
In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze harmful chemicals production at 1986 levels. 

Question. What is the major cause of ozone depletion? 
(a) Chlorofluorocarbons
(b) Hydrochlorofluorocarbons
(c) Carbon tetrachloride and methyl chloroform
(d) All of the above

Answer: D

Question. Which of the following sources is responsible for the depletion of ozone layer? 

 

Answer: D

Question. In which of the following countries Ozone hole has appeared? 
(a) Africa
(b) North America
(c) Japan
(d) Antarctica

Answer: D

Question. At what level of atmosphere ozone layer is found? 
(a) Troposphere
(b) Stratosphere
(c) Biosphere
(d) Ionosphere

Answer: B

Question. At higher level of atmosphere radiations act upon oxygen molecule to form: 
(a) oxygen
(b) ozone
(c) carbon monoxide
(d) all of the above

Answer: B

Read the passage carefully and answer the following questions from The waste generated by humans has been detrimental to our environment and is causing threat to our ecosystem. We are generating too much trash and failing to deal with it in a sustainable way. Every day we are disposing tons and tons of nonbiodegradable and unrecyclable waste into our oceans and landfills. Plastic waste is an example. In 2017 the Environmental Protection Agency in the US calculated that the total generation of municipal solid waste in the United States in 2017 was 267.8 million tons; compared with 2015 levels, it was a 5.7 million increase.

Question. Humans are not supposed to get any energy by eating coal, because: 
(a) coal is harmful.
(b) coal is burnt.
(c) humans do not have enzymes to digest coal.
(d) coal is black.

Answer: C

Question. Man-made plastics are not bio-degradable because:
(a) they are hard.
(b) bacteria and saprophytes do not contain enzymes to decompose plastics.
(c) plastics are made in industries.
(d) plastics do not absorb water.

Answer: B

Question. The depletion in the Ozone layer is caused by _________ . 
(a) nitrous oxide
(b) carbon dioxide
(c) chlorofluorocarbons
(d) methane

Answer: C

Question. Non-biodegradable substances are: 
(a) broken down by biological processes.
(b) not broken down by biological processes.
(c) prepared by biological processes.
(d) cannot be broken down by physical processes.

Answer: B

Question. Which one of the following is not likely to happen in the case of solid waste disposal in landfills? 
(a) Unpleasant odours
(b) Ground water pollution
(c) Fires and explosions
(d) Infrared radiation

Answer: D