CBSE Class 10 Biology Our Environment MCQs Set G

Question. 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

Question. 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

Question. 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

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

Answer: d

Question. What happens to the earth's temperature due to the greenhouse effect? 
(a) Increases
(b) Decreases
(c) Remains the same
(d) All of the above 

Answer: a

Question. Depletion of ozone is mainly due to _________. 
(a) Chlorofluorocarbon compounds.
(b) Carbon monoxide.
(c) Methane.
(d) Pesticides. 

Answer: a

Question. Why is it difficult to degrade non-biodegradable wastes? 
(a) Because non-biodegradable wastes cannot be recycled.
(b) Because microorganisms cannot decompose it.
(c) They can be made into organic wastes.
(d) All of the above 

Answer: b

Question. 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)

Answer: c

Question. Excessive exposure of humans to UV-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

Very Short Answer Type Questions :

Question. List two man-made ecosystems.
Answer: Garden and Aquarium.

Question. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer. 
Answer: Chlorofluorocarbons.

Question. In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes?
Plants → Rats → Snakes → Hawks
Answer: Snakes = 500 x 10/100 = 50 J
Hawks = 50 x 10/100 = 50 J
(According to 10 percent Law)

Question. Why is excessive use of CFCs a cause of concern?
Answer: When CFC’s reach upper layers of the atmosphere, they cause depletion of ozone layer, and allow harmful UV radiations to reach the surface of the earth to create health hazards.

Question. What is the function of ozone in the upper atmosphere?
Answer: Ozone layer protects the earth from harmful radiations like high energy ultraviolet radiations.

Question. Why is forest considered as a natural ecosystem ?
Answer: A forest ecosystem is a natural woodland unit consisting of all plants, animals and micro-organisms, in an area functioning together with all of the nonliving physical factors of the environment.

Question. List two natural ecosystems.
Answer: Natural ecosystem—Forest/Lake/Pond/River.

Question. What is ecosystem? 
Answer: Ecosystem is the functional unit of the environment comprising of the living and nonliving components.

Question. List two biotic components of an ecosystem.
Answer: Plants, animals, micro-organisms.

Question. Write one negative effect, on the environment, of affluent life style of few persons of a society.
Answer: Use of excessive non-biodegradable material in packaging:
Excessive use of natural resources like coal and petroleum which causes pollution.
Affluent lifestyle results in generation of excessive waste materials.

Question. The first trophic level in a food chain is always a green plant. Why?
Answer: Green plants are producers. The first trophic level in a food chain is producer i.e., those organisms which produce food by photosynthesis.

Question. Give reason why a food chain cannot have more than four trophic levels. 
Answer: The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

Question. What is biodegradable substance?
Answer: Substances that can be broken down by microorganisms in natural simple harmless substances.

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: Hawk.
Biomagnification.

Question. Why do producers always occupy the first trophic level on every food chain?
Answer: Because producers (plants) have the ability to trap solar energy with the help of chlorophyll.

Question. Why should biodegradable and non-biodegradable wastes be discarded in two different dustbins?
Answer: (i) Saves time/ energy in segregation.
(ii) Biodegradable items can be sent directly for composting.
(iii) Non-biodegradable items can be sent for a appropriate reuse/recycle.

Short Answer Type Questions :

Question. Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies? What is this phenomenon called?
Answer: Chain of organisms formed as a result of eating or being eaten by organisms is called food chain / A series of organisms feeding on one another, is called food chain. 
Grass → Insect → Frog → Snake
(grasshopper)
(Producer) (Herbivore) (Carnivore) (Top Carnivore) 
(Any other example of food chain)
- Tertiary trophic level / snake
- Biological magnification / Biomagnification

Question. State two advantages of conserving (i) forests and (ii) wildlife. 
Answer: Conserving forests helps in (i) retaining sub soil water and (ii) checking floods/ any other 
Conserving wild life helps in (i) maintaining ecological balance and (ii) protecting the nature

Question. Give any two ways in which biodegradable substances would affect the environment.
Answer: (i) They produce foul smell during decomposition process. 
(ii) They may produce harmful gases such as ammonia, methane and carbon dioxide.

Question. Plastic cups were used to serve tea in trains in early days- these could be returned to the vendors, cleaned and reused. Later, Kulhads were used instead of plastic cups. Now, paper cups are used for serving tea.
What are the reasons for the shift from Plastic to Kulhads and then finally to paper cups?
Answer: Plastic cups are non-biodegradable and harm the environment. They were, thus, replaced by Kulhads.
Making Kulhad, which is made of clay on a large scale resulted in the loss of top fertile soil.
Now, disposable paper cups are used because the paper can be recycled, it is biodegradable and is eco-friendly material, which does not cause environmental pollution.

Question. How can you help in reducing the problem of waste disposal? Write any two methods.
Answer: Segregation of waste at the point of its generation for convenient disposal.
Change in attitude producing less waste by adopting 3 R's policy.

Question. How will you create an artificial aquatic ecosystem, which is self-sustainable? 
Answer: (a) Large jar filled with water, oxygen, food and aquatic plants and animals.
(b) Oxygen/oxygen pump.
(c) Fish food.
(d) Aquatic plants/Producers provide O2 during photosynthesis.
(e) Aquatic animals/Consumers release CO2 for the process of photosynthesis.
(f) Decomposers are also important for natural cleaning of the aquarium.

Question. With the help of an example of a food chain, prove that the flow of energy in the biosphere in unidirectional.
Answer: Sun 1% Energy → Producer/Plant 10% Energy →
Primary consumer/Herbivore 10% Energy →
Secondary consumer/Carnivore 10% Energy → Top Carnivore.
(1) At each trophic level only 10% of the energy is passed on to the next and the rest is either utilized for its own metabolic activities or is lost in the environment as heat.
(2) Lost energy is not returned to the previous level/ Solar input.

Question. Why are bacteria and fungi called decomposers?
List any two advantages of decomposers to the environment? 
Answer: Bacteria and fungi break down/decompose the dead remains and waste products or organisms. 
Advantages:
(i) Natural replenishment of soil.
(ii) Recycling of nutrients in the soil.

Question. The flow of energy between various components of the environment has been extensively studied.
Give an outline of the findings.
Answer: (i) Flow of energy is unidirectional.
(ii) Terrestrial plants take about 1% of the Sun’s energy and change it to chemical energy.
(iii) A great amount of energy is lost as heat/ used for digestion/doing work/growth and reproduction.
(iv) Only 10% of organic matter present at each trophic level (and available to the next trophic level).
(v) Food chains are mainly of 3-4 trophic levels (because of 10 percent law).
(vi) The number of producers are maximum (the number reduces in subsequent trophic levels).
(vii) Food webs are more common (as compared to isolated food chains).
(viii) Biological magnification can be observed.

Question. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes, but an aquarium needs to be cleaned regularly. Why is it so? Explain.
Answer: Ecosystem is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non–living constituents of the environment.
Two main components of Ecosystem are:
(i) Biotic component
(ii) Abiotic component
An aquarium is an artificial and incomplete ecosystem compared to pond or lakes which are natural, self–sustaining and complete ecosystem where there is a perfect recycling of materials.
We need to clean the aquarium because of the:
(i) absence of natural decomposer.
(ii) stagnancy of water.

Question. (i) Create a terrestrial food chain depicting four trophic levels.
(ii) Why do we not find food chains of more than four trophic levels in nature? 
Answer: A food chain showing Ist trophic level , IInd trophic level (½ mark), IIIrd trophic level (½ mark) and IVth trophic level .
A flow chart or a diagrammatic representation showing all the four tropic levels would also be accepted.
According to the 10% law, the amount of energy available will not be sufficient for the survival of the organism in the 5th trophic level.

Question. Give reason to justify the following:
The existence of decomposers is essential in a biosphere.
Answer: The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants.
Thus, decomposer:
(a) replenish the soil naturally,
(b) helps in removing the biodegradable waste.

Question. Your mother always thought that fruit juices are very healthy for everyone. One day she reads in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health.
(a) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit may cause harm and damage our organs Name the phenomenon and write about it.
Answer: (a) (i) Farmers generally use pesticides on fruit crops to protect their crops from plant diseases.
However, pesticides may contaminate the fruit and therefore fruit juices also become contaminated. 
(ii) Using contaminated ground water for irrigation also makes the fruits infected with contaminants. 
(b) Biological magnification or biomagnification is the accumulation of chemicals in the individuals of higher trophic level. Chemicals are nonbiodegradable and their concentration increases at each trophic level. Humans, being at the top of food chain, also receive higher concentration of these harmful chemicals resulting into various health problems.

Question. (a) State with reason the consequence of decrease in number of carnivores in an ecosystem.
(b) In a food chain, state the trophic level at which the concentration of harmful chemicals is maximum. Why is it so?
Answer: (a) The carnivores keep the populations of other carnivores and herbivores help to keep check. If there were no carnivores, the herbivore populations would rise exponentially and they will rapidly consume large amounts of plants and fungi, growing until there is not enough food to sustain them. Eventually, the herbivores would starve, leaving only those plants that were distasteful or poisonous to them. Species diversity would, therefore, drop dramatically.
(b) The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification. The level of biomagnification would increase as the trophic level increases and would be highest for topmost trophic level. It is because certain harmful substances, usually ones not found in nature but introduced by man, may get accumulated into plants and/or animals. These poisonous substances may not be broken down in the body or excreted easily. Instead, they accumulate in the tissues, and as the living organism eats more, the concentration of these substances increases and pass from one trophic level to the next. The maximum concentration is accumulated at the top carnivore’s level.

Question. Students in a school listened to the news read in the morning assembly that the mountain of garbage in Delhi, suddenly exploded and various vehicles got buried under it. Several people were also injured and there was traffic jam all around. In the brain storming session, the teacher also discussed this issue and asked the students to find out a solution
to the problem of garbage. Finally they arrived at two main points – one is self management of the garbage we produce and the second is to generate less garbage at individual level.
(a) Suggest two measures to manage the garbage we produce.
(b) As an individual, what can we do to generate the least garbage? Give two points.
(c) List two values the teacher instilled in his students in this episode. 
Answer: (a) Incineration/Waste compaction/Biogas generation/ Composting/Segregation and safe disposal/ Vermicomposting 
(b) Reuse of empty bottles, books etc.
Reduce the use of non-biodegradable substances like polythene, thermocol, etc. 
(c) Awareness about environment, scientific attitude, concern for community health and personal health.

Question. Write the essential function performed by ozone at the higher levels of the Earth’s atmosphere?
How is it produced? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced?
Answer: It shields the surface of the earth from the UV radiation from the sun.
O₂ → UV O + O
O₂ + O → O₃ {or description of this process in words} 1
Chloro Fluoro Carbons (CFC’s) 
Reduce the use of CFC’s by minimizing the leakage through air conditioners and refrigerators / finding substitute chemicals that are ozone friendly Ozone protects the surface of earth from harmful ultraviolet (UV) radiations emitted by the sun.
Ozone is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms. These atoms combine with molecular oxygen to form ozone.
O₂ → UV O + O
O + O₂ → O₃
(Ozone )
Chlorofluorocarbons (CFCs) are mainly responsible for the drop of amount of ozone in the atmosphere.
Use of these chemicals can be reduced by using alternate products that do not harm the ozone layer. Also, safe disposal of old appliances like refrigerators prevents its emission.

Question. How is ozone layer formed? State its importance to all life forms on earth? Why the amount of ozone in the atmosphere dropped sharply in the 1980s?
Answer: Formation of ozone in Atmosphere: Ozone is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere. The high energy ultraviolet radiations split ozone into molecular and atomic oxygen with large amount of heat. This heat is used in warming the stratosphere.
O₃ → O₂ + [O] + Heat
This oxygen atom then recombine with oxygen (O2) molecule to form ozone molecule.
O₂ + [O] → O₃
The ozone layer acts as a protective blanket around the earth which shields the entire earth from harmful ultraviolet radiations that come from the sun.
Ozone depletion is the reduction in concentration of ozone layer. It is formed due to an increased concentration of ozone-depleting substances such as chlorofluorocarbons (CFCs). CFCs are used in refrigerants, ACs, fire extinguishers, aerosols spray etc.

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose off the waste produced in our homes.
Answer: (a) Harmful effects of plastic bags:
(i) Plastics do not undergo degradation, thus stay in soil for many years. This may affect the soil fertility and degrades the soil quality.
(ii) When plastic artifacts enter the drainage and sewerage system, they block the pipes and drains causing water logging.
(iii) Littering of plastics in open spaces creates unhygienic conditions, as it acts as breeding ground for insects and mosquitoes. 
We can reduce the use of plastic bags and carry jute bags and paper bags to carry items from the market.
(b) Measures taken for proper disposal of waste produced at our homes are:
(i) Prepare a compost pit for kitchen wastes.
(ii) Safe disposal of plastic bags.
(iii) Segregation of biodegradable and non biodegradable wastes.
(iv) Fruit peels can be placed near trees or plants, which on decomposition will enrich the soil with nutrients.
(v) Recycling of paper wastes.

Long Answer Type Questions :

Question. Suggest suitable mechanisms for waste management in fertiliser industries.
Answer: Effluents and harmful gases are the major pollutants which are generated in a fertiliser, chemical or pesticides factory. Scientific mechanism for reduction in emission of pollutants in environment is :
For reduction of gaseous pollutants, electro-static precipitators (ESP) are commonly used. ESP works on the principle of "opposite charges attract."
When the gaseous emissions containing unburnt pollutants such as coal particles, unburnt carbon, SOx, NOx, etc. enters this field, ash particles gets charged and attracted towards the collecting plates due to the force produced by the electric field.
Thereby, reducing the gaseous emissions in the atmosphere. 
In addition to this, industrial waste water generated from the fertiliser industry contains pollutants that may contaminate our natural water resources. For safe disposal of industrial waste water, effluent treatment plant (ETP) is set up to treat the waste water. An ETP is used to purify water and remove any toxic and non-toxic materials or chemicals from
it. They use evaporation and drying methods, and other auxiliary techniques such as centrifuging, filtration, incineration for chemical processing and effluent treatment. The treated water can be used in the industrial process and for irrigation of plantation.

Question. Explain some harmful effects of agricultural practices on the environment.
Answer: Some harmful effects of agricultural practices on the environment are :
(i) Excess use of ground water for agriculture lowers the water level. 
(ii) Excessive use of fertilisers affects the soil pH and kills useful microbes. 
(iii) Excessive use of chemical pesticides lead to biomagnification.
(iv) Extensive agriculture causes loss of soil fertility. 
(v) Burning of agricultural waste like paddy and wheat straw results into the formation of smog that pollutes environment substantially. 
(v) It affects our natural eco-system.

Question. (a) Indicate the flow of energy in an ecosystem.
Why is it unidirectional? Justify.
(b) What will happen if decomposers are absent in an ecosystem?
Answer: (a) The flow of energy is generally from Sun → producer → herbivore → carnivore.
Since the flow of energy is progressively from one trophic level to another and does not revert back, it is said to be unidirectional. Further, the available energy decreases in the higher trophic levels making it impossible for energy to flow in the reverse direction.
(b) Decomposers include micro-organisms such as bacteria and fungi that obtain nutrients by breaking down the remains of dead plants and animals.
It breaks down the complex organic substances of garbage, dead animals and plants into simpler inor ganic substances that go into the soil and are used up again by the plants.
In the absence of decomposers, recycling of material in the biosphere will not take place.

Question. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 
Answer: Ozone layer is a protective shield around the Earth.
It prevents harmful ultraviolet radiation of the Sun from reaching the Earth. Air pollutants, like chlorofluorocarbons (CFCs), are causing depletion of ozone layer.
Depletion of ozone layer is allowing greater amount of UV radiation to reach the Earth. UV radiation can affect the ecosystem by affecting photosynthesis in plants, destroying planktons and decomposers. In human beings, UV radiation may cause skin cancer, cataract and damage to immune system.
Many developed as well as developing nations of the world have agreed to sign and obey the directions of UNEP (United Nations Environment Programme) to cease the production of CFCs or to limit their production to some extent.

Read the following passage and answer the questions given below :
Human body is made up of five important components, of which water is the main component.
Food as well as potable water is essential for every human being. The food is obtained from plants through agriculture; Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradable, they get accumulated progressively at each trophic level.
The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

Question. Various steps in a food chain represent: 
(a) Food web
(b) Trophic level
(c) Ecosystem
(d) Bio-magnification

Answer: b

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. The maximum concentration of pesticides are found in 
(a) Man
(b) Plants
(c) Deer
(d) Tiger

Answer: a

Question. Which of these methods could be applied to reduce our intake of pesticides through food to some extent ? 
(a) Organic farming
(b) Mixed cropping
(c) Single cell protein
(d) Biofortification

Answer: a

Read the given passage and answer the questions given below :
A farmer is growing a crop regularly in his field. He uses chemical fertilizers, pesticides, organic manure as well as bio-fertilizers. Very close to his field is a factory which emits smoke as a byproduct. There is also a huge lake in the nearby area.

Question. A considerable increase in plant life in the lake was noticed after the farming activity intensified. 
The most likely reason for this could be:
(a) Chemical fertilizers leached into the lake from the field.
(b) Pesticides leached into the lake from the field.
(c) Organic manure leached into the lake from the field.
(d) Smoke particles from the industry got settled in moist surroundings of the lake.

Answer: a

Question. An expert agriculturist suggests to the farmer to minimize the use of chemical fertilizers and instead use biofertilizers as they have many advantages over chemical fertilizers. 
Which of the following is NOT true for biofertilizers?
(a) They are economical
(b) They help in reducing pollution in the lake
(c) They are renewable
(d) They require large set-up for their production.

Answer: d

Question. Consider the following food chain in the same lake. 
Aquatic plant → Small fish → Big fish → Birds
Which of the above organisms is likely to show minimum amount of pesticide concentration in them after considerable time?
(a) Aquatic plants.
(b) Small fish.
(c) Big fish.
(d) Birds.

Answer: a

Question. ___________ is the increase in the concentration of harmful chemical substances in the body of living organisms. 
(a) Biological oxygen demand
(b) Biomagnification
(c) Biosynthesis
(d) Biogeochemical cycle

Answer: b