CBSE Class 10 Science Our Environment Assignment Set B

Read and download free pdf of CBSE Class 10 Science Our Environment Assignment Set B. Get printable school Assignments for Class 10 Science. Class 10 students should practise questions and answers given here for Chapter 15 Our Environment Science in Class 10 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 10 Science prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

Assignment for Class 10 Science Chapter 15 Our Environment

Class 10 Science students should refer to the following printable assignment in Pdf for Chapter 15 Our Environment in Class 10. This test paper with questions and answers for Class 10 Science will be very useful for exams and help you to score good marks

Chapter 15 Our Environment Class 10 Science Assignment

MCQ Questions for NCERT Class 10 Science Our Environment 

Question. In 1987 the ---------------------- Succeeded in forging an agreement to freeze CFC Production
(b) UNEP
Answer. B

Question. O2---------UV---------→O+O O+O2---------→O3 (Ozone) The role of UV rays in this reaction is ---------
(a) To Split Oxygen molecule
(b) To unite oxygen molecule
(c) To Destroy Ozone
(d) None
Answer. A

Question. O3---------???---------→ O2 + (O+O) which substance catalyzes the reaction?
(a) Chlorine
(b) Sulphurdioxide
(c) Hydrogen sulphide
(d) Neon
Answer. A

Question. Study the image and answer the questions given below.
CBSE Class 10 Biology Our Environment Management Of Natural Resourcesp

(10000 KJ) (1000 KJ) --------- ????
A. Find out the energy available to the bird :
(a) 100KJ
(b) 10 KJ
(c) 1KJ
(d) 5KJ
Answer. A

Question. Which trophic level may have higher Biological Magnification :
(a) Grass
(b) Snake
(c) Bird
(d) Rabbit
Answer. B

Question. What may happen if all the Rabbits disappear from the ecosystem :
(a) Bird population declines
(b) Snake population declines
(c) Bird and snake population declines
(d) Bird and snake population declines and grass grow abundant
Answer. C

Question. Which of the following chemicals cause Biological Magnification :
(a) DDT
(b) BHC
(c) All non biodegradable pesticides and chemicals
(d) Plastics
Answer. D

Question. Which group of waste materials can be classified as non-biodegradable ?
(a) Plant waste, used tea bags
(b) Polyethene bags, plastic toys
(c) Used tea bags, paper straw
(d) Old clothes, broken footwear
Answer. B

Question. Environment includes:
(a) Land, air, water
(b) Light, temperature, rainfall
(c) Plants, animals, microbes
(d) All of these
Answer. D

Question. Fish diet can play significant role in biological magnification of pesticides like DDT because
(a) harmful chemicals get washed into water bodies and enter the aquatic food chains
(b) fishes can also produce these chemicals in their bodies
(c) fishes increase in number rapidly
(d) fishes have special enzymes in their body to digest these pesticides

Answer: A

Question. The amount of a chemical used in a farmland was in nanograms.
But its amount was found to be in milligrams in higher tropical levels. This happened because ___________.
(a) of biological magnification
(b) of the existence of the food web
(c) organisms of lower trophic levels were consumed by the organisms of higher trophic levels
(d) All of the above

Answer: D

Question. Which of the following are environment friendly practices ? 
(a) Carrying cloth bags to put purchases in while shopping.
(b) Switching off unnecessary lights and fans.
(c) Walking to school instead of getting your mother to drop you on her scooter.
(d) All of the above

Answer: D

Question. Which activity would gradually reduce the occurrence of pests, thereby reducing damage to the crops year by year without affecting the environment?
(a) Use of nitrogen based fertiliser
(a) Crop rotation
(a) Use of DDT
(a) Use of manure

Answer: B

Question. Several factories were pouring their wastes in rivers A and B. Water samples were collected from these two rivers. It was observed that sample collected from river A was acidic while that of river B was basic. The factories located near A and B are :
(a) Soaps and detergents factories near A and alcohol distillery near B.
(b) Soaps and detergents factories near B and alcohol distillery near A.
(c) Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
(d) Lead storage battery manufacturing factories near B and soaps and detergents factories near A.

Answer: C

Question. Some wastes stay in the environment for a longer duration because
(a) they are non-biodegradable materials and decomposers cannot decompose them
(b) they are biodegradable materials but decomposers do not act on these materials
(c) these play role in maintaining ecological balance
(d) these are recyclable

Answer: A

Question. The government of a country banned the use of plastic bags at various places. Is this step justified? Why?
(i) No; because it will not affect the environment in any manner.
(ii) Yes; because it will reduce the amount of non-biodegradable waste (plastic) in the environment.
(iii) Yes; because it will reduce the cost of waste management.
(iv) Yes; because it would be replaced with paper bags which are more economical.
(a) (i)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (ii), (iii), and (iv)

Answer: B

Question. The maximum number of levels in a food chain can be
(a) 7 – 8
(b) 5 – 6
(c) 3 – 4
(d) 1 – 3

Answer: C

Question. A large number of food chains are interconnected because the organisms at the higher trophic level can depend on different types of organisms at the lower trophic level. The existence of this phenomenon in nature is called
(a) food chain
(b) ecological balance
(c) ecological pyramid
(d) food web

Answer: D

Question. Which of the following sets contain only non-biodegradable materials?
(a) Wood, detergent, leather
(b) Polythene, detergent, paper
(c) DDT, plastic, bakelite
(d) Plastic, bakelite, kitchen waste

Answer: C

Question. Which of these is NOT a correct sequence of a food chain?
(a) Phytoplanktons → Zooplanktons → Fish
(b) Seed grains → Rodents → Eagle
(c) Grass → Insects → Frog → Snake
(d) Seaweed → Zooplanktons →Phytoplanktons

Answer: D

Question. In the following groups of materials, which groups contain only nonbiodegradable items ?
(i) Wood, paper, leather
(ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass
(iv) Plastic, bakelite, DDT
(a) (iii)
(b) (iv)
(c) (i), (iii)
(d) (ii), (iv)

Answer: D

Question.  _________ is a biodegradable substance.
(a) Polythene
(b) Paper
(c) Plastic
(d) Glass

Answer: B

Question. The _________ is the functional unit of environment.
(a) genus
(b) ecosystem
(c) class
(d) biome

Answer: B

Question. The % 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

Question. Assertion: The flow of energy is unidirectional.
Reason: Energy as it progresses through the various trophic levels is no longer available to the previous level.
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false, but reason is true.

Answer: A

Question. The decomposers in an ecosystem: 
(a) Do not breakdown organic compounds
(b) Convert inorganic material to simpler forms
(c) Convert organic material to inorganic forms
(d) Convert inorganic materials into organic compounds
Answer:  C
Explanation: The decomposers in an ecosystem are microorganisms, comprising bacteria and fungi. They break down the complex organic substances (dead remains and waste products of organisms) into simple inorganic substances, which go into the soil and are used up once more by the plants.
Question. Ozone layer is mainly damaged by: 
(a) Carbon dioxide
(b) CFCs
(c) Methane
(d) Sulphur dioxide
Answer:  B
Explanation: The use of chemicals like CFCs has endangered the ozone layer. The decrease in the amount of ozone in earth's atmosphere has been linked to synthetic chemicals like chlorofluorocarbons (CFCs). CFCs are used as refrigerants and in fire extinguishers.
Question. Which of the following constitutes a food chain? 
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Grass, fish and goat
(d) Goat, cow and elephant
Answer:  B
Explanation: The following chain constitutes a food chain (organisms in order of who eats whom); a food chain always starts with photosynthesis. Grass is at the first trophic level. Grass fixes up the solar energy and makes it available for the consumers - Goat and Humans. Goat - a consumer - cannot occupy the first trophic level.
Grass →Goat  →Human 

Fill In The Blank

Question. Hydrosphere, lithosphere and atmosphere along with living organism form .......... .
Answer: Biosphere

Question. Nitrates and nitrites present in the soil are changed into ........ by micro-organisms.
Answer: Ammonia

Question. The sequential process of one organism consuming the other forms a .......... .
Answer: Food chain

Question. The physical factors like temperature, rainfall, wind and soil of an ecosystem are the .......... factors.
Answer: abiotic

Question. Decrease in ozone concentration has been linked to synthetic chemicals like .......... which are used as .......... in the refrigerators.
Answer: chlorofluorocarbons, refrigerants

Question. In an ecological pyramid, the base represents ......... level.
Answer: Producer

Question. ......... and ......... are the biotic components of ecosystem.
Answer: Plants, animals

Question. In nature, all green plants are ......... whereas animals are consumers.
Answer: Producers

Question. Ozone is a molecule formed by .......... of ..........
Answer: oxygen, atmosphere

Question. .......... act as scavengers of environment.
Answer: Decomposers

Question. The plants trap .......... energy and convert it into .......... energy.
Answer: Light, chemical

Question. Without the .......... in a food web many chemicals would not be recycled.
Answer: Decomposers

Question. The energy available at each successive trophic level is .......... of the previous level.
Answer: 10%

Question. The physical and biological world where we live in is called .........
Answer: ecosystem

Question. Harmful by products of fertiliser industries are ......... and ..........
Answer: SO2, NO

Question. Nitrogen-fixing bacteria live in nodules on the roots of .......... plants.
Answer: Leguminious

Question. The increased nitrogen in rivers and lakes boosts the growth of ......... and other phytoplankton at the cost of other aquatic organism.
Answer: Algae

Question. Waste substances that are broken down by microbes are called ..........
Answer: Biodegradable

Assertion-Reason Type Questions

For question numbers 2 two statements are given-one labeled as Assertion (A) and the other labeled
Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.

Question. Assertion: Aquarium needs regular cleaning
Reason: There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned.
Answer : A

Question. Assertion: The concentration of harmful chemicals is least in human beings.
Reason: Man is at the apex of the food chain.
Answer : D


Food chains are very important for the survival of most species.When only one element is removed from the food chain it can result in extinction of a species in some cases.The foundation of the food chain consists of primary producers.Primary producers or autotrophs,can use either solar energy or chemical energy to create complex organic compounds,whereas species at higher trophic levels cannot and so must consume producers or other life that itself consumes producers.Becaus the sun’s light is necessary for photosynthesis,most life could not exist if the sun disappeared.Even so,it has recently been discovered that there are some forms of life,chemotrophs,that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents,thus showing that some life may not require solar energy to thrive.

Question. If 10,000 J solar energy falls on green plants in a terrestrial ecosystem,what percentage of solar energy will be converted into food energy?
(a) 10,000J
(b) 100 J
(c) 1000 J
(d) It will depend on the type of the terrestrial plant
Answer : B

Question. Matter and energy are two fundamental inputs of an ecosystem. Movement of
(a) Energy is by directional and matter is repeatedly circulating
(b) Energy is repeatedly circulating and matter is unidirectional
(c) Energy is unidirectional and matter is repeatedly circulating
(d) Energy is multidirectional and matter is bidirectional
Answer : C

Question. Raj is eating curd/yoghurt. For this food intake in a food chain he should be considered as occupying
(a) First trophic level
(b) Second trophic level
(c) Third trophic level
(d) Fourth trophic level
Answer : C

Question. Which of the following, limits the number of trophic levels in a food chain
(a) Decrease in energy at higher trophic levels
(b) Less availability of food
(c) Polluted air
(d) Water
Answer : A

Question. The decomposers are not included in the food chain. The correct reason for the same is because decomposers
(a) Act at every trophic level at the food chain
(b) Do not breakdown organic compounds
(c) Convert organic material to inorganic forms
(d) Release enzymes outside their body to convert organic material to inorganic forms
Answer : A

Very Short Answers

Question. Which of the following belong to the same trophic level: Grasshopper, Spider, Grass, Hawk, and Lizard? 
Answer:  Grasshoppers and Spider belong to the same trophic level i.e. second trophic level.

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 nonvegetarian?
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?
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. What is meant by ‘biological magnification’?
Answer: Biological Magnification is the process by which the harmful and toxic substances enter the food chain and get concentrated in the body of living organisms at each successive level in food chain.

Question. Write a fresh water food chain. 
Answer:  Phytoplankton →Zooplankton →Small fish →Large fish

Question. Give one method which could be applied to reduce our intake of pesticides through food to some extent.
Answer : 
By using biological methods for controlling insects in fields and by washing fruits and vegetables before eating could help to reduce our intake of pesticides through food to some extent.

Question. Why is a 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. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producers?
Plants → Deer → Lion
Answer : 
As per 10% law of flow of energy in an ecosystem only 10% of energy is received by the next trophic level. Hence, in the given food chain : If 100 .J of energy is available to lion, the plants or producers have 10,000 J of energy available to them.
  Plants      →     Deer     →    Lion
10,000 J          1000 J           100 J

Question. What is an ecosystem?
Answer : 
An ecosystem is defined as a structural and functional unit of the biosphere. It comprises of living organisms and their non-living environment that interact by means of food chains and biogeo-chemical cycles resulting in energy-flow, biotic diversity and material cycling to form stable self-supporting system.

Question. Why do producers always occupy the first trophic level in every food chain?
Answer : 
Producers are the green plants that can manufacture food using CO2 and H2O in the presence of sunlight, i.e., they are autotrophs. They serve as a source of food for all nonproducers or consumers directly or indirectly. Hence, producers occupy the first trophic level in a food chain.

Question. Which will get more energy, secondary consumers or tertiary consumers?
Answer : Secondary consumers will get more energy.

Question. Select two non-biodegradable substances from the following waste generated in the kitchen:
Spoil food, Paper bags, Milk, Tea bags, vegetable peels, tin cans, used tea leaves.
Answer : 
Tea bags and tin cans.

Question. List two steps that should be taken for the maintenance of healthy environment.
Answer : (i) Controlling pollution (ii) Afforestation (iii) Proper Waste Disposal

Question. Why are bacteria and fungi called decomposer?
Answer : Bacteria and fungi are called decomposer because they breakdown complex organic matter as remains of plants and animals into CO2, methane and other simple molecules which go into atmosphere and as nutrients to soil

Question. Consider the following food chain which occurs in forest: Grass → Deer → Lion If 10000 J of solar energy is available to grass, how much energy would be available to deer to transfer to lion.
Answer : Grass will absorb 1% solar energy i.e.10000 × 1/100 = 100 J
Dear will get 10% of 100 J =100 × 10/100 = 10 J
Out of this 10 J of energy, only 1 J of energy can be transferred to lion.

Question. Why do producers always occupy first trophic level of food chain?
The first trophic level in a food chain are always occupied by green plants, why?
Answer : They prepare their own food from CO2, H2O and sunlight from environment. They are consumed by herbivores, therefore they always occupy first trophic level.

Question. “Save the Tiger” campaign is being over emphasised these days by our government. What may be possible reason?
Answer : It helps to maintain ecological balance in nature and also to preserve gene pool of a particular species.

Question. In a food chain of frog, grass, insect and snake, assign trophic level to frog.
Answer : Grass → Insect → Frog → Snake
Frog is a secondary consumer and belongs to 3rd trophic level.

Short Answers

Question. Pesticides like DDT which are sprayed to kill pests on crops are found to be present in the soil, ground water, water bodies etc. Explain. How do they reach these places?
Answer. Soil: Pesticides are used to protect plants from insects. They consequently get settled into soil particles, when used on plants.
Groundwater: Through irrigation in the fields, these pesticides present in soil pass into lower layers of soil and reach ground water.

Question. List two environment friendly practices or habits which need to be followed by every member of a family or community. Explain how these practices will support the “save the environment” mission.
Answer. The below practices will support “Save the environment mission”
a. Use of paper bags or jute bags instead of plastic bags
b. Segregate biodegradable and non-biodegradable wastes in separate dustbins.
c. Use fuels like CNG, unleaded petrol or other ecofriendly fuels in vehicles. Due to uses of environment friendly practices or habits we can save our environment

Question.  What are the by-products of fertilizer industries? How do they affect the environment?
Answer. The harmful by-products of fertiliser industries are the harmful gases like sulphur dioxide and Nitrogen oxides. They cause air pollution and combine with the water vapour in the atmosphere to cause harmful acid rain

Question. Make a diagrammatic representation showing various trophic levels.

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. Look at the following figures. Choose the correct one and give reason for your choice.


Answer: Fig. “A” is correct.
• In an ecosystem, the number of individuals at producer level is maximum. This number reduces at each successive level. Therefore, the shape is a pyramid with broader base and tapering apex.
• On an average 10% of the food changes into body mass and is available for the next level of consumers 

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. List two main components of an ecosystem.
Answer: Two main components of an ecosystem are
(1) Biotic Component
(2) Abiotic component  

Question. What is meant by non-biodegradable waste? Identify biodegradable waste from the following.
Empty packet of chips, empty plastic bottle of mineral water, empty paper box of sweets, empty tin of cold drink. 
Answer:  Substances that cannot be broken down into simpler substances by the action of microorganisms are called non-biodegradable. They stay in environment for years and cause pollution From the list, empty paper box of sweets is biodegradable 
Question. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why? 
Answer:   An aquarium is an artificial and incomplete ecosystem in contrast to a pond/lake which are natural, self-sustaining and complete ecosystems. Ponds and lakes have their own cleaning mechanisms because of presence of various microorganisms but Aquarium lacks decomposer microbes which convert the complex organic compounds of dead organisms into simple substances that can be reused by plants. Hence the dead fishes of the aquarium are not decomposed. so it needs regular cleaning. 

Question. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:   Ozone prevents the passage of harmful ultraviolet radiations through the atmosphere to the earth. The damage to the ozone layer is a cause of concern since in the absence of the ozone layer harmful ultraviolet radiation will reach the earth and harm organisms on the earth. Depletion of ozone layer has been linked to chloro-floro-carbons or CFCs which are used as refrigerants. To prevent depletion of the ozone layer, use of CFCs is being restricted and replaced by more eco-friendly refrigerants under a UNEP (United Nations Environment Programme) initiative agreed upon in1986.

Question. Define Ecosystem. Briefly describe the two types of ecosystem.
Answer:   Ecosystem: An Ecosystem is a self contained unit of living things (plants, animals and decomposers) and their non-living environment (soil, air and water). It needs only the input of sunlight energy for its functioning.
Types of Ecosystem: There are two types of ecosystem:
Natural ecosystem: These ecosystems operate in the nature by themselves without any human interference. They can be terrestrial or aquatic. The common examples of terrestrial ecosystem are forest, grassland and desert. The common examples of aquatic ecosystem are ponds, lakes, rivers, sea.
man-made or artificial ecosystem: These are maintained by man and hence are called Man- made ecosystems or artificial ecosystem. Man maintains the natural balance by the addition of energy and planned manipulations. Example: crop field, aquarium, garden.

Question. Differentiate between natural and artificial ecosystem.

CBSE Class 10 Science Our Environment Assignment Set B


Question. Why decomposers are necessary in environment?
Answer:. Decomposers act on all biodegradable substances and break them into simple inorganic materials and maintain the balance of materials in the ecosystem and cleanse the environment. 

Question. Give one example of grassland ecosystem and one example of pond ecosystem.
Answer: Grass land Ecosystem: Grass → grasshopper → frog → snake → peacock.
Pond Ecosystem : Blue-green algae → small fish → big fish → birds

Question. State different types of consumers in an ecosystem.
Answer:  The consumers are herbivores, carnivores, omnivores, parasites, saprophytes and decomposers.

Question. Define an ecosystem. Explain in detail about its various components.
Answer: Ecosystem is defined as a well defined unit or area in an environment where biotic and abiotic components interact with each other to maintain balance in nature.
Biotic components – producers, consumers, saprotrophs.
Abiotic components – air, water, sunlight.

Question. Minimum energy is available at highest trophic level while maximum energy is at lowest level. Explain.
Answer: Since non-biodegradable substances cannot be broken down into simpler forms hence they keep on accumulating in nature causing ecological imbalance.

Question. How is ozone layer important to us?
Answer: Ozone is a pollutant at lower level of atmosphere but is very useful in shielding harmful UV rays. This layer is present in the stratosphere.
In absence of ozone layer heavy damage to organism may occur e.g. skin cancer, cataract etc.

Question.  What are the problems caused by the non-biodegradable waste that we generate?
Answer: Non-biodegradable waste doesn’t decompose under the action of bacteria and other microorganisms.
• When these substances, e.g., polythene, plastics are buried under soil render that area barren and leads to soil pollution.
• These wastes don’t burn completely in presence of oxygen and release toxic gases which causes air pollution.
• The substances may be harmful on accumulating in food chain like DDT due to biomagnification.

Question.  Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment. 
Answer: Bacteria and fungi are called decomposers as they break down the dead remains and waste of organisms. They convert the organic complex substance into simple inorganic substances that go into the soil and are used up by plants.
Two advantages of decomposers:
1. They return the components back to nature and creates balance in the environment.
2. They act as cleansing agents of the atmosphere.

Question.  Why is the ozone layer getting depleted at the higher levels of the atmosphere? 
Answer: Ozone is present at higher levels of the atmosphere where CFC – Cholorofluorocarbons reach, chlorine separates and acts on O3 to split it into O2 and (O). The conditions required to do this are available at higher levels i.e., clouds and sunlight.

Question. What are the two main components of our environment? 
Answer: Biotic (living components) ⎯⎯→ Plants, animals
Abiotic (non-living components) ⎯⎯→ Water, air

Question. Why are green plants called producers? 
Answer: Green plants can prepare complex organic matter as food from simple inorganic substances like CO2, H2O in presence of sunlight and chlorophyll. They produce food and hence called producers.


Long Answers

Question. Explain some harmful effects of agricultural practices on the environment.
Answer. Harmful effects of agricultural practices on the environment are a. Change in the chemistry of soil and killing of useful microbes due to excessive use of fertilizers. b. Biological magnification occurs due to excessive use of chemical pesticides. c. Water table gets lowered due to the excess use of ground water. d. Soil fertility is lost due to extensive cropping. e. The natural ecosystems are harmed due to ploughing during agriculture.

Question. In a food chain, if 10000 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. Energy which will be available to the secondary consumer to transfer it to the tertiary consumer are
a. Energy available to producers = 10,000 Joules. Energy transfer to producer = 1% of 10,000 Joules = 100 Joules. b. According to Ten per cent law, Energy transfer to primary consumer = 10100 × 100 = 10 Joules. c. Energy transfer to secondary consumer = 10100 × 10 = 1 Joule. d. Energy transfer to tertiary consumer = 10100 × 1 = 0.1 Joule

Question. What three informations are obtained from the energy flow diagrams?
Answer: The information we get are:
(i) The energy flow is unidirectional, it flows from sun → autotrophs → herbivores → carnivores → decomposers
(ii) The flow of energy is 10% i.e., 90% of the energy is used by a given level of food chain for metabolic activities.
(iii) The unwanted chemicals like pesticides gets accumulated in the highest organism in the food chain.

Question. Explain the formation of ozone layer and its importance.
Answer: Ozone is formed when high energy ultra violet radiations split oxygen molecule into oxygen atoms. The oxygen atom combines with oxygen molecules to form a new molecules with three oxygen atoms named ozone.
CBSE Class 10 Science Our Environment Assignment Set B-3

Importance of Ozone: It is very protective when present in stratosphere it does not allow the harmful ultra violet radiations to enter the earth’s surface which can cause skin cancer in human beings.

Question. What are decomposers? How are they important for the ecosystem?
Answer: Decomposers are the organisms which act on dead organisms to decompose the body so as to release all the elements back to nature.
They act as cleansing agents, hence they are important in the ecosystem.

Question. What are food-chains and food webs? Why are smaller food chains better? What is 10% flow?
Answer: Food chain: The flow of food from sun to autotrophs, from autotrophs to herbivores and from herbivores to carnivores is called food chain. A food chain can have two levels or five to six levels also.
Food web: When an organism is eaten by two or more other kinds of organisms, instead of straight chain an interlinked chain is formed, is termed as food web.

CBSE Class 10 Science Our Environment Assignment Set B-2
Smaller the food chain the energy available for the next level of consumer in such a chain is more. As the loss of energy at each step takes place and very little energy is left after four trophic levels.
The green plants in terrestrial ecosystem capture about 1% of the sun’s energy and convert it into food energy. When green plants are eaten by primary consumers—a great deal of energy is lost for the life processes and only 10% of the energy is available for the next level of consumers.

Question. Distinguish between biodegradable and non-biodegradable substances. List two effects of each of them on our environment. 

CBSE Class 10 Science Our Environment Assignment Set B-1


Question. Why is improper disposal of waste a curse to environment? 
Answer:   Disposal of waste means getting rid of waste. Improper disposal of waste can cause significant harm to human health, safety and can develop causing serious environmental problems.
(1) The accumulation of biodegradable wastes causes an obnoxious smell, which is created during the process of decomposition.
(2) There can also be a possibility of sparking an epidemic if the waste is dumped near a residential area or is allowed to contaminate the water bodies. People living in areas near old and abandoned waste disposal sites are in a particularly vulnerable position.
(3) Improper waste storage or disposal frequently contaminates surface and groundwater supplies. In case of non- biodegradable substances, for example, chemical fertilizers, the nutrients in the soil are destroyed which thus affects health and reduces the longevity of the people who consume the food cooked with the produce grown in such a soil.
(4) Improper disposal of plastics prevents the seepage of rainwater underground and lead to water scarcity.
(5) If the waste is not properly segregated at some place, it might not biodegrade and simply persist in the environment for a long time or may harm the various members of the ecosystem. 

Question. (A) Create a food chain of the following organisms: Insect, Hawk, Grass, Snake, Frog
(B) Name the organism at the third trophic level of the created food chain.
(C) Which organism of this food chain will have the highest concentration of non- biodegradable chemicals?
(D) Name the phenomenon associated with it. (E) If 10,000 joules of energy is available to frogs, how much energy will be available to snakes in this food chain.
Answer:   (A) Food chain Grass → Insect → Frog → Snake → Hawk
(B) The organism at the third trophic level of the created food chain is frog.
(C) The organism which will have the highest concentration of non-biodegradable chemicals is Hawk.
(D) The phenomenon associated with it is Biological Magnification.
(E) If 10,000 joules of energy is available to frogs, 1000 joules of energy will be available to snakes in this food chain as per 10% law of energy.

Question. i. How do food chains get shortened? How does the shortening of food chain affect the biosphere?
ii. How will you justify that vegetarian food habits give us more calories? 
Answer:  i. Undesirable activities of man eliminate the growth of organisms belonging to one or more trophic levels in a food chain. Thus, Food chains gets shortened.
For example:
i. Hunting tigers for their skin
ii. Plants →Deer →Tiger
iii. Deforestation
If man cuts down the trees for their commercial needs then deers which are dependent on trees get less food and also less amount of oxygen will released in the atmosphere where all living organism are dependent on O2. If deers become less in number due to lack of food, tiger become less in number . Thus the indirect activities of human beings leads to imbalance in ecosystem and biosphere. If organisms of one trophic level are eliminated, the organisms prior to that trophic level will flourish and increase in number and also the organisms of the subsequent trophic level will sharply decrease, therby creating an imbalance.
ii. Vegetarian food chain is advantageous in terms of energy because it has less number of trophic levels. As we know, only 10% of the energy is transferred to the next trophic level in a food chain, so if a person is vegetarian then, he would have maximum amount of energy by consuming producers or plants in a food chain.
Vegetarian food chain gives ten times more energy than the non-vegetarian food chain.
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