CBSE Class 10 Science Our Environment Assignment Set C

Read and download free pdf of CBSE Class 10 Science Biology Our Environment Assignment. Get printable school Assignments for Class 10 Science. Standard 10 students should practise questions and answers given here for Chapter 15 Our Environment Science in Grade 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 standard 10. This test paper with questions and answers for Grade 10 Science will be very useful for exams and help you to score good marks

Chapter 15 Our Environment Class 10 Science Assignment

Question : Ozone depletion has resulted in: 
a. More UV radiations on earth
b. Warming of earth
c. Decrease in temperature
d. Less UV radiations on earth
Answer :  A
Question : Which of the following constitutes the fourth trophic level? 
a. Small carnivores
b. Top carnivores
c. Plants
d. Herbivores
Answer :  B
Question : Micro-organisms belong to the group of: 
a. Decomposers
b. Consumers
c. None of the above
d. Producers
Answer :  A 

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

Answer : (a) specific (b) producers (c) food chain (d) ecology (e) non-biodegradable ; biodegradable


1. Read the following and answer the questions :

The belief the Ganga River is "holy" has not, however, prevented over-use, abuse and pollution of the river. All the towns along its length contribute to the pollution load. It has been assessed that more than 80 per cent of the total pollution load (in terms of organic pollution expressed as biochemical oxygen demand (BOD)) arises from domestic sources, i.e., from the settlements along the river course. Due to over-abstraction of water for irrigation in the upper regions of the river, the dry weather flow has been reduced to a trickle. Rampant deforestation in the last few decades, resulting in topsoil erosion in the catchment area, has increased silt deposits which, in turn, raise the river bed and lead to devastating floods in the rainy season and stagnant flow in the dry season. Along the main river course there are 25 towns with a population of more than 100,000 and about another 23 towns with populations above 50,000. In addition, there are 50 smaller towns with populations above 20,000. There are also about 100 identified major industries located directly on the river, of which 68 are considered as grossly polluting. Fifty-five of these industrial units have complied with the regulations and installed effluent treatment plants (ETPs) and legal proceedings are in progress for the remaining units. The natural assimilative capacity of the river is severely stressed. The principal sources of pollution of the Ganga River can be characterized as follows:

Question. Accumulation of toxic substances at higher trophic levels of an ecosystem through the food chain in water bodies affects which of the following organisms more?
(a) Phytoplankton
(b) Zooplankton
(c) Small fishes
(d) Large fishes
Answer: D

Question. When toxic chemicals and nutrients get deposited in the water bodies, which of the following gases get depleted in the water bodies?
(a) Oxygen
(b) Carbon dioxide
(c) Both oxygen and carbon dioxide
(d) Nitrogen
Answer: C

Question. Which of the following activities may pollute the river water more?
(a) Bathing using detergent and soap
(b) Discharging animals excreta
(c) Deposit flowers and leaves as the part of puja
(d) Bathing without soap and detergent
Answer: A

Question. Which of the following organisms grow abundant in water when the water get mixed with nutrients like sulphates, phosphates etc.?
(a) Algae
(b) Zooplankton
(c) Small fishes
(d) Large fishes
Answer: A

Question. Green Algae and Diatoms are the major producers of Aquatic ecosystem .Which of the following will be more in the aquatic ecosystem:
(a) Small fishes
(b) Large fishes
(c) Algae and phytoplankton
(d) Tadpole
Answer: A


Q.2. Read the following and answer the questions :

The atmosphere is a blanket of air and a precious natural resource for sustaining life on the Earth. Unfortunately, human activities based on national/personal interests are causing harm to this common resource, notably by depleting the fragile ozone layer, which acts as a protective shield for life on the Earth. Ozone molecules consist of three oxygen atoms, Ozone molecules are exceeding rare: fewer than ten in every million molecules of air. However, for nearly a billion years, their presence in the atmosphere has played a vital role in safeguarding life on Earth. The ozone in the troposphere (up to 110 kilometres above the Earth's surface) is 'bad' ozone which can damage lung tissues and plants. But about 90 per cent of ozone found in the stratosphere (between 10 and 40 kilometres above the Earth's surface) is "good" ozone which plays a beneficial role by absorbing dangerous ultraviolet (UV-B) radiations from the Sun. Without this beneficial ozone layer, humans would be more susceptible to certain diseases due to the increased incidence of ultraviolet rays from the Sun.

Question. Ozone molecules consists of:
(a) Three oxygen atoms only
(b) two oxygen atoms only
(c) Only one atom of oxygen
(d) None of the above
Answer: A

Question. Depletion of ozone layer is mainly due to
(a) Use of CFC’s
(b) Use of halogens
(c) Both (a) and (b)
(d) None of the above
Answer: C

Question. U-V rays can cause diseases in humans like
(a) Skin cancer only
(b) Cataract only
(c) Lung cancer
(d) Both (a) and (b)
Answer: D

Question. Ozone holes are more pronounced at the :
(a) Equator
(b) Tropic of cancer
(c) Tropic of Capricorn
(d) Poles
Answer: D

Question. Which of the following is an ozone depleting substance?
(a) Sulphur dioxide
(b) Methyl chloride
(c) Carbon dioxide
(d) Methane
Answer: B

3. Read the following and answer the questions :

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. Because 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, thaus showing that some life may not require solar energy to thrive.

CBSE Class 10 Science Biology Our Environment
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) 10,000 J
(b) 100 J
(c) 1000 J
(d) It will depend on the type of the terrestrial plant
Answer: B

Question. Mr. X is eating curd/yogurt. 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. The decomposers are not included in the food chain. The correct reason for the same is because decomposers:
(a) Act at every trophic level of 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

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

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

4. Read the following and answer the questions :

Observe the food web and answer the Questions given below :
CBSE Class 10 Science Biology Our Environment

Question. The mussel can be described as:-
(a) Producer
(b) Primary consumer
(c) Secondary consumer
(d) Decomposer
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 – mold, yeast and mushrooms
Answer: D

Question.3 The given figure best represents:
CBSE Class 10 Science Biology Our Environment

(a) Grass food chain
(b) Parasitic food chain
(c) Forest food chain
(d) Aquatic food chain
Answer: A

Question. In the food web, what two organisms are competing for food?
(a) A and B
(b) A and C
(c) D and F
(d) B and D
Answer: D

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

5. Read the following and answer the questions :
Study the image given below and answer the following questions.

CBSE Class 10 Science Biology Our Environment

Question. The ecosystem consists of
(a) Biotic components only

(b) Abiotic components only
(c) Both biotic and abiotic components
(d) None of the above
Answer: C

Question. Which among the following are the Primary Producers?
(a) Algae
(b) Phytoplankton
(c) Algae and phytoplankton
(d) Green plants
Answer: C

Question. Which group of organisms may have higher Bio-magnification?
(a) Producers
(b) Primary consumers
(c) Secondary Consumer
(d) Tertiary consumers
Answer: D

Question. Which is the Primary source of energy in an ecosystem?
(a) Soil
(b) Water
(c) Sun
(d) Carbon dioxide
Answer: C

Question. The image given above is an example of
(a) Aquatic ecosystem
(b) Terrestrial ecosystem
(c) Land ecosystem
(d) Natural aquatic ecosystem
Answer: D

Very Short Answer Type Questions

Question. What is the full form of CFCs and UNEP?
Answer: CFC=Chlorofluorocarbons UNEP = United Nations Environment Programme

Question. Construct an aquatic food chain showing four trophic levels.
Answer: Phytoplankton → Zooplankton → Small fish → Bird.

Question. List two causes of depletion of ozone layer
Answer: Two causes of depletion of ozone layer are as follows:
a. Use of CFC’s b. Use of Halogens

Question. Why are crop fields known as artificial ecosystems?
Answer: Crop fields are man made and some biotic and abiotic components are manipulated by humans

Question. What are decomposers? Give two examples.
Answer: Decomposers are organisms that live on dead and decaying matter. They convert complex organic material into simple materials and mix with soil. Eg: fungi, bacteria.

Question. What percentage of the solar energy is trapped and utilised by the plants ?
Answer : One per cent

Question. What percentage of energy available at the producer level is transferred at successive trophic levels in a food chain ?
Answer : Ten per cent

Question. Name two waste materials which can be recycled.
Answer : Paper and Plastics

Question. Name the process by which the volume of solid wastes can be reduced.
Answer : Landfill is the process by which the volume of solid wastes can be reduced.

Question. If 5 joules of energy is available at producer level (plants), then how much energy will be transferred to the lion in the following food chain ?
Plants → Goat → Lion
Answer : 0.05 J

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

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

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

Question. Which radiations are absorbed by ozone layer ?
Answer : Ozone absorbs UV-B radiation from the sun. When an ozone molecule absorbs UV-B, it comes apart into an oxygen molecule (O2) and a separate oxygen atom (O).

Question. Name the group of chemical compounds which damages the ozone layer.
Answer : Chlorofluorocarbons. Chlorofluorocarbons (CFCs) were widely used as refrigerants until the 1980s when it was confirmed that they were the main source of harm to the ozone layer.

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

Question. Where does all the energy in living organisms originate from ?
Answer : Sun

Question. Why are there rarely more than five links (or five organisms) in a food chain ?
Answer : There are rarely more than five links (or five organisms) in a food chain because, according to the 10 per cent law, only 10 per cent of the available energy is transferred to the next trophic level.

Question. Name two predators of snakes in a food web operating in a forest ecosystem.
Answer : Peacock and Hawk

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

Short Answer Type Questions

Question. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adapt to dispose non-biodegradable waste for saving the environment.
Answer: A. Biodegradable substances: Substances that can be slowly destroyed and broken down into very small parts by natural processes i.e., by bacteria, fungi, etc. For example, organic wastes like vegetables and fruit peels.
B. Non-biodegradable substances: Substances that cannot be broken down or decomposed into the soil by natural agents are called as nonbiodegradable.For example, plastic. a. Segregating and treating the non-biodegradable waste before putting in dustbins. b. Recycle the plastics or glass present in non-biodegradable wastes. c. Motivate people to use paper or jute bags instead of plastic bags.

Question. How is ozone formed in the higher level of the atmosphere? “Damage to ozone layer is a cause of concern”. Justify this statement.
Answer: Ozone is formed due to action of UV rays on oxygen molecules to form free oxygen atom which subsequently combines with another molecule of oxygen to form ozone. The reaction is: O + O2
→ O3 (Ozone) Ozone depletion is a cause of concern because it protects us from the harmful ultraviolet radiations of the Sun by absorbing them. The UV rays can cause skin cancer, ageing,cataract, etc. to human beings if they are not absorbed by ozone due to ozone depletion.

Question. Explain phenomenon of “biological magnification”. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?
Answer: The levels of harmful toxicants/pesticides like DDT get increased at successive trophic levels as they are neither metabolized nor excreted by the organism. They get accumulated in organism’s body with their higher concentrations at higher trophic levels. This is called as biological magnification Since, the tertiary consumers are at the top of the food chain, so a higher amount of these toxicants is present in them compared to the lower trophic levels

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. Food web increases the stability of an ecosystem. Justify.
Answer: Food web shows food relationship in an ecological community. It consists of many food chains.
Thus, if any one organism becomes endangered or extinct, the one dependent in it has an alternative option available to him for survival. In this way food web increases stability in the ecosystem

Question. Explain the terms ‘producer’ and ‘consumer’. Give two examples of producers and two of consumers.
Answer : Producers are organisms that can prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight energy in the presence of chlorophyll.
Example – Green plants and certain blue-green algae
Consumers are those organisms that consume food (eat food) prepared by producers.
Example – Lion and Tiger.

Question. (a) Define decomposers. Name one decomposer.
(b) What is the role of decomposers in the ecosystem ?
Answer : (a) Micro-organisms that break down the complex organic compounds present in dead plants and animals and their products, such as feces and urine, into simpler substances, are called decomposers. Bacteria are decomposers.
(b) Decomposers decompose dead plants and animals and keep the environment clean and fresh.

Question. What is meant by a primary consumer, secondary consumer and a tertiary consumer ? Give one example of each.
Answer : Insects (Primary consumers)⟶ Frogs(Secondary consumers)⟶ Birds(Tertiary consumers)

Question. Give an example of a four step food chain operating in grassland. Name the secondary consumer in this food chain.
Answer : Grass is the producer. Deer is the primary consumer. Wolf is the secondary consumer. Lion is the carnivore.2

Question. (a) Define trophic level. Draw the food chain with four trophic levels.
(b) What will happen if we kill all the organisms in one trophic level ?
Answer : (a) The various steps in a food chain at which the transfer of food and energy takes place are known as trophic levels.
A food chain with four trophic levels can be shown as follows.
Grass → Insect → Frog → Eagle
(b) If we kill all the organisms in one trophic level, there will be no food for the organisms of the next trophic level, and they will die of starvation. Also, the organisms of the previous trophic levels will increase in number as there will be no organism to consume them as food.

Question. What is the difference between the food habits of organisms belonging to the first and the third trophic levels ? Give one example each of the organisms belonging to these two trophic levels.
Answer : First trophic level : Autotrophs like green plants ; Third trophic level : Carnivores like frog

Question. Can the organisms of any trophic level be removed without causing any damage to the ecosystem ? Will the impact of removing all the organisms in a trophic level be different for different trophic levels ?
Answer : No, the organisms of any trophic level cannot be removed without causing any damage to the ecosystem. It will disturb the food web and will create ecological imbalance.

Question. Consider the food chain :
Grass → Deer → Lion
What will happen if all the lions are removed from the above food chain ?
Answer : If all the lions from the given food chain are removed, the population of deer will increase exponentially. Thus, deers and other plant-eaters will be present in abundance which will lead to overgrazing of grass and no grass will left. And if no grass will be left, then deer will automatically die which will eventually destroy the complete food chain.

Question. The number of malaria patients in a village increased tremendously when large number of frogs were exported from the village. What could be the cause for it ?
Answer : Frogs eat up moquitoes. In the absence of frogs, the number of mosquitoes increased too much. Mosquitoes spread malaria

Question. How does a biodegradable waste differ from a non-biodegradable waste ? Give two examples of nonbiodegradable wastes which pollute our environment.
Answer : Biodegradable waste - Waste materials that can be broken down into non-poisonous substances in due course of time, by the action of natural micro-organisms such as certain bacteria, are called biodegradable wastes. Examples: Paper and vegetable peels.
Non-biodegradable waste - Waste materials that cannot be broken down into non-poisonous or harmless substances naturally are called non-biodegradable wastes. Examples: Plastic and iron nails.

Question. Which of the following are biodegradable and which non-biodegradable ? Glass bottle, Paper, Ball point pen refill, Hay, DDT, Wheat, Cake, Wood, Polythene bag, Jute bag, Cotton cloth, Grass, Vegetable peels
Answer : Those waste materials which can be broken down to non-poisonous substances in nature by the action of microorganisms (like bacteria) are called biodegradable wastes.
Paper, hay, wheat, cake, wood, jute bag, cotton cloth, grass, vegetable peels.
Non-Biodegradable Wastes: Those waste materials which cannot be broken down into non-poisonous substances in nature are called non-biodegradable wastes.
Glass bottle, ballpoint pen refill, DDT, polythene bag. 

Question. (a) Describe an activity to show that while paper is biodegradable but plastic (say, polythene) is nonbiodegradable.
(b) Explain why, some materials are biodegradable but some are non-biodegradable.
Answer : (a) An activity to prove that paper is biodegradable and plastic is non-biodegradable is described below.
1) Take a piece of paper and a polythene bag.
2) Dig a hole in the ground about 15 cm deep and place both the paper and the polythene bag separately in it. Cover them with soil.
3) Leave them for about one month.
4) On uncovering the buried materials, it will be observed that the paper has been partially eaten up by micro-organisms, whereas the polythene bag has remained unaffected. This proves that paper is biodegradable, whereas plastic is non-biodegradable.
(b) Some materials are biodegradable, whereas some are non-biodegradable because decomposers break down natural materials such as paper but do not break down man-made materials such as plastics. Non-biodegradable materials consist of compounds that are not degraded by decomposers, and they persist in the environment.

Question. Write down a food chain :
(a) in the sea
(b) which ends with humans
(c) with five links in it.
Answer : a) Food Chain in the sea:
Plankton →Small fish → Large fish→ Shark
(b) Food Chain which ends with humans.
Grass → Goat → Man
(c) Food Chain with five links in it.
Grass → Insects → Frog → Snake → Eagle

Question. At which trophic level a person is feeding when he is eating :
(a) roasted chicken (b) bread (c) eggs (d) apple (e) fish
Answer : (a) 3rd trophic level (b) 2nd trophic level (c) 3rd trophic level (d) 2nd trophic level (e) 4th trophic level

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

Question. Construct (a) a long food chain, and (b) a short foodchain, ending with man.
Answer :a) Algae → Protozoa → Small fish → Big fish → Man (b) Plants → Man

Question. (a) State one advantage of using jute bags over plastic bags for shopping.
(b) Write a common food chain of a pond ecosystem having four links.
Answer : (a) Jute bags are biodegradable, and hence they are degraded by micro-organisms. Plastic bags are non-biodegradable, and hence they are not degraded by micro-organisms. Therefore, the advantage of using jute bags over plastic bags is that jute bags are environment friendly.
(b) Algae → Protozoa → Small fish → Big fish

Question. We do not clean ponds or lakes but an aquarium needs to be cleaned periodically. Why ?
Answer : Pond is a complete ecosystem having decomposer organisms which are the cleansing agents themselves. Aquarium is a sort of incomplete ecosystem in the sense that it does not have decomposer organisms for cleansing purposes.

Question. What will be the consequence of the absence of decomposers in the ecosystem ?
Answer : If there were no decomposers in the ecosystem, then dead plants and animals would remain as such, and their elements would never be returned to the soil, air and water.

Question. Give two differences between food chain and food web.
Answer :(i) A food chain contains a few organisms feeding on one another whereas a food web contains a large number of organisms in the form of interconnected food chains (ii) In a food chain, the organism at higher trophic levels feeds only upon a single organism of the lower trophic level but in a food web, the organism at higher trophic levels can feed upon organisms of lower trophic levels of many food chains .

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

Question : Rearrange the following according to their trophic levels in a food chain. Fish, zooplankton, seal, phytoplankton.
Answer :  A food chain always start with producers followed by primary, secondary and tertiary consumer thus, the food chain will be Phytoplankton, zooplankton, fish, seal.
Question : Discuss the transfer of energy from sun to carnivores. 
Answer :  The solar energy is trapped by plants (producers) in the form of carbohydrates. It flows in the food chain from herbivores to carnivores and at each level is utilized as mechanical energy. It is also lost as heat into atmosphere. Almost 90% of energy is used up at each trophic level and only 10% is transferred to next level. 
Question : Suggest any two methods for reducing the problem of waste disposal. 
Answer :  The amount of waste for disposal can be reduced by:
a. Separation of biodegradable and non-biodegradable waste at source.
b. Decomposing the bio degradable waste & producing manure or bio-gas from it.
c. Recycling non biodegradable waste like plastic, metal cans etc. 
Question : Mention the form of energy transfer, if a grasshopper is eaten by a frog. 
Answer : In a food chain, if a grasshopper is eaten by a frog, then the energy transfer will be between primary consumer and secondary consumer. Grasshopper feeds on producers, i.e. the grass and plants which starts the food chain. So, it occupies the level of primary consumer and stores energy in the form of biomass which is taken up by frog by eating grasshopper thus frog becomes the secondary consumer. 
Question : Explain the concept of food chain. 
Answer :  Food chain: A food chain consists of a connected group of producers, consumers and decomposers. It starts with energy from the sun and nutrients from the soil. They pass through a plant and one or several consumers to final consumer that is not fed upon by other. Even then one may have parasites, and in time it will certainly die. The food relation in simplest from grass-deer-tiger-micro-organisms representing a producer, primary consumer, a secondary consumer and decomposer is called a food chain. A common example of food chain is that involving the plants and grazing antelopes. The plants are producers and the antelope being herbivorous are primary consumers. The antelopes in turn are consumed as food by carnivorous animals, such as lion and cheetah. They constitute a group called secondary consumer. They eat upto their fill but do not completely consume the antelopes. The tertiary consumers, the scavenging vultures, then feed on the remains. After they finish, the bones may be crushed by jackals and hyenas. Still there is sufficient nutrient to attract a large number of  insects. Finally whatever is left may be decomposed by bacteria and fungi, thus return the simple components to soil. The last group constitute the decomposers. Green plants are the producers, mouse is the primary consumer and kite is tertiary consumer. Thus a food chain is set up. 

Long Answer Type Questions

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. Suggest any four activities in daily life which are eco-friendly.
Answer: The eco-friendly activities in life are
a. Planting of trees
b. Segregating biodegradable and non-biodegradable wastes
c. Using cloth bags, jute bags or paper bags instead of plastic bags
d. Creating awareness on environment protection through initiatives and campaigns e. Using of manures and organic agricultural methods Using less of chemical fertilizers and pesticides f.Controlling pollution by using fuels like CNG.

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: Because the energy moves progressively through the various trophic levels and is no longer available to the previous trophic level. The energy captured by autotrophs does not revert to the solar input.
a. Pesticides, used for crop protection when washed down into the soil/ water body, are absorbed by the plant along with water and minerals
b. Plants are consumed by animals and these chemicals get into animal body
c. Being non-biodegradable, these chemicals get accumulated progressively in the food chain and into our body
d. As we go into higher levels of food chain amount of harmful substances will increase in the body of organisms as a result of biomagnification

Question. (a) In the following food chain, 5 J of energy is available to man. How much energy was available at the producer level? Plants→Sheep→Man
(b) Explain phenomenon of “biological magnification”. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?
Answer: (a) By 10% energy law the required energy available at the producer level was 500 Joules.
(b) The levels of harmful toxicants/pesticides like DDT get increased at successive trophic levels as they are neither metabolized nor excreted by the organism. They get accumulated in organism’s body with their higher concentrations at higher trophic levels. This is called as biological magnification Since, the tertiary consumers are at the top of the food chain, so a higher amount of these toxicants is present in them compared to the lower trophic levels

Question. (a) With the help of a flow diagram, describe how energy from the sun flows through various trophic levels.
(b) Explain why, the flow of energy in the ecosystem is said to be unidirectional.
Answer : (a) Energy from the sun flows through various trophic levels in the following steps.
1) Green plants trap solar energy with the help of their green pigment, chlorophyll, and convert it into chemical energy. They store this energy in the form of carbohydrates. On an average, about one per cent of the sun's energy falling on the leaves of green plants is used by the plants in the process of photosynthesis and stored as the chemical energy of food.
2) When plants are eaten by herbivores, the chemical energy stored in the plants is transferred to them.
3) The herbivores are then consumed by carnivores, and the chemical energy stored in the flesh of the herbivores is transferred to the carnivores.
4) Some of the energy from producers and consumers is also utilised for the life processes of micro-organisms called decomposers. Decomposers, in turn, release the unutilised energy into the environment as heat. The energy that is not utilised by producers, consumers and decomposers is lost in the environment as heat. This heat is called community heat.
(b) Energy enters plants from the sun during food production through photosynthesis. This energy is then passed on from one organism to another in a food chain. The energy given out by organisms as heat is lost in the environment and does not return to be used by plants again. This makes the flow of energy in an ecosystem unidirectional. Thus, the flow of energy in an ecosystem is said to be unidirectional because the energy lost as heat from the organisms in a food chain cannot be reused by plants in photosynthesis

Question. (a) What is ozone ? How is it formed ?
(b) How does ozone layer protect us from harmful effects in the environment ?
(c) What is UNEP ? What step has been taken by UNEP in 1987 to prevent too much damage to the ozone layer ?
Answer : (a) Ozone is made up of three atoms of oxygen combined together. It is formed high up in the atmosphere by the action of ultraviolet (UV) radiation on oxygen gas. The UV radiation from the sun splits the oxygen gas into free oxygen atoms.
(b) The ozone layer protects us from the harmful effects of the UV radiation from the sun by absorbing it and preventing it from reaching the earth's surface
(c) The UNEP is United Nations Environment Programme. In 1987, in an attempt to protect the ozone layer, the UNEP forged an agreement among its member countries to freeze the production of chlorofluorocarbons at 1986 levels.

Question. (a) How is energy introduced into the ecosystem ?
(b) Consider the following food chains :
(i) Plants → Mice → Snakes → Hawks
(ii) Plants → Mice → Hawks
If energy available at the producer level in both the food chains is 100 J, in which case will hawks get more energy as food and by how much ? Justify your answer.
Answer : (b) Second case ; 0.9 J

Question. (a) Explain why, a food chain usually cannot have more than three or four steps.
(b) Calculate the amount of energy that will be available to big fish in the following food chain, if 10,000 J of energy is available to small algae from the sun :
Small algae → Zooplankton → Fish → Big fish
Answer : (b) 0.1 J

Question. (a) Name and state the law given by Lindeman which tells us how much energy entering a particular trophic level of organisms is available for trasnsfer to the next higher trophic level.
(b) How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 10,000 J of energy is available to paddy from the sun ?
Answer :(b) 0.1 J

Questions Based on High Order Thinking Skills (HOTS)

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

Question. The following is a food chain that ends with human : plants → bee → human
(a) Explain how plants provide food for bees.
(b) How do bees provide food for humans ?
(c) How does this food chain differ from a usual food chain involving human such as : plants → goat → human ?
(d) Do you think that the food chain given in this question can really be regarded as a food chain ? Explain your answer.
Answer : (a) Bees suck nectar from flowers of plants (b) Bees provide honey as food (c) In this food chain, human eats the product obtained (honey) from bees, he does not eat the bees directly. On the other hand, in the food chain, plants → goat → human, the human eats the meat of goat directly (d) No. 
Because the human does not obtain food by eating the bees directly.

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

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

Question. What would happen to the number of rabbits and grass plants if the number of foxes :
(a) increased ?
(b) decreased ?
Answer : (a) If the number of foxes increases, it will lead to foxes consuming more rabbits as food, which will lead to a decrease in the number of rabbits. Hence, grass plants will grow denser as there will be fewer rabbits to consume them.
(b) If the number of foxes decreases, then there will be fewer foxes to consume rabbits as food, so the number of rabbits will increase, which will, in turn, lead to rabbits consuming more grass plants as food. Hence, grass plants will become sparser.

Question. What would happen to the number of grass plants and foxes if the number of rabbits :
(a) increased ?
(b) decreased ?
Answer : (a) If the number of foxes increases, it will lead to foxes consuming more rabbits as food, which will lead to a decrease in the number of rabbits. Hence, grass plants will grow denser as there will be fewer rabbits to consume them.
(b) If the number of foxes decreases, then there will be fewer foxes to consume rabbits as food, so the number of rabbits will increase, which will, in turn, lead to rabbits consuming more grass plants as food. Hence, grass plants will become sparser.


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

Questions Based on High Order Thinking Skills (HOTS)

Question. The gas A is used by most of the animals to obtain energy from food by the process of respiration. When A is acted upon by radiation X, it gets converted into another gas B which is an allotrope of A but poisonous when inhaled. B forms a kind of layer C in the upper atmosphere which absorbs radiations X coming from a source Y and prevent them from reaching the earth. Some chemicals Z released from the various devices on the earth are destroying the layer C slowly. In fact, a hole has already been formed in layer C over the area D of the earth.
(a) What are gases (i) A, and (ii) B ? Write their molecular formulae.
(b) Name the layer C.
(c) What are (i) X, (ii) Y, and (iii) Z ?
(d) Name the area D.
(e) Name any two human ailments which may be caused by X.
Answer : (a) (i) Oxygen, O2 (ii) Ozone, O3 (b) Ozone layer (c) (i) Ultraviolet radiations (ii) Sun (iii) Chlorofluorocarbons (CFCs) (d) Antarctica (e) Skin cancer ; Cataract

Question. The surface of water in a lake appears green due to a layer of tiny free-floating organisms X on its surface.
The lake water also contains organisms like water beetle, fish and tadpole. The sun shines over the lake water and provides energy for the functioning of this lake ecosystem.
(a) What could organisms X be ?
(b) Write a food chain comprising of all the four organisms mentioned.
(c) What is the general name of the food chains like the one written above ?
(d) Name (i) secondary consumer (ii) producer (iii) tertiary consumer, and (iv) primary consumer, in the above food chain.
(e) If the tertiary consumer gets 0.2 J of energy from the secondary consumer, then how much energy was radiated by the sun to the producer ?
Answer : (a) Algae (b) Algae →
Tadpole → Water beetle → Fish (c) Aquatic food chains (d) (i) Water beetle(ii) Algae (iii) Fish
(iv) Tadpole (e) 20000 J

Question. A forest ecosystem having a lot of green plants has some foxes, lions and rabbits in it.
(a) Write a food chain comprising all the four organisms mentioned above.
(b) Name (i) one herbivore, and (ii) two carnivores, in this food chain.
(c) Name the link which is a predator as well as a prey.
(d) Name (i) second trophic level, and (ii) third trophic level.
(e) Which link of this food chain can feed on second trophic level as well as third trophic level, independently ?
(f) If the sun provides 1000 J of energy to the plants, then how much energy will be transferred to fox through the food chain.
Answer : (a) Green plants → Rabbit → Fox → Lion (b) (i) Rabbit
(ii) Fox and Lion (c) Fox (d) (i) Rabbit (ii) Fox (e) Lion (f) 0.1 J

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

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


Notes Our Environment Class 10 Science


Environment is everything that is around us. Various factors in the environment interact with each other and affect the environment .Similarly; human activities also have affected the environment. The changed taking place in environment because of this are in fact affecting of life.
What happen when we add our waste to the environment?
All human made waste is not naturally treated by nature. Certain man-made materials like plastic persist in nature for a very long time. This is because neither organisms can break it down nor physical-processes like heat and Pressure are enough for its decomposition. Based on this waste is categorized broadly into two groups.
Substances that break down by biological processes are called biodegradable. Substances that do not break down by biodegradable processes are called non-biodegradable.
Ecosystem: What are its components?
Ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, Wind, soil, and minerals. All living organisms interact with each other and their growth reproduction and other activities are influenced by abiotic factors of the ecosystem. Some ecosystems are natural while some are manmade.
Food chains and food webs
Each step of the food chain forms a trophic level. Autotrophs or producers are at the first trophic level in every food chain. They convert the solar energy into chemical energy. Rest all the organism is dependent on plants for food directly or indirectly. Herbivores are plant eating organisms. They are primary consumers and present at the second trophic level. Carnivores survive on herbivores. They are secondary consumers. They acquire position in the food chain at third trophic level. At fourth trophic level, larger carnivores are present. They survive on either herbivores or other carnivores. At the end decomposers decompose dead organisms and again they are made available to the plants through soil and water. Food web is series of branching food chains where different food chains are interconnected.
Flow of energy
Energy obtained by plants from the sun is hardly 1% of sunlight available to them. Energy passed on to the every next trophic level is 10% of the energy acquired by previous trophic level. Hence, lesser and lesser energy is made available as we go along the food chain. Flow of energy within food chains form a pattern which can be described as a pyramid which is broader at the base with producers being at 1st trophic level and narrower at the top with tertiary consumers or fourth trophic level.
Biological Magnification
It is a process where harmful chemicals from different sources get introduced into the food chain and their concentration gets magnified as they move to the next trophic level. As human is at the top in every food chain, maximum concentration of these chemicals can be found in human bodies. These chemical are not degradable so they stay until the end.
How do our activities affect the environment?
Our activities affect the environment by creating various problems. Couples of them that are quite serious now are depletion of ozone and waste management.
Depletion of ozone Layer
Presence of ozone (O3) in the atmosphere is essential as well as poisonous. On the surface of the earth, it may be harmful but at higher levels of the atmosphere, it is very crucial. Let shields the surface of the earth form Ultraviolet radiations of the sun. Filtering such radiations at higher levels protects us from many harmful diseases like Skin Cancer. The amount of ozone, in the atmosphere began to drop sharply in 1980s creating a hole in layer. The reason behind this less mainly linked to synthetic chemical like Chlorofluorocarbons. This is a global issue hence many Countries have taken and many are taking initiatives towards freezing CFC production.
Management of garbage we produce
Day by day maximum things that are being produced have packaging made of non-biodegradable substances. Our lifestyles not only generates high amount of waste but also uses raw materials that cannot be decomposed naturally. Management of such waste so usually called waste management. Negative effects of this on environment are pollution and loss of biodiversity. Need of the hours is to find alternatives that can reduce Adverse effects and create a sustainable life for everyone.
Chapter 01 Chemical Reactions and Equations
CBSE Class 10 Science Chemical Reactions and Equations Assignment

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