CBSE Class 10 Science Our Environment Assignment Set C

Question : Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest
Answer : A

Question : In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 5 kJ
(b) 50 kJ
(c) 500 kJ
(d) 5000 kJ
Answer : D

Question : An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects
Answer : C

Question : How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?
(a) 100%
(b) 10%
(c) 1%
(d) 0.1%
Answer : B

Question : In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form of:
(a) heat energy
(b) chemical energy
(c) mechanical energy
(d) light energy
Answer : B

Question : The decomposers in an ecosystem
(a) convert inorganic material, to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not breakdown organic compounds
Answer : B

Question : Which of the following are water intensive crops?
(a) Wheat are rice
(b) Wheat and sugarcane
(c) Sugarcane and rice
(d) Wheat and gram
Answer : A

Question : The most poisonous product formed by incomplete combustion of fossil fuels is
(a) Carbon dioxide
(b) Nitrogen dioxide
(c) Carbon monoxide
(d) Sulphur dioxide
Answer : C

Question : In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers
Answer : A

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

Fill in the following blanks with suitable words :
(a) Decomposer organisms are................in 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

CASE STUDY QUESTIONS

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.

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 :

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:

(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.

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