CBSE Class 10 Science Our Environment Assignment Set A

Read and download free pdf of CBSE Class 10 Science Our Environment Assignment Set A. 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

MCQ Questions for NCERT Class 10 Science Our Environment 

Question. _________ are biotic factors.
(a) Mountains
(b) Rocks
(c) Grass
(d) All of these
Answer: C

Question. In an ecosystem, the matter is recyclable because of
(a) decomposition activity of decomposers
(b) the sun, which is an ultimate source of energy
(c) the fact that matter is made up of atoms
(d) None of these
Answer: A

Question. ____________ are the smallest and the most important components of an ecosystem.
(a) Decomposers
(b) Viruses
(c) Algae
(d) Phytoplanktons
Answer: A

Question. In the food web, which 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. Biological magnification is defined as
(a) the accumulation of harmful chemicals at each trophic level of the food chain.
(b) the accumulation of organic matter at the first trophic level of the food chain.
(c) the reduction of energy at each trophic level of the food chain.
(d) an increase in the population of a species at each trophic level of the food chain.
Answer: A

Question. Which agricultural activites are affecting the environment?
(a) Overuse of fertlisers and pesticides
(b) Using groundwater for irrigation
(c) Extensive cropping in the same area of land
(d) All of the above
Answer: D

Question. Which set of the organisms belong to the same trophic level?
(a) Plants; phytoplanktons
(b) Rabbit; snake
(c) Deer; tiger
(d) Phytoplanktons; zooplanktons
Answer: A

Question. Pesticide can disturb the balance within the ecosystem by
(a) indiscriminately killing pests and the predators of these pests
(b) biomagnification
(c) eutrophication
(d) bioaccumulation
Answer: A

Question. If the energy at the third trophic level is 5J. What would be energy at the first trophic level?
(a) 5000 J
(b) 500J
(c) 50J
(d) 5 J
Answer: B

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. Flow of energy in an ecosystem is always:
(a) unidirectional
(b) bidirectional
(c) multidirectional
(d) no specific direction
Answer: A

Question. Which of the following is the best way for the disposable of kitchen waste?
(a) Landfill
(b) Composting
(c) Incineration
(d) Reusing
Answer: B

Question. Which of the following statements holds true for the energy flow in an ecosystem?
(a) Energy can never be transferredbidirectionally between producers to consumers.
(b) Energy flows in a unidirectional manner in an ecosystem.
(c) Only 10% of the energy is transferred from one trophoc level to the next trophic level.
(d) All of the above
Answer: D

Question. Which of the following occupies the top-most trophic level?
(a) Humans
(b) All producers
(c) All carnivores
(d) All omnivores
Answer: A

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

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

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?
(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
(a) Terrestrial ecosystem
(b) Land ecosystem
(c) Natural aquatic ecosystem
Answer. D

Question. Which of the following is biodegradable? 
(a) Polythene
(b) Paper
(c) Aluminum foil
(d) Plastic
Answer: B
Explanation: Substances that can be broken down by biological processes are said to be biodegradable. Substances like paper, wood and cloth are biodegradable.
Question. “Flow of energy is unidirectional”. It means that: 
(a) Energy which passes to the higher trophic levels doesn’t come back to lower trophic levels.
(b) The energy of the autotrophs reaches back to the solar input.
(c) None of these
(d) Energy always flows form east to west direction.
Answer:  A
Explanation: The flow of energy in an ecosystem is always unidirectional. It means that as the energy moves progressively through the various trophic levels, it is no longer available to the previous level. The energy that is captured by the autotrophs (producers) does not revert back to the solar input. The energy which passes to the herbivores (primary consumers) does not come back to the autotrophs (producers).


Question. The inter locking pattern of various food chains is referred as food web.
Answer: True

Question. An ecosystem consists of biotic and abiotic components.
Answer: True

Question. The amount of usable energy remains constant as it is passed from one trophic level to another.
Answer: False

Question. In general, food webs consist of producers, consumers, and decomposers.
Answer: True

Question. Forests, and ponds are natural ecosystem while gardens and fields are artifical ecosystem.
Answer: True

Question. The energy takes place from autotroph to the heterotrophs.
Answer: True

Question. Blue green algae are producers.
Answer: True

Question. Decomposers reduce the fertility of soil.
Answer: False

Question. The energy within an ecosystem is fixed and never changes.
Answer: False

Question. The reproduction and other activities of living organisms are affected by the abiotic components of ecosystem.
Answer: True

Question. Food ensures survival of all types of trophic levels.
Answer: True

Question. Decomposers reduce the fertility of soil.
Answer: False

Question. Rag pickers remove reusable articles.
Answer: False

Question. The materials like plastics are not acted upon by physical process.
Answer: False

Question. Human population and technology are having a destructive impact on the biosphere.
Answer: True

Question. Forests, and ponds are natural ecosystem while gardens and fields are artifical ecosystem.
Answer: True

Question. An ecosystem is made up of one type of community.
Answer: False


Assertion And Reason

DIRECTION : In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Question. Assertion : The crown fires are most destructive as they burn the tree top.
Reason : Due to crown fire the temperature of that area may rise upto 700cC.
Answer: A

Question. Assertion : Biotic components of ecosystem continuously require energy to carry on life processes.
Reason : Abiotic comonents are the non-living factors of the ecosystem.
Answer: B

Question. Assertion : Ozone is both beneficial and damaging.
Reason : Stop the release of chlorofluorocarbons to protect the ozone.
Answer: B

Question. Assertion : Ecology is study of relationship between living organisms and their environment.
Reason : The biotic community and non-living environment of an area function together to form an ecosystem.
Answer: A

Question. Assertion : Garden is an artificial ecosystem.
Reason : Biotic and abiotic components are manipulated by humans.
Answer: A

Question. Assertion : Trophic levels are formed by only plants.
Reason : Food chains and webs are formed due to linked organisms on the basis of their nutrition.
Answer: D

Question. Assertion : CFCs deplete the ozone layer.
Reason : CFCs are used as refrigerants and in fire extinguishers.
Answer: A

Question. Assertion : Green plants of the ecosystem are the transducers.
Reason : Producers trap the radiant energy of the sun and change it into chemical energy.
Answer: A

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

Question. Assertion : Herbivores are called first order consumers.
Reason : Tiger is a top carnivore.
Answer: B

Question. Assertion : Consumers are present at the first trophic level.
Reason : Consumers or heterotrophs fix energy making it available for autotrophs.
Answer: E

Question. Assertion : Aquatic food chain is the food chain present in water bodies.
Reason : The example of aquatic food chain is phytoplankton $ zooplankton $ fish $ shark.
Answer: A

Question. Assertion : Decomposers keep the environment clean.
Reason : They recycle matter by breaking down the organic remains and waste products of plants and animals.
Answer: A

Question. Assertion : Decomposers act as cleaning agents of the environment.
Reason : The decomposers recycle waste material in the hydrosphere.
Answer: C

Question. Assertion : In an ecosystem, the function of producers is to convert organic compounds into inorganic compounds.
Reason : Green plants, the producers, transduce solar energy.
Answer: A

Question. Assertion : Polythene bags and plastic containers are non-biodegradable substance.
Reason : They can be broken down by micro-organisms in natural simple harmless substances.
Answer: C




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:
• Domestic and industrial wastes. It has been estimated that about 1.4 × 106 m3 d-1 of domestic wastewater and 0.26 × 106 m3 d-1 of industrial sewage are going into the river.
• Solid garbage thrown directly into the river.
• Non-point sources of pollution from agricultural run-off containing residues of harmful pesticides and fertilizers.
• Animal carcasses and half-burned and unburned human corpses thrown into the river.
• Defecation on the banks by the low-income people.
• Mass bathing and ritualistic practices.

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

Question. Phyto plankton (60000kj) ----------→ Zooplankton (6000kj)---→Small fishes (600kj)---→Large fish(----------?????-----). Find out the energy available to large fish.
(a) 60Kj
(b) 6kj
(c) 0.6 Kj
(d) 61Kj
Answer. A

Question. The source of Primary energy source to the aquatic organisms is ---------------
(a) Algae
(b) Zooplankton
(c) Sun
(d) Moon
Answer. C

Question. The harmful metals that get mixed with the water bodies from the industrial units’ are :
(a) Iron and copper
(b) Mercury and lead
(c) Sodium and potassium
(d) Magnesium and cobalt
Answer. B

Question. The Ganga Action Plan is to --------------------
(a) Make Ganga water free from garbage
(b) Minimise the use of soap and detergents in water bodies like Ganga
(c) Make awareness among the people to save Ganga
(d) All the above
Answer. D

Question. This will be the best method to protect our River water bodies-
(a) Grow trees along the bank of Rivers
(b) Grow small fishes in River water
(c) Permitted level of sand mining
(d) Making Flats or Malls near the River
Answer. A

Very Short Answers

Question. What are the various steps of food chains through which the transfer of food energy takes place is called? 
Answer:  Trophic levels

Question. Name two natural ecosystems. 
Answer: Examples of natural ecosystems are rivers, forests, ponds, lakes and oceans.

Question. Name the organisms belonging to the second and fourth trophic levels in the food chain c1omprising the following: Frogs, Plants, Snakes, Hawks, Insects 
Answer: Plants → Insects → Frogs → Snakes → Hawks The organism belonging to the second and fourth trophic levels are insects and snakes respectively.

Question. Why do producers always occupy the first trophic level on every food chain?
Answer:  Producers always occupy the first trophic level on every food chain because only producers (green plants) have the ability to trap solar energy with the help of chlorophyll (Process known as photosynthesis).

Question. Name the gaseous components of the biosphere. 
Answer:  Carbon dioxide, oxygen and nitrogen.

Question. Monika was observing a lizard on the wall which chased an insect and ate it. She felt that the lizard was cruel and ugly. Suddenly, the lizard fell and was eaten by a cat. She started thinking, how are organisms connected to each other for their food? What is a food chain? Will the world be a better place without lizards? take a food chain of five organisms. To which trophic level does the lizard belong? 
Answer:  A lizard eats an insect. When the lizard falls, it is eaten by a cat. Hence, the lizard depends on the insect for food, while the cat depends on the lizard for food. This interdependence of organisms on one another for their food is called food chain. It is very important to have a food chain in the ecosystem for maintaining the balance of nature. Hence, even though the lizard is an ugly creature, it is important for maintaining the balance of nature. The food chain of five organisms is as follows: Sun → Plants → Insect → Lizard → Cat We can see that the lizard belongs to the fourth tropic level. 


Short Answers

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 non-biodegradable.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→ UV  O+O
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. What are decomposers? State the role of decomposers in the environment.
Answer:  The decomposers are the various organisms in the ecosystem which help in decomposing the dead bodies of plants and animals by breaking down the complex organic substances into simpler inorganic substances. Role of decomposers in the environment:
(1) They decompose the wastes of organisms, dead plants and animals in the absence of which these would pile up leading to foul gases, diseases and deaths.
(2) They help in recycling of nutrients and thus maintain fertility of the soil.
(3) They play a major role in various biogeochemical cycles which are natural ways of nutrient cycling.

Question. Why should biodegradable and non- biodegradable wastes be discarded in two different dustbins?
Answer: Biodegradable and non-biodegradable wastes should be discarded in two different dustbins because of following reasons:
(1) The biodegradable wastes kept in a separate bin can be dumped directly in a pit for composting or for dumping in landfills.
(2) The useful part of non-biodegradable wastes kept in a different bin can be separated for recycling or reusing them.
(3) Non-useful part of wastes can be disposed off in such a way that it does not harm the people or pollute the environment in anyway. 

Question. Give one example each of (1) Three step,(2) Four step and(3) Five step food chain. 



Question. How would you dispose the following wastes: 
a. Domestic wastes like vegetables peels
b. Industrial wastes like chemicals
c. Waste like plastics & metal cans
Answer:  a. Domestic wastes like vegetables peels should be disposed off in a pit & allowed to decompose to get manure.
b. Industrial wastes should be treated first to remove poisonous salts or chemicals and disposed off in water resources like river.
c. Waste like plastics & metal cans can be recycled & reused.

Question. Why are crop fields known as artificial ecosystems?
Answer:  An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. Artificial ecosystems are those ecosystems which have been modified by human beings for their own benefit. Crop fields are man made and some biotic and abiotic components are manipulated by humans.
(1) In a crop field, plants do not grow naturally. They are mostly grown by humans, hence, they are considered as artificial ecosystems.
(2) It usually consists of a major crop (monoculture).
(3) Unwanted plants are removed using weedicides.
(4) Pests and unwanted insects are killed using pesticides and insecticides.
(5) Artificial fertilisers, manures and nutrients are externally supplied to the soil by man. These activities of man alter the biotic and abiotic components of the ecosystem. Therefore, crop fields are known as artificial ecosystems.

Question. Why is plastic bag called non-biodegradable while paper is not?
 Plastic bag is not acted upon by decomposers as it cannot be broken down into simple components, so it is called non-biodegradable while paper gets decomposed.

Question. Pesticides are useful to farmers yet considered as pollutants. Give reasons.
Pesticides kill insects and pests thereby protecting the crops but these pesticides remain on the crops which enter the food chain and gets accumulated in the organisms and reaches the top most trophic level that causes diseases. When washed away by rain, it causes pollution of water.

Question. Give one advantage and one disadvantage of Ozone.
Advantage of Ozone–When it is in the stratosphere it does not allow the ultraviolet radiations to reach the earth, as UV radiations cause skin cancer and cataract.
Disadvantage of ozone: On ground level ozone is poisonous gas.

Question. Energy flow in a food chain is unidirectional. Explain.
The energy from the sun flows into autotrophs and it passes to herbivores and then to carnivores. The energy does not revert from autotrophs to the solar input or from herbivores back to autotrophs. Hence the flow is unidirectional.

Question. Differentiate between biodegradable and non biodegradable substances.
Biodegradable: These substances can be broken down by the action of saprotrophs and other agents, e.g., paper, cloth.
Non biodegradable: These substances cannot be broken down by the action of saprotrophs, e.g., glass, plastics.

Question. What is a food chain? List its characteristics features.
Food chain is defined as the phenomenon of transfer of energy through series of organisms falling on successive trophic levels.
Example: sun is the ultimate source of energy. Producers or green plants photosynthesize and utilize solar energy. Thereafter the energy is transferred to other successive levels.
Food chain can be depicted as follows:
Plants → grasshopper → frog → snake → decomposers

Question. What is biological magnification?
The accumulation of chemicals in the bodies of the organism that belongs to the top most tropic level is called biological magnification. As human beings occupy highest trophic level its maximum concentration was found in human beings only, which
resulted in neurological disorders due to damaging of CNS (Central Nervous System).

Question. What is causing the damage to ozone layer?
The CFC emission due to various industrial activities has caused damage to the Ozone layer and has contributed to global warming by allowing a major portion of UV rays to reach the earth’s atmosphere through ozone holes.

Question. Why is damage to ozone layer a cause for concern? What steps are being taken to limit this damage?
Ozone layer doesn’t allow harmful ultra violet rays of the sun to reach the earth’s surface.
In order to stop further depletion of ozone layer we must scale down the use of CFC’s in form of aerosols, refrigerants etc. and check their release in the atmosphere.
Moreover stress should be laid on using eco-friendly techniques and proper disposal of toxic material.

Question. (a) Distinguish between producers and decomposers.
(b) Classify the following as producers and decomposers.
Green plants, bacteria, fungi, blue-green algae. 

CBSE Class 10 Science Our Environment Assignment Set A

Question. Name any two abiotic components of an environment. 
Water, air.

Question. Which compounds are responsible for the depletion of ozone layer? 
Chlorofluorocarbons (CFC)

Question. Which disease is caused in human beings due to depletion of ozone layer in the atmosphere?
Skin cancer, cataract.


Long Answers

Question.  Enlist various categories of consumers giving examples of each.
The various categories of consumers are:
Herbivores — Grass eating animals, e.g., deer, rabbit.
Carnivores — Flesh eating animals, e.g., tiger, lion.
Omnivores — Animals that eat both plants and other small animals i.e., flesh e.g., crow, human being.
Parasites — Those organisms which depend on other living organisms and harm them for food, e.g., lice, tapeworm.
Saprophytes — Organisms that depend on dead and decaying matter for their food, e.g., fungi, bacteria.

Question.  Explain the interlink of biotic and abiotic factors in any ecosystem.
In an ecosystem biotic and abiotic factors are interdependent and interlinked.
For example: The grass in grassland will grow only if it gets soil which can hold water and gets sunlight with proper temperature hence the grass grows in a place which has all abiotic factors responsible for its growth but in desert these abiotic factors are not available for the growth of grass.

Question.  What is biological magnification? Explain giving one example.
The accumulation of chemicals in the top most organism of the trophic level or food chain is called biological magnification.
Example: Farmer sprays pesticides on the crops which enters the food chain, from crops these pesticides enter into the organisms that feed on it.
grass ⎯⎯→ grasshopper ⎯⎯→ frog ⎯⎯→ snake ⎯⎯→ hawk
In this food chain the maximum amount of pesticide will be found in the top most organism i.e., in hawk the chemical keeps accumulating.

Question.  What is the importance of ozone in the environment why is it depleting? What precautions are taken to preserve it?
Ozone is present in the stratosphere. It protects the earth from harmful ultraviolet radiations. UV ray causes various diseases to organisms e.g. skin cancer, cataract in human beings.
Ozone layer is depleting because of chlorides and fluorides. They act on ozone molecules and deplete it. Chlorides, fluorides are present in CFC’s which are used in refrigerants and fire extinguishers.
CFC ⎯⎯→ Chlorofluorocarbon
The precautions taken to preserve the ozone layer is to ban the use of CFC’s.

Question.  “Damage to the ozone layer is a cause of concern”. Justify this statement suggest any two steps to limit this damage.
Ozone is a molecule of oxygen with 3 atoms i.e., O3. It is formed due to sunlight at higher levels with higher wavelength.

CBSE Class 10 Science Our Environment Assignment Set A-

Ozone is found in stratosphere shielding the earth by protecting it and by not allowing UV rays to reach the earth.
If these rays will reach the earth then many harmful diseases are caused like skin cancer, cataract, it also affects the growth of plants and vegetation.
Two steps to limit the damage of this layer are:
(i) Do not use aerosols, or any products which will release CFC (chlorofluorocarbon)
in the atmosphere.
(ii) Ban on use of CFC as refrigerant and in fire extinguishers.

Question. What is meant by tropic level in a food chain? Construct a terrestrial food chain with four trophic levels. The energy flow in a food chain is always unidirectional. Why?
Answer:  Trophic level = Each step or level of the food chain forms a trophic level. Terrestrial food chain Grass → Grasshopper  Frog → Snake Producer Herbivore Primary Secondary (Autotrophs) (Primary consumer) carnivore carnivore Flow of energy in an ecosystem is unidirectional Each organism needs energy to carry on vital activities and for building up and repairing the body tissues.
(1) The ultimate source of energy used by living organisms is the sun.
(2) Only 1% of solar radiations are captured by green plants in a terrestrial ecosystem and converted into food energy by photo synthesis. This energy is stored as chemical energy of food.
(3) When green plants (producers) are eaten by primary consumers (Herbivores) a lot of heat is lost as heat to the environment and other activities. Only 10% of the food eaten is turned into its new body and is available for the next level of consumers (Primary carnivores).
(4) Only 10% amount of organic matter reaches the next level of consumers (secondary carnivores).
(5) Since, amount of available energy goes on decreasing at each trophic level, food chains usually consists of only 3 to 4 trophic levels. For example grass receives 6000 j of energy from the sun. It will pass 10% of energy as per 10% law to grasshopper i.e. 600 j and so on.

Question. (A) Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why?
(B) What are decomposers? What will be the consequence if the decomposers are completely eradicated from an ecosystem? Give justification in support of your answer. 
Answer:  (A) Natural water bodies are natural ecosystems in which the diversity of organisms is balanced and the wastes produced are naturally eliminated from water as they are decomposed by the decomposers present. Whereas an aquarium is a man made ecosystem in which selective organisms have been kept and maintained in a restricted and artificial environment. As there are no decomposers, the uneaten food and wastes produced by the fishes keeps accumulating and hence requires regular cleaning.
(B) The decomposers are the various organisms in the ecosystem which help in decomposing the dead bodies of plants and animals by breaking down the complex organic substances into simpler inorganic substances. If decomposers are completely eradicated from our ecosystem:
(1) The ecological balance would be disturbed.
(2) Wastes of organisms and dead plants and animals would pile up leading to foul gases, diseases and deaths.
(3) The soil would lose its fertility as there will be no recycling of nutrients.
(4) The bio geo chemical cycles which are natural ways of nutrient cycling would be affected leading to insuffcientnutrients.

Question. Suggest suitable mechanism(s) for waste management in fertiliser industries. 
Answer:  Effluents and harmful gases are the main wastes, which are produced in a fertiliser factory. Suitable mechanism for waste management are:
i. For the control of gaseous pollutants combustion equipments are used which can be oxidised. The pollutants are exposed to a high temperature in the process. Air pollutants, such as certain gases and vapour and inflammable compounds are controlled through the use of adsorption equipments. Adsorption is a surface phenomenon that needs the presence of a large solid surface area. Toxic and odoriferous compounds are efficiently removed by this process.
ii. Three options available for controlling the effluents are:
a. Control can take place at the point of generation within the factory.
b. Waste water can be pre-treated for discharge to municipal treatment systems.
c. Waste water can be treated completely in a factory and either reused or discharged directly for receiving water.

Question. Give reason to justify the following:
(a) The existence of decomposers is essential in a biosphere.
(b) Flow of energy in a food chain is unidirectional.
(a) Decomposers break down complex organic substances (dead remains and waste products of organisms) into simpler inorganic substances that can be absorbed by the plants.
They are essential for the proper functioning of an ecosystem.
• Decomposers play an important role in the cycling of materials in the biosphere.
• By decomposing dead bodies of plants and animals they help in cleaning the environment.
• They replenish the soil naturally.
(b) In the ecosystem energy flows from one trophic level to the next trophic level of the food chain. Energy flows from producers, i.e., green plants to the consumers. It does not flow from the last consumers to its previous consumers and so on. The energy captured by the autotrophs does not go back to the solar input. Thus the energy does not flow back from consumers to the producers. Hence the flow of energy in a food chain is unidirectional

Question. List three problems which arise due to construction of big dams. Suggest a solution for these problems.
Answer. Three problems that arise due to construction of big dams:
1. Social problems. Due to the construction of high rise dams, a large number of human settlements are submerged in the water of large reservoir formed by the dam and many people are rendered homeless.
2. Environmental problems. The construction of high-rise dams leads to deforestation and loss of biodiversity as vast variety of flora and fauna get submerged in the water of large reservoir formed by the dam and disturbs the ecological balance.
3. Economic problems. Some people believe that the construction of high-rise dams involves the spending of huge amounts of public money without the generation of proportionate benefits.
Suggestions for these problems. All the people who are displaced from the dam site should be given adequate compensation by the Government for rehabilitation so as to start their life afresh.

Question. The activities of man had adverse effects on all forms of living organisms in the biosphere. Unlimited exploitation of nature by man disturbed the delicate ecological balance between the living and non¬living components of the biosphere. The unfavourable conditions created by man himself threatened the survival not only of himself but also the entire living organisms on the mother earth. One of your classmates is an active member of
‘Eco-club’ of your school which is creating environmental awareness amongst the school students, spreading the same in the society and also working hard for preventing environmental degradation of the surroundings.
(a) Why is it necessary to conserve our environment?
(b) State the importance of green and blue dust-bins in the safe disposal of the household waste.
(a) It is necessary to conserve our environment because of the following reasons:
• To save natural resources like air, water and soil from pollution which are essential for our survival.
• To maintain ecological balance in nature.
• The environment provides us fresh air to breathe, a number of useful products such as wood, paper, medicines, etc. The ozone layer of the environment also protects us from harmful ultraviolet radiations from the sun.
(b) Green dustbins are used for biodegradable wastes and blue dustbins are used for nonbiodegradable wastes.
Importance of two types of dustbins
• Disposal of wastes after separating them into biodegradable and non-biodegradable wastes in separate dustbins and treating wastes properly before dumping in landfills.
• Segregation of biodegradable and non-biodegradable wastes occur without wasting time and energy.

Question. After the examinations, Rakesh with his friends went on a picnic to a nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc. and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials & respectively dispose them off separately in the green and red dustbins placed in the comer of the park. In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the advantage of the method suggested by Rakesh.
Burning of plastic is not an eco-friendly method of waste disposal because it produces toxic gases which cause too much air pollution. It has an adverse effect on the health of all types of living organisms including human beings. The method of waste disposal used by Rakesh is advantageous as the leftover food and peels of fmits are biodegradable and can be used as manure. The plastic bags and cans should be disposed off in red dustbins from where they can be sent for recycling, thereby keeping the environment clean.

Question. A team of Indian researchers went to Antarctica to study the ozone layer. They confirmed the presence of largest ozone hole over Antarctica and it was just short of 27 million sq. km. After a few days of their return, one of the scientists developed rashes, burning sensation and other skin problems which the doctors have confirmed as skin cancer.
(a) What may be the cause of cancer just after return from Antarctica?
(b) What do we learn from this incident?
a) The scientists were exposed to harmful UV-radiations of the sunlight as there was a big hole over Antarctica and this might be the cause of skin cancer. The ozone layer acts as an ozone shield and absorbs the harmful UV-radiations. The UV-radiations have extremely harmful effects on human beings, animals as well as plants.
(b) We learn that the ozone layer is very important for the existence and survival of life on earth. Ozone layer absorbs high energy UV-radiations causing a rise in temperature of the stratosphere. The use of chemicals like CFCs has endangered the ozone layer. CFCs used as refrigerator coolants rise to the stratosphere where these molecules are broken down by UVrays resulting in attack on the ozone molecules damaging the ozone umbrella of earth.
Due to ozone layer depletion UV-rays reaching the earth cause skin cancer, cataracts, damage immune system, etc. UV-rays also decreases crop yield and certain fish larvae which are important constituents of aquatic food chains. It may also disturb global rainfall causing ecological disturbance. In this way all on the earth would be destroyed gradually.

Question. State in brief two ways in which non-biodegradable substances would affect the environment. List two methods of safe disposal of the non-biodegradable waste.
Answer. Non-biodegradable wastes cannot be decomposed into simpler harmless substances by the action of micro-organisms. These substances persist in the environment and cause adverse effects on the environment.
1. The use of pesticides, insecticides has increased agricultural output but the chemicals present in them enter water and food chains. This affects the fertility of the soil and causes water and soil pollution.
2. Plastic bags have changed the modem lifestyle but cause severe problems. They cause blockages in the drainage systems and these plastic bags when eaten by stray animals cause harm to them.
Methods of safe disposal of the non-biodegradable waste. (i) Molten plastic waste mixed with asphalt can be used for making roads, (ii) Solid wastes should be buried in the urban areas as land fills.

Question. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose nonbiodegradable waste, for saving the environment.
Difference between biodegradable substances and non-biodegradable substances.
Biodegradable waste:
1. Wastes which can be broken down into non-poisonous substances in nature in due course of time by the action of micro-organisms are called bio-degradable wastes.
2. Plastic, glass, etc.
Non-biodegradable waste:
• Wastes which cannot be broken down into non-poisonous substances in nature are called non-biodegradable wastes.
• Sewage, peals of fruits and vegetables, etc.
Habits for disposing non-biodegradable waste:
• Disposal of wastes after separating them into biodegradable and non-biodegradable wastes in separate dustbins and treating wastes properly before dumping in landfills.
• Encourage the use of gunny bags, jute bags and paper bags in place of polythene/plastic bags.
• Recycle the plastic and glass objects after use.

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.

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