CBSE Class 10 Science Our Environment Assignment Set A

MCQ Questions for NCERT Class 10 Science Our Environment 

Very Short Answers

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. 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. 

Question. What are various steps in the food chain called?
Answer. Trophic level

Question. In the following food chain, 10 J is energy available to the hawks. How much energy would have been present for the rats? Plants → Rats → Snakes → Hawks
Answer. 1000 J.

Question. Define ecosystem.
             OR
What is an ecosystem?
Answer. All living organisms and abiotic components of surroundings forms an ecosystem.

Question. List two man-made ecosystem.
Answer. Aquarium, crop land, park. (Any two)

Question. During heavy rain in a village the rain water carried excessive fertilizer to a pond. How will it affect the fish production in pond in the long run?
Answer. Fish production will decrease due to formation of excess of algae.

Question. Why are plastics non-biodegradable substances?
Answer. It is because plastics are not decomposed by micro-organisms. (Note: Now, plastic eating enzymes has been discovered).

Question. List two natural ecosystems.
Answer. (i) Oceans, (ii) forests are two natural ecosystems.

Question. “Flow of energy is unidirectional”. Name the first two components of the environment involved in flow of energy from the Sun.
Answer. Producers and primary consumers are first two components in the flow of energy.

Question. Consider a food chain consisting of wheat, rat, snakes, peacock. What will happen if all snakes are killed?
Answer. The peacock will also die. The population of rats will increase.

Question. Draw a food chain which operates in forest ecosystem
Answer. Grass → Deer → Tiger.

Question. Change one consumer each that belongs to the second and third trophic levels from the following organisms : Eagle, frog, tiger, rabbit, fox
Answer. (i) Second trophic level → Rabbit (ii) Third trophic level → Frog and fox.

Question. Crop fields are called artificial ecosystem, Justify.
Answer. Crop field ecosystem is created by man and needs care like watering, supply of manure, protection from diseases. Therefore, it is an artificial ecosystem.

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:
O₂ → 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. 
Answer:

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.

Q19. (a) Distinguish between producers and decomposers.
(b) Classify the following as producers and decomposers.
Green plants, bacteria, fungi, blue-green algae.
Answer:

Question. Why is plastic bag called non-biodegradable while paper is not?
Answer:  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.
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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?
Answer: 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?
Answer: 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?
Answer: 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. 
Answer:

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

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

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

Long Answers

Question.  Enlist various categories of consumers giving examples of each.
Answer: 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.
Answer: 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.
Answer: 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?
Answer: 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.
Answer: Ozone is a molecule of oxygen with 3 atoms i.e., O₃. It is formed due to sunlight at higher levels with higher wavelength.

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

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

Question. What is the importance of ozone in the environment why is it depleting? What precautions are taken to preserve it?
Answer. 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 inhuman 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. Enlist various categories of consumers giving examples of each.
Answer. 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 formation of ozone layer and its importance.
Answer. Ozone is formed when high energy ultra violet radiations split oxygen molecule into oxygen atoms. The oxygen atom combines with oxygen molecules to form a new molecules with three oxygen atoms named ozone.

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

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

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

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

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