CBSE Class 10 Biology Our Environment Worksheet Set C

Question. What is the position of human beings in any food chain?
Answer : Human beings occupy the top position in any food chain.

Question. Give a scientific term for each of the following:
(a) The component which includes physical environment, nutrients and climatic factors
(b) The physical and biological world where the organisms live
(c) Organisms which eat both plants and flesh of other animals
(d) A position in a food chain
(e) Accumulation of chemicals at successive trophic levels of a food chain
(f) Organisms which obtain food from other living organisms
Answer : (a) Abiotic component
(b) Ecosystem
(c) Omnivores
(d) Trophic level
(e) Biomagnification
(f) Carnivores

Question. Why do only autotrophs capture the energy present in the sunlight?
Answer : Because autotrophs have chlorophyll that absorb solar energy

Question. Do microorganisms like bacteria play any role in an ecosystem?
Answer : Microorganisms act as decomposers in an ecosystem.

Question. Why is straight line food chain not common in the natural ecosystem?
Answer : Because many animals eat more than one kind of food

Question. What is UNEP agreement of 1987?
Answer : To freeze the production of chlorofluorocarbon at the 1986 level

Question. Fertilizers and pesticides are used in the soil. How do they reach the food grains and vegetables?
Answer : Plants absorb chemicals along with nutrients from soil.

Question. What is the function of ozone in the upper atmosphere? 
Answer : Ozone layer protects the earth from harmful radiations like high energy ultraviolet radiations.

Question. State the essential function performed by Ozone at the higher levels of the atmosphere.
Answer : It shields the surface of the earth from ultraviolet (UV) radiation from the sun. 

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

Question. List two biotic components of an ecosystem.
Answer : Plants, animals, micro-organisms.

Question. Write one negative effect, on the environment, of affluent life style of few persons of a society.
Answer : Use of excessive non-biodegradable material in packaging:
Excessive use of natural resources like coal and petroleum which causes pollution.
Affluent lifestyle results in generation of excessive waste materials.

Question. List two natural ecosystems.
Answer : Natural ecosystem—Forest/Lake/Pond/River.

Question. Why is a lake considered to be a natural ecosystem?
Answer : Because a lake is a self-sustaining system. 

Question. What is biodegradable substance?
Answer : Substances that can be broken down by microorganisms in natural simple harmless substances.

Question. Give reason why a food chain cannot have more than four trophic levels. 
Answer : The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

Question. We often use the word environment. What does it mean? 
Answer :Environment is everything that surrounds us. It is the physical, chemical and biological conditions of the region. 

Question. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer. 
Answer : Chlorofluorocarbons. 

Question. The first trophic level in a food chain is always a green plant. Why?
Answer : Green plants are producers. The first trophic level in a food chain is producer i.e., those organisms which produce food by photosynthesis. 

Question. Why is forest considered as a natural ecosystem ?
Answer : A forest ecosystem is a natural woodland unit consisting of all plants, animals and micro-organisms,in an area functioning together with all of the nonliving physical factors of the environment. 

Question. Explain how ozone being a deadly poison can still perform an essential function for our environment. 
Answer : Ozone layer protects us from harmful effects of UV radiation. 

Question. Why should biodegradable and non-biodegradable wastes be discarded in two different dustbins?
Answer : Separation should be done actually to save our resources for future benefits and to save our environment from pollution.

Question. What is ecosystem?
Answer : Ecosystem is the functional unit of the environment comprising of the living and nonliving components. 

Question. In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes?
Plants → Rats → Snakes → Hawks
Answer : Snakes = 500 x 10/100 = 50 J
               Hawks = 50 x 10/100 = 5 J
(According to 10 percent Law)

Question. The following organisms form a food chain.
Which of these will have the highest concentration of non- biodegradable chemicals?
Name the phenomenon associated with it: Insects, Hawk, Grass, Snake, Frog.
Answer : Hawk.
Biomagnification. 

Question. The depletion of ozone layer is a cause of concern. Why?
Answer : Ozone layer shields the earth surface from ultraviolet (UV) radiation of the Sun. These UV-rays may reach the earth due to depletion of ozone layer and cause health hazards/skin cancer in human beings. Therefore, it is a cause of concern.

Question. List two man-made ecosystems.
Answer : Garden and Aquarium. 

Question. Why do producers always occupy the first trophic level on every food chain?
Answer : Because producers (plants) have the ability to trap solar energy with the help of chlorophyll.

Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? 
                             Plants → Deer → Lion
Answer : Plants are producers. So, energy available to the producer is 10,000 J. 

Question. Why is excessive use of CFCs a cause of concern? 
Answer : When CFC’s reach upper layers of the atmosphere, they cause depletion of ozone layer, and allow harmful UV radiations to reach the surface of the earth to create health hazards. 

Short Answer Type Questions :

Question. Give any two ways in which biodegradable substances would affect the environment.
Answer : (i) They produce foul smell during decomposition process. 
(ii) They may produce harmful gases such as ammonia, methane and carbon dioxide. 

Question. Differentiate between natural and artificial ecosystem.
Answer : Natural ecosystem
Naturally occurring ecosystem
E.g., pond, grassland, forest
Artificial ecosystem
These are man-made ecosystem
E.g., garden, aquarium, crop-field.

Question. Why are bacteria and fungi called decomposers?
List any two advantages of decomposers to the environment? 
Answer : Bacteria and fungi are called decomposers because they decompose or consume the dead remains of other organisms.
Advantages :
(i) Decomposers degrade garbage and the organic wastes which would otherwise cause environment problems.
(ii) Decomposers recycle the nutrients through biochemical cycle. 

Question. With the help of an example of a food chain, prove that the flow of energy in the biosphere in unidirectional. 
Answer :

(1) At each trophic level only 10% of the energy is passed on to the next and the rest is either utilized for its own metabolic activities or is lost in the environment as heat.
(2) Lost energy is not returned to the previous level/Solar input.

Question. Write the harmful effects of using plastic bags, on the environment. Suggest alternatives to plastic bags. 
Answer : Plastic bags are non-biodegradable wastes, they are not degraded, they begin to stink, emitting foul gases, spoil the beauty of places and contaminate soil, water and air with toxins.
Cloth bags are used instead of plastic bags because they are stronger, more durable and washable. 

Question. (a) Define ecosystem.
(b) Autotrophs are at the first level of food chain. Give reason.
(c) In a food chain of frogs, grass, insects and snakes, assign trophic level to frogs. To which category of consumers do they belongs to?
Answer : (a) Ecosystem: It is the functional unit of the environment comprising living and non-living components.
(b) The first trophic level in a food chain is always producers (plants) because they have the ability to trap solar energy with the help of chlorophyll. As a result, they produce food by photosynthesis.
(c) Frogs are secondary consumers. 

Question. (i) Create a terrestrial food chain depicting four trophic levels.
(ii) Why do we not find food chains of more than four trophic levels in nature? 
Answer : (i) Rice (Producers) → Rat (Herbivores) → Snake (Carnivores) → Peacock (Top carnivores)
(ii) This is because according to 10 percent law of energy transfer, only 10 percent of the energy passes from one trophic level to the next. Thus, the amount of energy goes on decreasing with the successive trophic levels. 

Question. Write the essential function performed by ozone at the higher levels of the Earth’s atmosphere?
How is it produced? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced?
Answer : Ozone protects the surface of earth from harmful ultraviolet (UV) radiations emitted by the sun. Ozone is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms. These atoms combine with molecular oxygen to form ozone.
                           O₂ →^UV O + O
                           O + O₂ → O₃
                                        (zone)
Chlorofluorocarbons (CFCs) are mainly responsible for the drop of amount of ozone in the atmosphere. Use of these chemicals can be reduced by using alternate products that do not harm the ozone layer. Also, safe disposal of old appliances like refrigerators prevents its emission.

Question. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.
Answer : An ecosystem can be defined as a functional unit of nature, where living organisms interact among themselves and with the surrounding physical environment.
Diagram to show the flow of energy in an ecosystem: Assuming 10,000 J of energy is available to the producers, then 1000 J will be available to the primary consumers, 100 J will be available to secondary consumers and 10 J will be available to tertiary consumers.

Question. Give reason to justify the following:
The existence of decomposers is essential in a biosphere. 
Answer : The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants.
Thus, decomposer:
(a) replenish the soil naturally,
(b) helps in removing the biodegradable waste. 

Question. How is ozone both beneficial and damaging? How can we prevent the damaging effect of ozone?
Answer : Damaging as it is a deadly poison. Beneficial as it shields the surface of the earth from UV radiations of the Sun.
By not using synthetic chemicals like CFCs, that deplete layer. 

Question. (a) Explain the role of UV radiation in producing ozone layer.
(b) Mention the reaction involved.
(c) Why is excessive use of CFCs a cause of concern?
Answer : (a) Ozone is formed in the upper atmosphere when solar UV radiation dissociate molecules of oxygen (O) and then this oxygen atom (O) combines with an oxygen molecule.
(b) Reaction involved: O2 →^UV O + O
                                 O + O₂ → O₃
(c) When CFC's reach upper layers of the atmosphere, they cause depletion of ozone layer, and allow harmful UV radiations to reach the surface of the earth to create health hazards. 

Question. How will you create an artificial aquatic ecosystem, which is self-sustainable? 
Answer : (a) Large jar filled with water, oxygen, food and aquatic plants and animals.
(b) Oxygen/oxygen pump.
(c) Fish food.
(d) Aquatic plants/Producers provide O₂ during photosynthesis.
(e) Aquatic animals/Consumers release CO₂ for the process of photosynthesis.
(f) Decomposers are also important for natural cleaning of the aquarium. 

Question. Your mother always thought that fruit juices are very healthy for everyone. One day she reads in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health.
(a) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit may cause harm and damage our organs. Name the phenomenon and write about it.
Answer : (a) (i) Farmers generally use pesticides on fruit crops to protect their crops from plant diseases. However, pesticides may contaminate the fruit and therefore fruit juices also become contaminated. 
(ii) Using contaminated ground water for irrigation also makes the fruits infected with contaminants. 
(b) Biological magnification or biomagnification is the accumulation of chemicals in the individuals of higher trophic level. Chemicals are nonbiodegradable and their concentration increases at each trophic level. Humans, being at the top of food chain, also receive higher concentration of these harmful chemicals resulting into various health
problems. 

Question. How is ozone layer formed? State its importance to all life forms on earth? Why the amount of ozone in the atmosphere dropped sharply in the 1980s?
Answer : Formation of ozone in Atmosphere: Ozone is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere. The high energy ultraviolet radiations split ozone into molecular and atomic oxygen with large amount of heat. This heat is used in warming the stratosphere.
                                              O₃ → O₂ + [O] + Heat
This oxygen atom then recombine with oxygen (O₂) molecule to form ozone molecule.
                 O₂ + [O] → O₃
The ozone layer acts as a protective blanket around the earth which shields the entire earth from harmful ultraviolet radiations that come from the sun. Ozone depletion is the reduction in concentration of ozone layer. It is formed due to an increased concentration of ozone-depleting substances such as chlorofluorocarbons (CFCs). CFCs are used in refrigerants, ACs, fire extinguishers, aerosols spray etc. 

Question. Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies? What is this phenomenon called?
Answer : Food chain is the series formed of organisms feeding on one another at various biotic levels.
Terrestrial Food Chain:
PRODUCERS  → PRIMARY CONSUMERS 
  (Plants)            (Rabbit )
                            →        SECONDARY CONSUMERS
                                                   (Fox)
                                                      ↓
                                      TERTIARY CONSUMERS
                                                   (Lion)
The organisms at the highest (top) trophic level have the maximum concentration of the pollutant in their bodies. This phenomenon is known as biological magnification. 

Question. The flow of energy between various components of the environment has been extensively studied.
Give an outline of the findings.
Answer : (i) Flow of energy is unidirectional.
(ii) Terrestrial plants take about 1% of the Sun’s energy and change it to chemical energy.
(iii) A great amount of energy is lost as heat/ used for digestion/doing work/growth and reproduction.
(iv) Only 10% of organic matter present at each trophic level (and available to the next trophic level).
(v) Food chains are mainly of 3-4 trophic levels (because of 10 percent law).
(vi) The number of producers are maximum (the number reduces in subsequent trophic levels).
(vii) Food webs are more common (as compared to isolated food chains).
(viii) Biological magnification can be observed.

Question. 'Energy flow in food chains is always unidirectional'. Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Answer : (i) In a food chain the energy moves progressively through the various trophic levels and is no longer available to the organisms of the previous trophic level/ energy captured by the autotrophs does not revert back to the solar input. 
(ii) Pesticides used for crop protection when washed away/down into the soil/water bodies absorbed by plants/ producers. 
(iii) On consumption they enter our food chain and being non-biodegradable, these chemicals get accumulated progressively and enter our body. 

Question. State two advantages of conserving (i) forests and (ii) wildlife. 
Answer : Two advantages of conserving forests are:
(i) Forests maintain balance between abiotic and biotic factors of the environment.
(ii) They provide us various products in the form of food, medicines, wood and raw materials for different industries. 
Advantages of conserving wildlife are :
(i) For protecting biodiversity.
(ii) Some wildlife of animals are essential for the survival of other animals. 

Question. You have been selected to talk on 'ozone layer and its protection' in the school assembly on ‘Environment Day‘.
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Answer : (i) Ozone layer helps in shielding the Earth from the harmful UV radiations coming from sun. If ozone layer gets depleted, UV radiations can directly reach the earth's surface and drastically affect the life on earth.
(ii) Ozone layer can be protected by:
(a) Stopping the release of Chlorofluorocarbon
(b) Removing the pollutant nitrogen monoxide
(c) Reduce the usage of air conditioners.

Question. What is Ozone? Name the chemicals that damage the Ozone layer. 
Answer : Ozone is a gas made up of three oxygen atoms, occurs naturally in small amounts in the upper atmosphere and protects life on Earth from the Sun's ultraviolet (UV) radiations. The chemical that damage Ozone layer is Chlorofluorocarbon (CFCs).

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose off the waste produced in our homes.
Answer : (a) Harmful effects of plastic bags:
(i) Plastics do not undergo degradation, thus stay in soil for many years. This may affect the soil fertility and degrades the soil quality.
(ii) When plastic artifacts enter the drainage and sewerage system, they block the pipes and drains causing water logging.
(iii) Littering of plastics in open spaces creates unhygienic conditions, as it acts as breeding ground for insects and mosquitoes. 
We can reduce the use of plastic bags and carry jute bags and paper bags to carry items from the market.
(b) Measures taken for proper disposal of waste produced at our homes are:
(i) Prepare a compost pit for kitchen wastes.
(ii) Safe disposal of plastic bags.
(iii) Segregation of biodegradable and non biodegradable wastes.
(iv) Fruit peels can be placed near trees or plants, which on decomposition will enrich the soil with nutrients.
(v) Recycling of paper wastes. 

Question. Plastic cups were used to serve tea in trains in early days- these could be returned to the vendors, cleaned and reused. Later, Kulhads were used instead of plastic cups. Now, paper cups are used for serving tea.
What are the reasons for the shift from Plastic to Kulhads and then finally to paper cups?
Answer : Plastic cups are non-biodegradable and harm the environment. They were, thus, replaced by Kulhads.
Making Kulhad, which is made of clay on a large scale resulted in the loss of top fertile soil. Now, disposable paper cups are used because the paper can be recycled, it is biodegradable and is eco-friendly material, which does not cause environmental pollution. 

Question. Draw a labelled diagram to illustrate energy flow in an ecosystem. 
Answer : 

Energy flow is unidirectional, dissipated at each level. Matter flow is cyclic and no loss of matter.

Question. Students in a school listened to the news read in the morning assembly that the mountain of garbage in Delhi, suddenly exploded and various vehicles got buried under it. Several people were also injured and there was traffic jam all around. In the brain storming session, the teacher also discussed this issue and asked the students to find out a solution to the problem of garbage. Finally they arrived at two main points – one is self management of the garbage we produce and the second is to generate less garbage at individual level.
(a) Suggest two measures to manage the garbage we produce.
(b) As an individual, what can we do to generate the least garbage? Give two points.
(c) List two values the teacher instilled in his students in this episode. 
Answer : (a) Incineration/Waste compaction/Biogas generation/Composting/Segregation and safe disposal/ Vermicomposting 
(b) Reuse of empty bottles, books etc.
Reduce the use of non-biodegradable substances like polythene, thermocol, etc. 
(c) Awareness about environment, scientific attitude, concern for community health and personal health.

Question. (a) From the following groups of organisms create a food chain which is the most advantageous for Human being in terms of energy.
(b) State the possible disadvantage if the cereal plant is growing in soil rich in pesticides.
(c) Construct a food web using the organisms mentioned above.
Answer : (a) Short food chains are more efficient in terms of energy. The shorter the food chain is, more is the available amount of energy.
            Cereal Plant → Human being
(b) Harmful for human consumption as the traces of pesticide will be carried by food.
(c) 

Question. How can you help in reducing the problem of waste disposal? Write any two methods.
Answer : We can help in reducing the problem of waste disposal by these methods:
(i) By separating biodegradable substances from nonbiodegradable substances.
(ii) By reducing, reusing and recycling nonbiodegradable substances. 

Question. (a) State with reason the consequence of decrease in number of carnivores in an ecosystem.
(b) In a food chain, state the trophic level at which the concentration of harmful chemicals is maximum.
Why is it so? 
Answer : (a) The carnivores keep the populations of other carnivores and herbivores help to keep check. If there were no carnivores, the herbivore populations would rise exponentially and they will rapidly consume large amounts of plants and fungi, growing until there is not enough food to sustain them. Eventually, the herbivores would starve, leaving only those plants that were distasteful or poisonous to them. Species diversity would, therefore, drop dramatically.
(b) The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification. The level of biomagnification would increase as the trophic level increases and would be highest for topmost trophic level. It is because certain harmful substances, usually ones not found in nature but introduced by man, may get accumulated into plants and/or animals. These poisonous substances may not be broken down in the body or excreted easily. Instead, they accumulate in the tissues, and as the living organism eats more, the concentration of these substances increases and pass from one trophic level to the next. The maximum concentration is accumulated at the top carnivore’s level.

Question. Differentiate between the food habits of organisms belonging to first and second trophic levels.
Answer : Difference between food habits of organisms belonging to first trophic level and second trophic level:
(a) The organisms at the first trophic levels are primary producers which make organic compounds using inorganic inputs like light, water, carbon dioxide etc. e.g., Plants.
(b) The organisms at the second trophic level are primary consumer. They are herbivores who eat plants (producers) for nutrition. e.g., Deer. 

Question. Differentiate between biodegradable and nonbiodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.
Answer : 

Question. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes, but an aquarium needs to be cleaned regularly. Why is it so? Explain.
Answer : Ecosystem is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non–living constituents of the environment.
Two main components of Ecosystem are:
(i) Biotic component
(ii) Abiotic component
An aquarium is an artificial and incomplete ecosystem compared to pond or lakes which are natural, self–sustaining and complete ecosystem where there is a perfect recycling of materials.
We need to clean the aquarium because of the:
(i) absence of natural decomposer.
(ii) stagnancy 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. 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. Why decomposers are necessary in environment?
Answer : Decomposers act on all biodegradable substances and break them into simple inorganic materials and maintain the balance of materials in the ecosystem and cleanse the environment.

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

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

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

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

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

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

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

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

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

Long Answer Type Questions :

Question. Suggest suitable mechanisms for waste management in fertiliser industries.
Answer :  Effluents and harmful gases are the major pollutants which are generated in a fertiliser, chemical or pesticides factory. Scientific mechanism for reduction in emission of pollutants in environment is :
For reduction of gaseous pollutants, electro-static precipitators (ESP) are commonly used. ESP works on the principle of "opposite charges attract." When the gaseous emissions containing unburnt pollutants such as coal particles, unburnt carbon, SO_x, NO_x, etc. enters this field, ash particles gets charged and attracted towards the collecting plates due to the force produced by the electric field. Thereby, reducing the gaseous emissions in the atmosphere. 
In addition to this, industrial waste water generated from the fertiliser industry contains pollutants that may contaminate our natural water resources. For safe disposal of industrial waste water, effluent treatment plant (ETP) is set up to treat the waste water. An ETP is used to purify water and remove any toxic and non-toxic materials or chemicals from it. They use evaporation and drying methods, and other auxiliary techniques such as centrifuging, filtration, incineration for chemical processing and effluent treatment. The treated water can be used in the industrial process and for irrigation of plantation. 

Question. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 
Answer :  Ozone layer is a protective shield around the Earth. It prevents harmful ultraviolet radiation of the Sun from reaching the Earth. Air pollutants, like chlorofluorocarbons (CFCs), are causing depletion of ozone layer.
Depletion of ozone layer is allowing greater amount of UV radiation to reach the Earth. UV radiation can affect the ecosystem by affecting photosynthesis in plants, destroying planktons and decomposers. In human beings, UV radiation may cause skin cancer, cataract and damage to immune system.
Many developed as well as developing nations of the world have agreed to sign and obey the directions of UNEP (United Nations Environment Programme) to cease the production of CFCs or to limit their production to some extent.

Question. Explain some harmful effects of agricultural practices on the environment.
Answer :  Some harmful effects of agricultural practices on the environment are :
(i) Excess use of ground water for agriculture lowers the water level. 
(ii) Excessive use of fertilisers affects the soil pH and kills useful microbes. 
(iii) Excessive use of chemical pesticides lead to biomagnification.
(iv) Extensive agriculture causes loss of soil fertility. 
(v) Burning of agricultural waste like paddy and wheat straw results into the formation of smog that pollutes environment substantially. 
(v) It affects our natural eco-system. 

Question. Suggest any four activities in daily life which are eco-friendly.
Answer :  Activities in daily life which are eco-friendly are given below :
(i) Use of compost and vermicompost in place of fertilisers.
(ii) Separation of biodegradable and non-biodegradable substances. 
(iii) Gardening 
(iv) Use of gunny bags or paper bags in place of polythene. 
(v) Rain water harvesting. 

Question. Name the wastes which are generated in your house daily. What measures would you take for their disposal? 
Answer :  The wastes which are generated in our house daily are :
(i) Paper wastes like newspapers, bags, kitchen wastes, etc.
(ii) Plastic bags.
(iii) Vegetable or fruit peels. 
Measures taken for proper disposal are:
(i) Prepare a compost pit for kitchen wastes.
(ii) Safe disposal of plastic bags.
(iii) Segregation of biodegradable and non-biodegradable wastes.
(vi) Fruit peels can be placed near trees or plants, which on decomposition will enrich the soil with nutrients. 
(v) Recycling of paper wastes.

Question. (a) Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
(b) What will happen if decomposers are absent in an ecosystem? 
Answer : (a) The flow of energy is generally from Sun → producer → herbivore → carnivore.
Since the flow of energy is progressively from one trophic level to another and does not revert back, it is said to be unidirectional. Further, the available energy decreases in the higher trophic levels making it impossible for energy to flow in the reverse direction.
(b) Decomposers include micro-organisms such as bacteria and fungi that obtain nutrients by breaking down the remains of dead plants and animals.
It breaks down the complex organic substances of garbage, dead animals and plants into simpler inor ganic substances that go into the soil and are used up again by the plants.
In the absence of decomposers, recycling of material in the biosphere will not take place.