CBSE Class 10 Biology Our Environment Management Of Natural Resources Worksheet Set B

Objective Questions

Question : Accumulation of non- biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as:
(a) Eutrophication
(b) Pollution
(c) Biomagnification
(d) Accumulation
Answer :  C

Very Short Answers

Question : Name the radiations absorbed by ozone layer. Give any one cause of the depletion of the ozone layer. Name a disease likely to be caused due to depletion. 
Answer : Ozone layer absorbs the harmful ultraviolet radiations from sun.
One cause of the depletion of the ozone layer is the use of Chlorofluorocarbons (CFCs) in various objects such as refrigerators. Ozone layer depletion may lead to skin cancer in human beings.

Question : Write the mode of nutrition in fungi.
Answer :  Saprophytic mode.

Question : What is the physical environment of an ecosystem called? Give one example.
Answer :  Physical environment of an ecosystem is called the abiotic or non-living component of an ecosystem. This includes factors like air, water. Temperature etc.

Question : What is ozone? Name the chemicals that damage the ozone layer. 
Answer :  Ozone is a molecule formed by three atoms of oxygen.
Synthetic chemicals such as chlorofluoro- carbons (CFC) and aerosols are the chemicals that damage the ozone layer in the atmosphere.

Question : Explain the flow of energy between various components of the environment.
Answer :  (i) Green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves.
(ii) The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
(iii) In a food chain, the greatest number of individuals are at lower trophic level of an ecosystem, the greatest number is of the producers.

Question. Why are green plants called producers?
Answer : Green plants are called producers because green plants synthesize their own food during photosynthesis by taking raw materials from the earth and energy from the Sun.

Question. What is the important function of presence of ozone in earth’s atmosphere?
Answer : Ozone layer absorbs the harmful UV radiations of the sunlight, so this layer is very important for the survival and existence of life on earth

Question. What is the significance of ozone layer?
Answer : The ozone layer is found in the upper regions of the stratosphere where it protects the earth from the harmful ultraviolet rays of the sun. These radiations can cause skin cancer in humans.

Question. What does a trophic level represent in a food chain? State the position of autotrophs and herbivores in a food chain.
Answer : The position of organisms in a food chain or an ecological pyramid is called as a trophic level. Autotrophs are in first trophic level and herbivores are in second trophic level

Question. State one harmful effect of depletion of ozone layer on the living organisms of the ecosystem.
Answer : If the ozone layer in the atmosphere depletes then the extremely harmful ultraviolet radiations coming from the Sun would reach the earth. These uv-radiations would cause skin cancer and other ailments in men, animals and plants.

Question. In a food chain of frog, grass, insect and snake, assign trophic level of frog.
Answer : Food chain. Grass → insect → frog → snake
∴ Frog belongs to 3rd trophic level.

Question. What is an ecosystem?
Answer : Ecosystem is a unit of biosphere where interaction between biotic community and abiotic factors of an area or place takes place with each other

Question. Which of the following are always at the second trophic level of food chains? Carnivores, Autotrophs, Herbivores
Answer : Herbivores are always at the second trophic level of food chains.

Question. Depletion of ozone in the ozone layer is a cause for our worry. Why?
Answer : Depletion of ozone in the ozone layer is a cause for our worry because if the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiation coming from the Sun would reach the earth. These ultraviolet radiations would cause skin cancer and other ailments in men and animals, and also damage the plants.

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 : 10,00,000 Joules.

Question. In the following food chain, 20,000 J of energy was available to the plants. How much energy will be available to man in this chain?
Plants → Sheep → Man
Answer : Plants have 20,000 J of energy available to them. Sheep will get 10% of 20000 J
20000 × 10/100 = 2000 J
Humans will get 10% of 2000 J.
2000 × 10/100 = 200 J

Question. Why are green plants called producers?
Answer : Green plants prepare their own food by photosynthesis with the help of CO₂, H₂O, sunlight and chlorophyll.

Question. Give one protective function of forests.
Answer : Forests help to reduce air pollution

Question. What is the functional unit of environment?
Answer : Ecosystem is the functional unit of environment.

Question. Which of the following are always at second trophic level of food chains?
Carnivores, Autotrophs, Herbivores.
Answer : Herbivores will always be at second trophic level.

Question. The following organisms form a food chain. Which of these will have the highest concentration of nonbiodegradable chemicals? Name the phenomenon. 
Insects, Hawk, Grass, Snake, Frog.
Answer : Hawk is a decomposer and have maximum concentration of non-biodegradable chemicals.
The phenomenon is called Biomagnification.

Short Answers

Question : What will happen if we kill all the organisms in one trophic level?
Answer : If all the organisms in one trophic level are killed then all the organisms of next trophic level which are dependent on these are killed. Next trophic levels will not get food to eat and the entire food chain gets disturbed. At the same time the organisms at the lower trophic level will reproduce and the population will increase in abundance there by disturbing the ecosystem.

Question : What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer : The pesticides and chemicals are absorbed by plants from the soil and enter the food chain. Being non-biodegradable they accumulate progressively at each trophic level.
As human occupy the top level of any food chain, the maximum concentration of chemicals is found in our bodies. This is called biological magnification.
The level of magnification will be different at different trophic levels, the maximum concentrations will be at the highest trophic level and the chemical will be less at lower trophic levels.

Question : If all the waste we generate is bio-degradable, will this have no impact on the environment?
Answer : If all the waste we generate is bio-degradable and is managed in such a way that it
is allowed to decompose then it will have no impact on the environment.

Question :  mention three harmful effects of using polythene bags on the environment. Suggest an effective alternative to these bags.
Answer :  Harmful effects of using polythene bags on the environment are listed below:
(1) Plastic causes land pollution and water pollution as it is a non-biodegradable substance.
(2) Burning of plastic releases toxic gases and causes air pollution.
(3) Plastic bags cause harm to the life of animals when they consume it along with food.
(4) Plastic bags can cause blocking in sewage line.
(5) The surfaces of tiny fragments of plastic may carry disease-causing organisms and act as a vector for diseases in the environment.

Question : List four problems caused by non-biode gradable wastes. 
Answer :  Lot of Problems are caused by non- biodegrad- able wastes. Four Problems are as follow:
(1) Soil Pollution
(2) Water Pollution
(3) Ecological imbalance
(4) Biomagnification

Question : What are the by-products of fertilizer industries? How do they affect the environment?
Answer :  The harmful by-products are gases such as SO₂ and NO. They cause extensive air pollution and are responsible for acid rain. The harmful by-products of the fertilizer industries are:
(1) Gases  SO₂, NO, CO, CO₂, and H₂S.
(2) Solids - Pyrite ashes, calcium carbonate, sand and plastic bag. Effect on environment: The majority of the gaseous by-products like carbon dioxide, and methane are green house gases which contribute to global warming. The rest of the gases like sulphur dioxide and nitrous oxide are air pollutants and lead to acid rain. These gaseous by-products cause breathing and respiratory problems. The solid waste and waste water discharges into the water body. When these wastes are discharged into the water body, they increase the nutrient content of the water and cause algal bloom (increase in the number of algae). Due to algal bloom, algae form a layer on the surface of the water and hence, the oxygen does not reach the water body. Thus affecting the aquatic life. Also, these wastes are non-biodegradable, so they get accumulated at each trophic level by entering the food chain at the producer level and in the process of the transfer of food through food chains, these harmful chemicals such as pesticides , industrial effluents, heavy metals and radioactive substances get concentrated at each trophic level. This is called bio- magnification.

Question : List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer.
Answer :  Two causes of depletion of ozone layer are as follows:
(a) Use of CFCs
(b) Use of Halons
Harmful effects of ozone depletion:
(i) Due to depletion of ozone UV radiation reaches the earth. This UV radiation causes skin cancer, damage to eyes and immune system.
(ii) Ozone depletion may also lead to variation in global rainfall, ecological disturbances and dwindling of global food supplies.

Question. What is meant by “sustainable development” ?
Answer : What is sustainable development? Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

Question. What is silviculture ? What are its advantages ?
Answer : Silviculture is a program started to replenish depleting forests due to deforestation. Advantages: It produces a large quantity of raw materials for timber and paper industries. It increases the area of earth under forests which is helpful in the conservation of wildlife.

Question. Write a short note on ‘Chipko Andolan’ (Hug the Trees Movement).
Answer : Chipko Movement, started in 1970's, was a non violent movement aimed at protection and conservation of trees and forests from being destroyed. The name of the Chipko moment originated from the word 'embrace' as the villagers used to hug the trees and protect them from wood cutters from cutting them. In 1731, the king of Jodhpur in Rajasthan asked one of his ministers to arrange wood for constructing a new palace. The minister and workers went to a forest near a village, inhabited by Bishnois, to cut down trees. A Bishnoi woman Amrita Devi showed exemplary courage by hugging a tree and daring king’s men to cut her first before cutting the tree. The tree mattered much more to her than her own life. Sadly, the king’s men did not heed to her pleas, and cut down the tree along with Amrita Devi. Her three daughters and hundreds of other Bishnois followed her, and thus lost their lives saving trees. The incident inspired the several other rural women, who launched such similar movements in different parts of India. The Chipko Movement gained momentum under Sunderlal Bahuguna, an activist, who spent his whole life persuading and educating the villagers, to protest against the destruction of the forests and the Himalayan mountains by the government. The chipko protests achieved a major victory in 1980 with a 15 years ban on tree felling in the Himalayan forests of the state by the order of Mrs. Indira Gandhi.

Question. Why should we conserve forests and wildlife ?
Answer : It sustains life on the planet, provides clean air and shelter. Also, forests help conserve biodiversity. Forests provide many resources such as food, medicine, fabric, and raw materials.

Question. Describe briefly the ‘khadin’ system of rainwater harvesting practised in Rajasthan.
Answer : A Khadin, also called a Dhora, is an ingenious construction designed to harvest surface runoff water for agriculture. Its main feature is a very long (100-300 m) earthen embankment built across the lower hill slopes lying below gravelly uplands. Sluices and spillways allow excess water to drain off.

Question. What measures would you take to conserve electricity in your house ?
Answer : The following are some steps we can take to save electricity in our homes:
Switch off all unnecessary lights.
Turn off fans when they aren't needed.
Make use of natural light whenever possible.
Make the best use of solar radiation.
Unplug any unused electronics.

Question. Although coal and petroleum are produced by the degradation of biomass, even then we need to conserve them. Why ?
Answer : Coal and petroleum are fossil fuels formed by the degradation of biomass buried deep inside the earth's crust over thousands of years. Hence, if the reservoirs of fossil fuel get depleted they will not be available to us in near future. Thus, we need to conserve them.

Question. Is water conservation necessary ? Give reasons.
Answer : Yes, water conservation is critical. Water is necessary for all living things. Water accounts for approximately 75% of our body weight. We cannot survive without water because it is necessary for all biological processes in our bodies.

Question. Name the products of combustion of fossil fuels like coal and petroleum products. How do they affect us and our environment ?
Answer : Effects of the products of combustion of fossil fuels on humans and the environment: Increased concentration of carbon dioxide causes greenhouse effects. When a high concentration of sulphur dioxide and nitrogen oxide reacts with rain, it causes acid rain. Greenhouse effects can lead to global warming.

Question. Why should fossil fuels like coal and petroleum be used judiciously ?
Answer : Coal and petroleum are fossil fuels that require millions of years to be formed. They are natural resources and are limited in supply. Once exhausted, they cannot be formed again in a short time. Therefore, fossil fuels like coal and petroleum should be used judiciously.

Question. What are the three R’s to save the environment ? Explain with one example of each.
Answer : The three Rs are reduce, recycle and reuse.
The term 'reduce' aims at lowering the usage of natural resources to avoid wastage. For example, using less electricity.
The term 'recycle' aims at using the discarded items by recycling them. For example, recycling paper and plastic and sending them to the respective industries for the formation of new paper and plastic.
The term 'reuse' means using the same thing again and again. For example, using a paper bag over and over again.

Question. What are the main uses of coal and petroleum products ?
Answer : Following are the main uses of coal and petroleum products:
Coal is used in homes and industries as a fuel. It is also used to generate electricity in power plants.
Petroleum products (such as petrol and diesel) are used as fuels in vehicles. Other products (like kerosene and LPG) are used as domestic fuels for cooking.

Question. State any five steps to reduce the consumption of coal and petroleum products.
Answer : Use of solar cookers, solar water heaters, solar panels should be used. Cleaner fuels like LPG and CNG should be used. Use of biofuels such as ethanol or biodiesel should be encouraged. Use of mass transportation (public transport) should be adopted.

Question. Explain why, despite good rains, we are not able to meet the demand for water of all the people in our country.
Answer : Despite good rains, we are not able to meet the demands for water of all the people in our country. This is because our population is increasing at a fast pace. Also, a high yielding variety of crops require more water for irrigation, in urban areas people consume more water and the industrial waste and untreated sewage is discarded into rivers making it contaminated. All these things need a large amount of water; hence, causing water scarcity.

Question. Give one example to show how the participation of local people can lead to the efficient management of forests.
Answer : Chipko Andolan was started by the common people in a remote village named Reni, in Garhwal.
They treated the forest like the sacred groves and they wanted to stop the felling of trees in their locality.
In this movement, when the workers came to cut the trees in the absence of the men of the village and all the women clasped the tree trunks with their arms, in order to save the trees.
Thus movement clearly shows the participation of local people to efficiently manage the forest and maintain the forest.

Question. Explain briefly, how rainwater harvesting is done from open spaces around the buildings in city areas.
Answer : For rainwater harvesting from open spaces around the buildings in city areas, percolation pits are constructed and covered with concrete slabs having holes in it. They are connected to a recharge well via a pipe. The rainwater goes into the percolation pit through the holes of the slab cover. It gets filtered in the pit and enters the recharge well via an outlet pipe and then, slowly, seeps into the soil.

Long Answers

Question : Producers are autotrophs. They manufacture organic food from inorganic raw material. For this they pick up energy from sun and raw materials from the environment. Solar energy is absorbed by chlorophyll and changed into chemical energy. The chemical energy is stored in organic food formed by photosynthesis. Photosynthesis is performed by plants, algae, phytoplankton, blue green algae and some bacteria. Producers are also called transducers or converts as they change solar energy to chemical energy. Food manufactured by producers is used by all organisms including themselves. Producers have also a global impact of keeping the balance of CO₂→ O₂ constant. They absorb CO₂ and release O₂.
(a) Why are photoautotrophs called producers?
(b) Why are environmentalist stressing for growing more trees?
(c) What is the source of energy in the biosphere?
(d) Why are heterotrophs called consumers?
Answer :  (a) Photoautotrophs are chlorophyll containing organisms which manufacture organic food that is made available to all other organisms.
(b) Plantation of more trees will reduce the rising concentration of CO2 being produced because of higher combustion of fossil fuels.
(c) Sunlight
(d) Heterotrophs are organisms which obtain readymade food from outside sources. They are therefore called Consumers.

Question : Good quantity of ozone occurs in upper atmosphere or stratosphere at a height of 11-16 Km over poles reaching 23-25 km above equator. This region is called ozone layer or Ozonosphere. It is highly protective to life on earth as it destroys very harmful short waves ultraviolet radiations of 100-320 nm wavelength. Longer wave ultraviolet radiations (320-390 nm) are allowed to pass through and reach the earth. It was found in 1980s that thickness of ozone layer is decreasing rapidly. On searching for the reason, it was noted that certain man-made chemicals like chlorofluorocarbons and halons are bringing about destruction of ozone. They are called ozone depleting substances (ODS). With great international efforts starting from Montreal Protocol (1987) to Kigali conference (2016), it was decided to eliminate the use of ODS and replace them with safer chemicals.
(a) Where is ozone found in plenty in the atmosphere?
(b) What is the function of stratospheric ozone?
(c) Name an ozone depleting substance?
(d) Name an international effort to check damage to ozone layer.
Answer :  (a) Ozonosphere/Ozone layer in upper atmosphere.
(b) Ozone destroys harmful ultraviolet radiations so that they do not reach the earth.
(c) chlorofluorocarbons
(d) Montreal Protocol (1987) for limiting chlorofluorocarbons production level. 

Question. Why are some substances biodegradable and some non-biodegradable ?
Answer : The micro-organisms like bacteria and other decomposer organisms (called saprophytes) present in our environment are ‘specific’ in their action. They break down the natural substances or products made from natural substances (like dead remains of plants and animals, and their waste products, paper, etc.) but do not break down man-made substances such as plastics, metals and glass objects, etc. So, it is due to the property of decomposer organisms of being specific in their action that some waste substances are biodegradable whereas some are non-biodegradable.

Question. Give any two ways in which biodegradable substances would affect the environment.
Answer : (i) The rotting biodegradable wastes (like rotting plant and animal wastes) act as breeding grounds for flies and cockroaches. These flies and cockroaches carry germs and spread various diseases to people living in that area. (ii) The rotting biodegradable wastes emit foul smell in the environment which makes the life of people in the area miserable.

Question. Give any two ways in which non-biodegradable substances would affect the environment.
Answer : (i) Some of the non-biodegradable wastes (such as pesticides like DDT and metals like mercury) enter the food chain of humans These non-biodegradable wastes get concentrated in human beings and damage their health in the long run. (ii) The excessive use of non-biodegradable fertilisers in agriculture makes the soil either too much acidic or too much alkaline. When the soil becomes too acidic or too alkaline, the crop yield is reduced. (iii) The dumping of non-biodegradable wastes like plastic, glass and metal objects here and there acts as an eyesore and spoils the environment.

Question. What are trophic levels ? Give an example of a food chain and state the different trophic levels in it.
Answer : A food chain represents the flow of food (or energy) in a given set of organisms or living beings. The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In fact, in a food chain, each step representing an organism forms a trophic level. Consider a food chain operating in a grassland which consists of four organisms : Grass → Insects → Frog → Birds In this food chain, grass is the producer and represents the first trophic level. Insects are the herbivores (which eat grass) and represent second trophic level. Frog is the carnivore (which eats insects) and represents third trophic level. And birds are the top carnivores (which eat frogs) and represent fourth trophic level.

Question. What is the role of decomposers in the ecosystem ?
Answer : The decomposers help in decomposing the dead bodies of plants and animals, and hence act as cleansing agents of environment. The decomposers also help in putting back the various elements of which the dead plants and animals are made, back into the soil, air and water for re-use by the producers like crop-plants. This maintains the fertility of soil and the soil would continue to support crops again and again. For example, the decomposers like putrefying bacteria and fungi decompose the dead plants and animal bodies into ammonia (and other simpler substances). This ammonia is converted into nitrates by the nitrifying bacteria present in soil. These nitrates act as fertilizer in the soil and are again absorbed by the plants for their growth.

Question. What is ozone and how does it affect any ecosystem ?
Answer : Ozone is a gas made up of three atoms of oxygen joined together. The molecular formula of ozone is O3. Ozone is formed high up in the atmosphere by the action of ultraviolet radiations (coming from the sun) on the oxygen gas. The ozone layer present high up in the atmosphere protects all forms of life on earth by absorbing harmful ultraviolet radiations coming from the sun. Certain chemicals like chlorofluorocarbons (CFCs) which are widely used in refrigeration, fire extinguishers and aerosol sprayers reach the upper atmosphere and react with ozone gas present in ozone layer and destroy it gradually. Due to this the ozone layer in the upper atmosphere is becoming thinner, allowing more harmful ultraviolet rays to pass through it and reach the earth. Thus, due to the depletion of ozone layer caused by chlorofluorocarbons, more ultraviolet rays reach the earth. These ultraviolet rays can cause skin cancer, cataract in the eyes and damage immune system of human beings. They also harm animals and plants.

Question. How can you help in reducing the problem of waste disposal ? Give any two methods.
Answer : The two methods which can help in reducing the problem of waste disposal are : recycling, and preparation of compost. These are described below. (i) The solid wastes like paper, plastics, glass and metals, etc., are recycled. For example, waste paper is sent to paper mills where it is reprocessed to form new paper once again. The broken plastic articles like plastic bags, buckets, bowls, cups, plates, etc., are sent to plastic processing factories where they are melted and remoulded to make new articles. Similarly, waste metal articles are sent to metal industries where they are melted and recycled as solid metal for various purposes. (ii) Biodegradable domestic wastes such as left-over food, fruit and vegetable peels, and leaves of potted plants, etc., can be converted into compost by burying in a pit dug into ground, and used as manure.

Question. Which of the following groups contain only biodegradable items ?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit peels, cake and lime juice
(d) Cake, wood and grass
Answer : (a), (c) and (d).

Question. Which of the following constitute a food chain ?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer : (b) Grass, goat and human

Question. Which of the following are environment-friendly practices ?
(a) Carrying cloth bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer : (d) All of the above.

Question. What will happen if we kill all the organisms in one trophic level ?
Answer : If we kill all the organisms in one trophic level, then transfer of food (and energy) to the next trophic level will stop due to which the organisms of next trophic level will starve and die or migrate to other areas. The killing of all the organisms in one trophic level will also lead to the overpopulation of organisms in the previous trophic level. These effects will cause an imbalance in the ecosystem. For example, if we kill all the herbivorous animals like deer, rabbits, etc., in a forest, then the carnivorous animals like lions, tigers, etc., will not get food. Due to this, the lions and tigers, etc., will starve and die or migrate from forest and go towards human settlements and attack people. Moreover, in the absence of herbivores like deer, rabbits, etc., the population of the previous trophic level ‘plants’ (or vegetation) will increase too much (because there are no deer or rabbits to eat them). All these effects will create an imbalance in the ecosystem.

Question. Will the impact of removing all the organisms in a trophic level be different for different trophic levels ? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?
Answer : (a) Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels. For example, in the food chain : Grass ⎯⎯→ Deer ⎯⎯→ Lion : (i) If we remove all the lions at the third trophic level, then the number of deer will increase too much. All these deer will eat up all the grass and other plants turning the forest into a desert. (ii) If we remove all the deer at the second trophic level, then lions will not get sufficient food, they will starve and die. Deer eat grass and other green plants, so the amount of grass and other green plants will increase too much. (b) No, all the organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

Question. What is biological magnification ? Will the level of this magnification be different at different levels of the ecosystem ?
Answer : (a) The harmful chemicals like pesticides enter the food chain at the producer level (plant level) and in the process of transfer of food through food chains these harmful chemicals get concentrated at each trophic level. 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. Pesticides are nonbiodegradable chemicals, so they get accumulated at each trophic level. (b) Yes, the level of biological magnification is different for different trophic levels of an ecosystem. For example, in the food chain : Plants → Goat → Man, the harmful chemicals enter into plants from soil and water. When goat eats these plants, the chemicals enter into goat’s body. And ultimately when a non-vegetarian man eats the goat meat, the harmful chemicals are transferred to his body. The level or concentration of the harmful chemicals increases with increasing trophic level. In the above given food chain, the concentration of harmful chemicals is minimum in the plants, higher in the goat and maximum in man.

Question. What are the problems caused by the non-biodegradable wastes that we generate ?
Answer : The non-biodegradable wastes cannot be made less toxic easily, so they cause a lot of problems for us as well as the environment. For example : (i) Some of the non-biodegradable wastes (such as pesticides like DDT and metals like mercury) enter the food chain of humans These non-biodegradable wastes get concentrated in human beings and damage their health in the long run. (ii) The excessive use of non-biodegradable fertilisers in agriculture makes the soil either too much acidic or too much alkaline. When the soil becomes too acidic or too alkaline, the crop yields is reduced.

Question. If all the waste we generate is biodegradable, will this have no impact on the environment ?
Answer : Even if all the waste we generate is biodegradable, it will have an impact on the environment. This is because too much biodegradable waste cannot be broken down into harmless simpler substances by the decomposers like micro-organisms at the right time. Due to this, the biodegradable wastes will go on accumulating in the environment and act as pollutants resulting in harmful effects on the environment. For example, the rotting biodegradable wastes act as breeding grounds for flies and cockroaches, etc., which spread diseases. Moreover, the rotting biodegradable wastes emit foul smell in the environment which makes the life of people miserable.

Question. Why is the damage to the ozone layer a cause for concern ? What steps are being taken to limit this damage ?
Answer : The ozone gas layer high up in the atmosphere is very important for the existence of life on earth because it absorbs most of the harmful ultraviolet radiations coming from the sun and prevents them from reaching the earth. The damage to the ozone layer is a cause for concern because damage to ozone layer will make it thinner which will allow much more harmful ultraviolet radiations (coming from the sun) to reach the earth. These ultraviolet radiations can then cause skin cancer in humans They can also damage the eyes by causing an eye disease called cataract. Ultraviolet rays damage immune system by lowering the body’s resistance to diseases. They also damage crop plants. In fact, if too much damage occurs to the ozone layer and it disappears completely, then all the life on the earth would be destroyed gradually. The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons (CFCs) in refrigeration, fire extinguishers and aerosol sprayers. So, in 1987, in an attempt to protect ozone layer, the United Nations Environment Programme (UNEP) forged an agreement among its member countries to freeze CFC production at 1986 levels. The chlorofluorocarbons (CFCs) are now being replaced by hydroflurorocarbons (HFCs) which do not damage the ozone layer.

Question. (a) What is a natural resource ? Name three important natural resources.
(b) Why do we need to manage our natural resources ?
Answer : (a) Natural resources are the things present in the environment that can be used by humans. Three important natural resources are water, fossil fuels, like coal and petroleum, and forest and wildlife.
(b) We need to manage our natural resources. The reasons for this are given below:
They are limited in amount. We need to manage them so that they can fulfil the need of the present as well that of the coming generations.
This will prevent their exploitation for short term gain.
This will ensure equal distribution of natural resources so that everyone can benefit from their development.
This will also minimise the damage to the environment, which is caused during the extraction and usage of natural resources.

Question. (a) State the advantages of constructing dams across the rivers.
(b) Describe some of the problems associated with the construction of dams.
Answer : (a) Following are the advantages of constructing dams across the rivers:
They can store excess water, thereby preventing floods.
Water from the dams can be used for the irrigation of crops via a network of canals.
After a suitable treatment, people of towns and cities get dam water through pipelines, for usage.
Water falling from the dams is used to generate electricity in hydropower plants.
(b) Following problems are associated with building dams:
Social problems: It makes many people homeless, by submerging large areas of human- settlements, thereby causing a social issue.
Environmental problems: It causes deforestation and loss of biodiversity by submerging large varieties of plants and animals. This creates an ecological imbalance.
Economic problems: This is an issue raised by many people who consider that the construction of dams needs a large amount of public money and there are no proportionate benefits.

Question. (a) Name any five sources of water (other than rivers)
(b) Describe how, the water of river Ganga has been highly polluted.
Answer : (a) Five sources of water are lakes, rains, ponds, wells and glaciers. (b) The water of river Ganga has been highly polluted with industrial discharges and untreated sewage disposal.

Question. (a) Name the major industries which are based on forest produce.
(b) State the main aim of the management of forests and wildlife.
(c) Name the four main stakeholders in the management of forest resources.
Answer : a The various industries which are based on forest produce are; timber industry paper manufacturing industry 'lac' industry and sports equipment industry. b The main aim of the management of forests and wild life is to conserve the biodiversity which we have inherited.

Question. (a) What is meant by rainwater harvesting ? Name some of the ancient structures used for rainwater harvesting by the rural people.
(b) What are the various advantages of water stored in ground ?
Answer : (a) Rainwater harvesting is the method of collecting rainwater so that it can percolate in the soil more efficiently. The ancient structures used for rainwater harvesting by the rural people are Khadin in Rajasthan, Bandharas and Tals in Maharashtra and Ahars in Bihar.
(b) Following are the various advantages of water stored under the ground:
It does not evaporate.
It spreads out to recharge wells and provides moisture to the crops.
It does not promote the breeding of mosquitoes.
It is not contaminated by human and animal wastes.
It can be utilised by the local population.

Questions Based on High Order Thinking Skills (HOTS)

Question. In a village, farmers started cultivating crops all around a lake which was always filled with water. They added lot of materials W to the soil in their fields to increase the yield of crops. Soon they found that the whole surface of water in the lake was covered with a green layer made up of tiny organisms X. After some time, the fish present in the lake started dying in large numbers because they could not get sufficient Y due to a process Z which had occurred in lake water and drained out all the Y present in the water of lake.
(a) What do you think materials W are ?
(b) Name (i) X, and (ii) Y.
(c) What is the process Z known as ?
(d) What happens during the process Z which uses up all the Y present in lake water ?
(e) What does this example tell us about the use of materials like W ?
Answer : (a) Fertilisers (b) (i) Algae (ii) Oxygen (c) Eutrophication (d) When algae die, bacteria use all the oxygen dissolved in water to decompose dead algae (e) Excessive use of fertilisers in fields is not good for the environment

Question. There were lot of organisms A in the crop fields in an area. These organisms used to feed on organisms B also present in the crop fields but which damaged the standing crops. One day some people arrived in the fields and killed all the organisms A so that they could remove their C for making fancy items which were in great demand. Due to large scale killing of A, the population of B increased too much damaging all the crops in the area and causing a famine-like situation. Apart from A, there is another organism D which can also kill and eat B. Name A, B, C and D.
Answer : A : Snakes ; B : Rats ; C : Skin ; D : Cat

Question. There are two important fuels A and B both of which are extracted from deep inside the earth. Fuel A is a thick, dark, foul smelling liquid whereas fuel B is a black solid. Combustion of both the fuels produces products, C, D, E and F. The product C makes the rainwater only slightly acidic but it is mainly responsible for causing global warming. The product D is neither acidic nor basic. It is harmless and does not affect the environment in any way. Both E and F attack breathing system of humans and are mainly responsible for causing acid rain. In addition to combustion of fuels A and B, the product F is also formed when lightning occurs in the sky.
(a) What are (i) fuel A, and (ii) fuel B ?
(b) Name (i) C (ii) D (iii) E, and (iv) F
(c) What is the process of formation of F during lightning known as ?
(d) Which fuel is supposed to be exhausted sooner : A or B ?
(e) Which fuel is mostly used for generating electricity at thermal power plants ?
Answer : (a) (i) Petroleum (ii) Coal (b) (i) Carbon dioxide (ii) Water (iii) Sulphur dioxide (iv) Nitrogen oxides (c) Natural fixation of nitrogen (d) A (Petroleum) (e) B (Coal)

Question. A man bought a device X which could cook pulses, vegetables and rice without using any fuel like wood, coal, kerosene or LPG, etc. This device did not work at night. It also took a lot of time for cooking.
(a) Name the device X.
(b) What is the source of energy which cooks food in this device ?
(c) What is the name of the process which traps energy in this device ?
(d) State one advantage (other than saving on fuel) of using such a device for cooking food.
Answer : (a) Solar cooker (b) Sun (c) Greenhouse effect (d) It does not cause air pollution

Question. A person buys two electrical devices P and Q for lighting purposes in his house. The device P consumes only 5 units of electricity in a month but device Q consumes 15 units of electricity in a month when used for the same number of hours daily. The device Q wastes a lot of electricity by radiating energy C but P does not do so.
(a) What type of device is (i) P, and (ii) Q ?
(b) Name one component which is present in Q but not in P.
(c) Name the energy C.
(d) Which device is more energy efficient : P or Q ?
(e) Which fossil fuel is most likely to be conserved if all of us switch over to devices like P ?
Answer : (a) (i) Compact Fluorescent Lamp (CFL)(ii) Filament type bulb (or lamp) (b) Filament (c) Heat energy (d) P (e) Coal