OUR ENVIRONMENT

 

OUR ENVIRONMENT

NCERT TEXTBOOK QUESTIONS:

Q.1 Why are some substances biodegradable and some non-biodegradable?

Solution: 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.

Q.2 Give any two ways in which biodegradable substances would affect the environment.

Solution: (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.

Q.3 Give any two ways in which non-biodegradable substances would affect the environment.

Solution: (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 on 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.

Q.4 What are trophic levels? Give an example of a food chain and state the different trophic levels in it. 

Solution: 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 grassland which consists of four organisms:

In this food chain, the grass is the producer and represents the first trophic level. Insects are the herbivores (which eat grass) and represent the 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 the fourth trophic level.

Q.5 What is the role of decomposers in the ecosystem?

Solution: The decomposers help in decomposing the dead bodies of plants and animals and hence act as cleansing agents of the 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 the 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 the soil. These nitrates act as fertilizer in the soil and are again absorbed by the plants for their growth.

Q.6. What is ozone and how does it affect any ecosystem?

Solution: 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 the 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 the ozone layer caused by chlorofluorocarbons, more ultraviolet rays reach the earth. These ultraviolet rays can cause skin cancer, cataract in the eyes and damage the immune system of human beings. They also harm animals and plants.

Q.7 How can you help in reducing the problem of waste disposal? Give any two methods.

Solution: 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 a 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 the ground, and used as manure.

NCERT EXERCISE:

Q.1 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

Solution: (a), (c) and (d).

Q.2 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

Solution: (b) Grass, goat and human

Q.3 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 the school instead of getting your mother to drop you on her scooter

(d) All of the above

Solution: (d) All of the above.

Q.4 What will happen if we kill all the organisms in one trophic level?

Solution: If we kill all the organisms in one trophic level, then the 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 the 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.

Q.5 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?

Solution: (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:

(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.

Q.6 What is biological magnification? Will the level of this magnification be different at different levels of the ecosystem?

Solution: (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 the 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 non-biodegradable 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:  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.

Q.7 What are the problems caused by the non-biodegradable wastes that we generate?

Solution:  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.

Q.8 If all the waste we generate is biodegradable, will this have no impact on the environment?

Solution:  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.

Q.9 Why is the damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Solution:  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 the 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 a cataract. Ultraviolet rays damage the 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 the 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 the 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 hydrofluorocarbons (HFCs) which do not damage the ozone layer.