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NCERT Solutions for class 10 Science chapter 15 – Our Environment

Back Exercise

Question 1.
Which of the following groups contains only easily biodegradable items ?
(A) Grass, flower and leather
(B) Grass, wood and plastic
(C) Fruit peels, cake and lime juice ,
(D) Cake, wood and grass.
Answer:
(A), (C), (D).

Question 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.
Answer:
(B) Grass, goat and human

Question 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 school instead of getting your mother to drop you on her scooter
(D) All the above.
Answer:
(D) All the above

Question 4.
What will happen if you kill all the orgainsms in one trophic level ?
Answer:
The food chain would end and ecological balance would be affected.

1. If the herbivores are killed, then the carnivores would not be able to get food and would die.
2. If carnivores are killed, then the population of herbivores would increase to unsustainable level.
3. If producers are killed, then the nutrient cycle in that area would not be completed.

Question 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 ?

Answer:

1. Yes. Impact of removing all the organisms of a trophic level depends upon the trophic level. Removal of producers will kill all the consumers. Killing of carnivores will increase the number of herbivores which in turn will eat up all the producers. They would themselves die of starvation. However, if herbivores are removed, all the carnivores of the area will die. The plants which are dependent upon animals for pollination will fail to reproduce and die ultimately. Others would persist and increase in number, again much beyond the carrying capacity of the environment.
2. No. Removal of all the organisms of a trophic level will disturb the ecosystem – killing of higher trophic level organisms and explosion in populations of lower level organisms. Higher number of lower trophic level organisms will adversely affect the ecosystem by consuming whole or major part of their prey.

Question 6.
What is biological magnification ? Will the levels of this magnification be different at different levels of the ecosystem ?
Answer:
Definition: The phenomenon that involves progressive accumulation of non-biodegradable chemicals at each trophic level is called bio-magnification or bio-accumulation. In one study it was found that concentration of harmful chemical like DDT will increase 80,000 times the concentration present in water.
Levels of Magnification at Different Levels of Ecosystem. Levels of biomagnification of a chemical will be different at different levels of ecosystem. In one study it was found that concentration of a pesticide was 0.002 ppm in water, 0.05 ppm in plankton, 2.4 ppm in fish and 16.0 ppm in fish eating bird.

Question 7.
What are the problems caused by the nonbiodegradable waste we generate ?
Answer:
Following are the problems caused by the non-biodegradable wastes:

• These substances cannot be decomposed by the microorganisms.
• As the quantity increases, dumping becomes a problem.
• Non-biodegradable wastes like heavy metals may enter the food chain in the upper trophic levels.
• They may escape to the groundwater which causes soil infertility and disturbance in pH of the soil.

Question 8.
If all the waste we generate is biodegradable, will this have no impact on the environment ?
Answer:
The impact on the environment will depend upon the system of collecting, transporting and disposal of biodegradable waste. If it is regular and clean, the impact will be little in urban areas. Only some effect will be observed at disposable site which will emit foul gases and expose the sanitary workers to contamination. The same can also be reduced by increased use of machines and wearing of protective gear by the sanitary workers.

Question 9.
Why is damage to the ozone layer a cause of concern What steps are being taken to limit this damage ?
Answer:
The ozone layer is a protective cover for the earth. It prevents harmful UV rays from entering the earth as these rays harmful and can result in skin cancer. But the air pollutants like chlorofluorocarbons (CFCs) are the main reason for the depletion of the ozone layer. Too much of UV rays are harmful to plants as they affect photosynthesis, destroy planktons and decomposers. These are the reasons why damage of ozone layer is a cause of concern. Steps taken to limit this is that many developing and developed countries have signed and are obeying the directions of UNEP (United Nations Environment Programme) to freeze or limit the production and usage of CFCs.

In-Text Questions

Question 1.
What are trophic levels ? Give an example of a food chain and state the trophic levels in it.
Answer:
Trophic Levels : The various steps in a food chain at which the transfer of food or energy takes place are called trophic levels.
Example : A food chain operating in a grassland is given below :
Grass → Insects → Frog → Birds
In this food chain

1. Grass represents first trophic level.
2. Grasshopper represents second trophic level.
3. Frog represents third trophic level.
4. Eagle represents fourth tropic level.

Question 2.
What is the role of decomposers in the ecosystem ?
Answer:
Following is the role of a decomposer in the ecosystem:

• They act as a cleansing agent of the environment by decomposing the dead plants and animals
• They help in recycling the nutrients
• They provide space for new beings in the biosphere by decomposing the dead
• They help in putting back the various elements into water, soil and air for the reuse of producers like crop plants.

Question 3.
Why are some substances biodegradable and some non-biodegradable ? (CCE 2011)
Answer:
Biodegradable Substances :The substances that are broken down by biological processes, such as the action of bacteria and, other saprophytes into simpler harmless substances in due course of time are called biodegradable substances. For Example - Domestic waste products, agricultural wastes, wood, paper, cloth, etc.
Non-Biodegradable Substances :The substances that are not broken down by biological processes, but are acted upon by physical processes like heat and pressure under the ambient conditions found in the environment are called non-biodegradable substances. For Example - Plastics, glass objects, polythene bags, pesticides, metals such as mercury and lead, radioactive wastes, etc.

Question 4..
Give any two ways in which biodegradable substances would affect the environment.
(CBSE Delhi 2007, AI 2009 C)
Answer:

1. Stink: Within a day or so waste biodegradable substances begin to stink and produce foul gases.
2. Pests and Pathogens: The decaying biodegradable substances become breeding places of flies and many other pests. They also contain a number of pathogens. Flies and other pests carry the germs to all the places visited by them resulting in spread of diseases.

Question 5.
Give any two ways in which non-biodegradable substances would affect the environment. (CBSE AI 2009 C)
Answer:

1. Cause pollution: Dumping of non-biodegradable substances on a piece of land converts the same into barren land. It is also called land pollution.
2. Biological Magnification: Pesticides, heavy metals and other chemicals enter water and food chains. They accumulate in toxic proportions and harm all kinds of living organisms. Their concentration also increases with rise in trophic level. Human beings are harmed the most because man lies at the top of every food chain.

Question 6.
What is ozone and how does it affect the ecosystem ?
Answer:
Definition of Ozone: Ozone is a triatomic molecule made up of three atoms of oxygen, O₃.
Effect:

1. Protection against ultraVoilet rays if present in stratosphere,
2. Ozone dissipates the energy of ultraviolet rays by undergoing dissociation following by reassociation
   

If present in the atmosphere of ecosystem, it is highly toxic causing injury to mucous membranes, eye irritation and internal haemorrhages in animals and humans. It harms plants by destroying photosynthetic cells producing necrosis.

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

Following are the ways to reduce the problem of waste disposal:

• 3 R’s: By following the 3 R’s one can reduce the problem of waste disposal. The 3 R’s are reduce, recycle and reuse. Reducing the usage of their own vehicles and opting for public transport can reduce air pollution. Recycling and reusing of plastics is also a way to reduce waste disposal.
• Preparation of compost: All the biodegradable waste like kitchen waste, can be dumped in the compost.