NCERT In Text Solution
Question 1: Why are some substances biodegradable and some non-biodegradable?
Answer: Substances which are of organic origin are biodegradable, while those of inorganic origin are non-biodegradable. Organic substances can be utilised by decomposers as food, while other substances cannot be utilised by decomposers as food. Due to this, some substances are biodegradable while some others are non-biodegradable.
Question 2: Give any two ways in which biodegradable substances would affect the environment.
Answer: Biodegradable substances can affect the environment in following ways:
- By recycling the raw materials in nature.
- By improving the humus content in soil.
Question 3: Give any two ways in which non-biodegradable substances would affect the environment.
Answer: Non-biodegradable substances would affect the environment in following two ways:
- By increasing the burden on the environment because they would accumulate.
- By producing harmful polluting gases, if they are burnt.
Question 4: What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer: A particular level in a food chain is called trophic level. Following example shows trophic levels in a food chain:
Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer
Grass → Grasshopper → Frog → Snake
Question 5: What is the role of decomposers in the ecosystem?
Answer: Decomposers decompose dead remains of plants and animals. By doing so, they serve two purposes. One; they reduce the burden on the environment by clearing dead remains. Two; they channelize the raw materials back to the environment.
Question 6: What is ozone and how does it affect any ecosystem?
Answer: Ozone is a form of oxygen. Ozone is a triatomic molecule while oxygen is a diatomic molecule. Ozone forms the ozone layer in our atmosphere. Ozone plays an important role in the ecosystem. The ozone layer wards off harmful ultraviolet radiations from the sun and thus protects the living beings.
Question 7: How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: The problem of waste disposal can be reduced in many ways. Two methods are given below:
- By using more of biodegradable substances and reducing the use of non-biodegradable substances. For example; instead of plastic bags, one should carry jute bags or cloth bags for shopping.
- By proper segregation of waste before disposing.
Solution of NCERT EXERCISE
Question 1: Which of the following groups contain only biodegradable items?
- Grass, flowers and leather
- Grass, wood and plastic
- Fruit-peels, cake and lime-juice
- Cake, wood and grass
Answer: (c) and (d)
Question 2: Which of the following constitute a food-chain?
- Grass, wheat and mango
- Grass, goat and human
- Goat, cow and elephant
- Grass, fish and goat
Answer: (b)Grass, goat and human
Question 3: Which of the following are environment-friendly practices?
- Carrying cloth-bags to put purchases in while shopping
- Switching off unnecessary lights and fans
- Walking to school instead of getting your mother to drop you on her scooter
- All of the above
Answer: d. All of the above
Question 4: What will happen if we kill all the organisms in one trophic level?
Answer: If all the organisms in one trophic level are killed, it will disturb the whole ecosystem. Let us take a hypothetical example to understand this. If all the deer are killed in a jungle, the lions would be left with no food. This would endanger the existence of lions. Once the lions and deer would be finished, it would result in population explosion of green plants. If all the lions die in a jungle, it would create another problem. Since no lion would be left to kill the deer, the population of deer would increase substantially. This will finish off all the green plants and finally even the deer would be left with no food for them.
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: The impact of removing all the organisms in a trophic level shall be similar for different trophic levels; although their manifestations can be different. Organisms of any trophic level cannot be removed without causing any damage to the ecosystem. The examples of lions and deer in the previous answer illustrate this.
Question 6: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: The accumulation of a particular substance through different trophic levels is called biological magnification. Let us take example of lead poisoning which may affect plants because of water pollution. The level of lead would be at a particular level in plants. When an herbivore would eat these plants, the level of lead shall be more in the body of herbivore because it would eat a large number of plants. When this herbivore would be eaten by a carnivore, the level shall rise further because the carnivore would eat a large number of herbivores. Hence, the level of this magnification will increase as we move to higher trophic levels.
Question 7: What are the problems caused by the non-biodegradable wastes that we generate?
Answer: Non-biodegradable waste creates many problems. Biodegradable waste keeps on accumulating in the environment because it does not decompose. Hypothetically, a time may come when the whole earth would be filled with non-biodegradable waste. If we try to destroy such waste by way of burning, it would create many polluting gases.
Question 8: If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer: If all the waste we generate is biodegradable, this would also have an impact on the environment but most of the impacts would be positive. After decomposition, the biodegradable substance produces different raw materials which are sent back to the ecosystem. The solid remains would add to the humus content of soil.
There can be some negative impacts; like obnoxious smell which is created during the process of decomposition. There can also be a possibility of sparking an epidemic if the waste is dumped near a residential area or is allowed to contaminate the water bodies. So, it is not the biodegradable waste which is going to create the problem, rather the way we dispose it.
Question 9: Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer: Ozone layer works like a protective shield for living beings. The ozone layers wards off harmful ultraviolet radiations from the sun. Damage to the ozone layer can result in increased level of ultraviolet radiations in our atmosphere. This would be very dangerous for all life forms.
In 1987, the UNEP (United Nations Environment Programme) succeeded in forging an agreement among different nations to freeze the CFC production at 1986 level. Later, an agreement was signed among different nations to phase out CFCs. It is important to note that CFC is used in refrigerators and aerosol spray. India is also a signatory of that agreement and thanks to the efforts by the United Nations and different environmentalists, the CFC emission has been put under some control.