NCERT Solutions For Class 10 Biology: Our Environment

Intext Questions (Page 212)

Question 1: What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Answer-
A trophic level is each step or level of the food chain. Trophic levels represent the various biotic levels in a food chain.

Example of a food chain and its trophic levels:
In a typical terrestrial food chain (like in a grassland), the sequence might be: Grass $\rightarrow$ Goat $\rightarrow$ Human.

1. Grass (Autotroph/Producer): First trophic level.
2. Goat (Herbivore/Primary consumer): Second trophic level.
3. Human (Carnivore/Tertiary consumer, or Omnivore): Third trophic level (if consuming the goat, which is secondary consumption) or Fourth trophic level (if consuming the goat, which is secondary consumption, and the human is the larger carnivore).

Question 2: What is the role of decomposers in the ecosystem?

Answer-
The role of decomposers (microorganisms comprising bacteria and fungi) in the ecosystem is to break-down the dead remains and waste products of organisms. They break down the complex organic substances into simple inorganic substances that go into the soil. These simple inorganic substances are then used up once more by the plants (producers) for replenishment.

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Intext Questions (Page 215)

Question 1: Why are some substances biodegradable and some non-biodegradable?

Answer-
The difference between biodegradable and non-biodegradable substances is due to the specificity of enzymes.

1. Biodegradable substances: These are substances that are broken down by biological processes, such as the action of bacteria or other saprophytes.
2. Non-biodegradable substances: These are substances that are not broken down by the action of specific enzymes produced by bacteria or other saprophytes. Many human-made materials like plastics are non-biodegradable and persist for a long time.

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

Answer-

1. If the rate of decomposition is slow, the accumulation of decaying biodegradable waste can lead to the production of foul smells and harmful gases.
2. Accumulation of such waste can provide a breeding ground for pathogens, insects, and other disease-causing organisms, impacting human and animal health. (Note: While the source implies this issue by discussing decomposer absence, it mainly focuses on the cycling of nutrients. This answer provides two effects on the environment standard for this topic).

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

Answer-

1. Persistence and Harm: Non-biodegradable substances may be inert and simply persist in the environment for a long time. They can harm the various members of the ecosystem, for example, by causing physical harm to animals that consume them or by littering places of tourist interest.
2. Biological Magnification: Some harmful non-biodegradable chemicals (like pesticides) accumulate progressively at each trophic level in the food chain. This phenomenon, known as biological magnification, means their concentration is maximum in organisms (like humans) occupying the top level of the food chain, leading to health risks.

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Intext Questions (Page 216)

Question 1: What is ozone and how does it affect any ecosystem?

Answer-
Ozone ($\text{O}_3$) is a molecule formed by three atoms of oxygen. It is formed at the higher levels of the atmosphere by UV radiation splitting molecular oxygen ($\text{O}_2$) into free oxygen atoms ($\text{O}$), which then combine with $\text{O}_2$.

Effect on the Ecosystem:
At the higher levels of the atmosphere, ozone performs an essential function by shielding the surface of the earth from ultraviolet (UV) radiation from the Sun. Since UV radiation is highly damaging to organisms (e.g., it is known to cause skin cancer in human beings), the ozone layer is vital for protecting the entire ecosystem.

Question 2: How can you help in reducing the problem of waste disposal? Give any two methods.

Answer-
The problem of waste disposal can be reduced by managing the garbage produced, often referred to as the $\text{3 R}$s approach (Reduce, Reuse, Recycle). Two methods include:

1. Reducing the generation of non-biodegradable waste: By making changes in lifestyle, such as carrying cloth-bags for shopping (instead of using disposable plastic bags) and choosing products that are not disposable.
2. Separating waste: Treating the biodegradable and non-biodegradable wastes separately (e.g., burying biodegradable material in a pit for decomposition).

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Exercise Questions (Page 216-217)

Question 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

Answer-
Biodegradable items are those that can be broken down by biological processes. (d) Cake, wood and grass are all substances that are expected to be broken down naturally.
(Option b includes plastic, which is non-biodegradable).

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-
A food chain is a series of organisms feeding on one another, where energy flows from one component to the next. (b) Grass, goat and human is a valid food chain, moving energy from the producer (grass) to the primary consumer (goat) and then to the secondary consumer (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 of the above

Answer-
All options represent practices that reduce waste, conserve energy, or reduce fuel consumption, making them environment-friendly.
The correct option is (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, the entire ecosystem balance would be disturbed.

1. Organisms below the killed level (Previous level): The organisms at the lower trophic level would face an unchecked increase in their population, as their consumers are removed.
2. Organisms above the killed level (Next level): The organisms at the next higher trophic level would die out or face severe hardship due to the lack of food. Since energy flow is unidirectional, the energy from the removed level is no longer available to the next level.

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-
Yes, the impact will be different for different trophic levels.

1. Impact Difference: Removing organisms from lower trophic levels (producers or primary consumers) would likely have a more drastic and widespread impact because they support all subsequent trophic levels (due to the unidirectional flow and loss of energy). For example, removing producers ($\text{T}_1$) would immediately collapse the entire system.
2. Removal Without Damage: No, the organisms of any trophic level cannot be removed without causing damage to the ecosystem. All organisms in an area interact with each other and maintain a balance in nature. Removing any trophic level breaks the food chain, which is essential for the flow of energy and organic matter.

Question 6: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Answer-
Biological magnification is the phenomenon where non-degradable harmful chemicals (like pesticides) that enter the food chain get accumulated progressively at each trophic level.

Levels of Magnification:
Yes, the levels of this magnification will be different at different levels of the ecosystem. Since these chemicals are accumulated progressively, their concentration increases at successive trophic levels. Organisms occupying the top level in any food chain (e.g., human beings) will accumulate the maximum concentration of these chemicals.

Question 7: What are the problems caused by the non-biodegradable wastes that we generate?

Answer-
Non-biodegradable wastes, which persist in the environment for a long time, cause several problems:

1. Environmental Persistence: They remain unchanged over long periods, leading to accumulation and littering of the environment, including public places. Changes in packaging have resulted in much of our waste becoming non-biodegradable.
2. Harm to Ecosystem Members: They may harm the various members of the eco-system. For example, discarded plastics can physically injure or obstruct digestion in animals.
3. Biological Magnification: If the non-biodegradable waste contains harmful chemicals (like pesticides), these chemicals enter the food chain and cause biological magnification, leading to maximum accumulation in top consumers (like humans).

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

Answer-
No, even if all the waste we generate is biodegradable, it will still have an impact on the environment.
Biodegradable substances are broken down by decomposers, but the impact depends on the quantity and rate of disposal:

1. Work Overload: If the amount of waste generated is huge (due to improvements in life-style and large populations), the decomposers may not be able to break down the material quickly.
2. Pollution and Hygiene: A massive accumulation of waste could lead to unhygienic conditions and the waste might pose problems until the decomposition process is complete (e.g., production of foul odours or creation of breeding grounds for pests).

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

Answer-
Cause for Concern:
Damage (depletion) to the ozone layer is a major cause for concern because the ozone layer at the higher levels of the atmosphere performs the essential function of shielding the surface of the earth from ultraviolet (UV) radiation from the Sun. UV radiation is highly damaging to organisms, being known to cause skin cancer in human beings. Increased UV radiation would damage the entire environment.

Steps Taken to Limit Damage:
The depletion of the ozone layer has been linked to synthetic chemicals like chlorofluorocarbons (CFCs). Steps taken to limit this damage include:

1. International Agreement: In 1987, the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels.
2. Mandatory Manufacturing Changes: It is now mandatory for all manufacturing companies to make CFC-free refrigerators throughout the world.