NCERT Solutions for Class 10 Science Chapter 13 Exercise

Answer: Trophic Levels – In a food chain, the transfer of food or energy takes place at various levels and these levels are known as trophic levels.

Example: Grass ⟶ Goat ⟶ Man

In the food chain –
(i) Grass represents the first trophic level
(ii) The goat represents the second trophic level
(iii) Man represents the third trophic level

Answer: Role of decomposers in the ecosystem –
(i) Decomposers help in decomposing the dead bodies of plants and animals and hence act as cleansing agents of the environment.
(ii) Decomposers also help in putting back the various elements of which dead plants and animals are made, back into the soil, air and water for reuse by the producers like crop plants.
(iii) They help in recycling of the nutrients.
(iv) They decompose dead remains thereby providing space for new life to settle in the biosphere.

Answer: Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.

Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.

Answer: Biodegradable substances would affect the environment in these two ways –
(i) During the decomposition process of biodegradable substances, foul smell and some harmful gases are released which cause problems for the nearby living person.
(ii) During the decomposition, it provides a breeding ground for mosquitoes, insects and microbes responsible for diseases like cholera, diarrhea, etc.

Answer: Non-biodegradable substances would affect the environment in these two ways –
(i) They contaminate soil and water resources as they can’t be rotten by microorganisms.
(ii)These substances, if accidentally eaten by stray animals, will damage them and might even cause their death.

Answer: Ozone is an isotope of oxygen. At the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the sun. These radiations are highly damaging to organisms. Ultraviolet rays can cause skin cancer.

Answer: Following are the ways to reduce the problem of waste disposal –
(i) 3 R’s :- One can reduce the problem of waste disposal by following the 3 R’s. They 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.
(ii) Preparation of compost :- All the biodegradable waste like kitchen waste, can be dumped in the compost.

Answer: (c) Fruit-peels, cake and lime-juice , and

(d) Cake, wood and grass

Answer: (b) Grass, goat and human

Answer: (d) All of the above

Answer: If we kill all the organisms in one trophic level, the food supply to the next level will stop. This will cause an imbalance of the ecosystem. As a result, the animals in the higher trophic levels will die while the animals in the lower trophic level will multiply. All of this will affect the overall balance in the ecosystem.

Answer: Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels. For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can’t remove any trophic level without causing damage to the ecosystem as one is dependent on the other for their survival. If we remove any one this will create imbalance in the ecosystem.

Answer: Biological Magnification – 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.

Yes, levels of bio-magnification would increase as the trophic level increases and would be the highest for the topmost trophic level. It would affect their biological processes such as growth, reproduction, etc.

Answer: Problems caused by the non-biodegradable wastes –
(i) These substances cannot be decomposed by the microorganisms.
(ii) As the quantity increases, dumping becomes a problem.
(iii) Non-biodegradable wastes like heavy metals may enter the food chain in the upper trophic levels.
(iv) They may escape to the groundwater which causes soil infertility and disturbance in pH of the soil.

Answer: Biodegradable wastes are decomposed by microorganisms into simpler substances themselves and provide raw materials for producers, but they also have adverse effects on the environment –

(i) Slow decomposition of biodegradable waste will result in the release of foul smell and harmful gases. When inhaled by human beings, they may cause irritation, nausea, giddiness, etc.

(ii) Decomposing waste provides breeding ground for some harmful organisms.
Abundance of harmful microorganisms may cause diseases in animals, plants and human beings.

(iii) Increase in the number of microorganisms in aquatic mediums will- cause oxygen deficiency in water bodies.

Answer: The ozone layer is the protective layer of the earth from harmful rays. It plays a significant role in protecting all living and nonliving organisms. If a layer is broken, no organism will survive. Following measures are being taken to limit this harm —

(i) We must always minimize the employment of vehicles.
(ii) We must always not encourage the burning of fossil fuels.
(iii) It’s currently necessary for all the producing firms to form CFC- free refrigerators throughout the globe.