NCERT Class X Science Class: Chapter –15. Our Environment – Part-5

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Question 27:

Suggest one word for each of the following statements/ definitions

(a) The physical and biological world where we live in

(b) Each level of food chain where transfer of energy takes place

(c) The physical factors like temperature, rainfall, wind and soilof an ecosystem

(d) Organisms which depend on the producers either directly orindirectly for food


(a) Environment/biosphere

(b) Trophic level

(c) Abiotic factors

(d) Consumers/heterotrophy

Question 28:

Explain the role of decomposers in the environment?


Various role played by decomposers in the ecosystem are:They clean the environment.→ They decompose biodegradable substances into useful substances.→ They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.→ They maintain the nutrient pool by returning back the nutrients in the pool.

Question 29:

Select the miss-matched pair in the following and correct it.

(a) Bio magnification — Accumulation of chemicals at the successive trophic levels ofa food chain

(b) Ecosystem — Biotic components of environment

(c) Aquarium — A man-made ecosystem

(d) Parasites — Organisms which obtain food from other living organisms


(b) Is not a matching pair

Both biotic and abiotic components of environment constitutean ecosystem

Question 30:

We do not clean ponds or lakes, but an aquarium needs to becleaned. Why?


An aquarium is an artificial and incomplete ecosystem in contrastto a pond/lake which are natural, self-sustaining and complete ecosystems. Aquarium is an artificial ecosystem, which contain fishes as living organisms. In natural ecosystems, other organisms are also present in sufficient number to maintain a balance.

In natural aquatic ecosystem, uneaten food or fish waste turns into ammonia, bacteria then convert these pollutants into non-toxic nitrates. So, If water of aquarium is not changed regularly then wastes could accumulate to dangerous level, that fishes could even die.

Long Answer Questions

Question 31:

Indicate the flow of energy in an ecosystem. Why is it unidirectional?Justify.


Image Flow of energy in an ecosystem

Image Flow of Energy in an Ecosystem

Image Flow of energy in an ecosystem

The flow of energy in the ecosystem is unidirectional. The energy enters the plants (from the sun) through photosynthesis during the making of food. This energy is then passed on from one organism to another in a food chain.

Energy given out by the organisms as heat is lost to the environment, it does not return to be used by the plants again. This makes the flow of energy in ecosystem ‘unidirectional’. Thus, the flow of energy in the ecosystem is said to be unidirectional because the energy lost as heat from the living organisms of a food chain cannot be reused by plants in photosynthesis.

During the transfer of energy through successive trophic levels in an ecosystem, there is a loss of energy all along the path. No transfer of energy is 100 per cent. The energy available at each successive trophic level is 10 per cent of the previous level. Thus, there is a progressive decline (gradual reduction) in the amount of energy available as we go from producer level to the higher trophic levels of organisms.

The nutrient movement is a cyclic movement where the nutrients revolve round with an ecosystem, hence cyclic. Nutrients pass from abiotic nutrient stores, such as the soil and the atmosphere, into biotic, plant and animal stores (the biomass). The nutrients are then recycled, within the ecosystem, following death and decomposition.

Question 32:

What are decomposers? What will be the consequence of their absence in an ecosystem?


Decomposers or saprotrophs are organisms that break down dead or decaying organisms, and in doing so carry out the natural process of decomposition. if there were no decomposers in the ecosystem then there would be no organic nutrients and all dead plants and animals would ruin the animal habitat. The ecosystem will be filled with plants and animals waste.

Image Fossills and fossil fuels

Image Fossills and Fossil Fuels

Image Fossills and fossil fuels

Question 33:

Suggest any four activities in daily life which are eco-friendly.


(i) Separation of biodegradable and non-biodegradable substances.(ii) Gardening(iii) Use of gunny bags/paper bags in place of polythene/plastic bags(iv) Use of compost and vermin compost in place of fertilizers(v) Harvesting rainwater