Chapter 13 · Our Environment

NCERT Class 10 Science Chapter 13 Intext Questions (Page 212)

All 2 questions of NCERT Class 10 Science Chapter 13 Intext Questions (Page 212) — Our Environment — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   What are trophic ​levels? Give ​an example ​of ​a food chain and ​state the different trophic levels ​in it.
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   A trophic level is a step of a food chain; in Grass → Grasshopper → Frog → Snake the four levels are producer, herbivore and two carnivores.

   Each step or level of a food chain at which food, and the energy in it, is transferred from one organism to the next is called a trophic level. The organisms of a food chain are placed at these levels according to how they get their food: the autotrophs or producers are at the first trophic level, the herbivores or primary consumers at the second, the small carnivores or secondary consumers at the third, and the larger carnivores or tertiary consumers at the fourth. Example of a food chain in a grassland: Grass $\to$ Grasshopper $\to$ Frog $\to$ Snake. Its trophic levels are: first trophic level, grass, the producer, which fixes solar energy by photosynthesis; second trophic level, grasshopper, a herbivore and primary consumer; third trophic level, frog, a small carnivore and secondary consumer; fourth trophic level, snake, a larger carnivore and tertiary consumer. Only about ten per cent of the energy at each level reaches the next, so a chain of this kind rarely runs beyond three or four trophic levels.

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2. Q2
   What ​is the role ​of ​decomposers ​in the ecosystem?
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   Decomposers break dead remains and waste into simple inorganic substances that return to the soil, so nutrients are recycled and the environment stays clean.

   Decomposers are microorganisms, mainly bacteria and fungi, that live on the dead remains and waste products of other organisms, and they have three linked roles in an ecosystem. First, they break down the complex organic substances of dead plants, dead animals and excreta into simple inorganic substances, a job no producer or consumer performs. Second, these simple substances go back into the soil, water and air, where the producers absorb them once more through their roots and build them into new organic matter, so the nutrients of the ecosystem are recycled and the fertility of the soil is naturally replenished; energy flows through an ecosystem in one direction and is lost as heat, but matter is used over and over, and it is the decomposers who close that loop. Third, by clearing away dead bodies, dead plant parts and waste, they keep the environment clean and leave room for new growth. If they were absent, dead matter would pile up and the nutrients locked inside it would never return to the soil, so the producers would run short of raw material and the whole ecosystem would run down.

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