Class 10 Science Chapter 13: Important & Previous Year Questions – Bihar Board

Correct answer: (D) Both (A) and (B)

Bacteria and fungi break dead organisms and waste into simple inorganic substances — they are decomposers (micro-consumers). Algae are green, so they are producers (lesson 1).

Correct answer: (B) Secondary consumer

Herbivores = primary consumers. The carnivores that eat them = secondary consumers (large carnivores can also sit at the tertiary level, but the expected answer here is (B)). (A) is wrong, so (D) is wrong too (lesson 2).

Correct answer: (C) 10%

Ten percent law: on average only about 10% of the food eaten becomes the body of the next level; the rest goes in heat, digestion and work (lesson 2).

• The next level gets no food — it starves or declines.
• The organisms of the previous level increase (e.g. remove carnivores → herbivores rise and plants fall).
• The flow of energy breaks and the ecosystem loses its balance. Remove the producers and the whole chain collapses (lesson 7, NCERT exercise 4).

• Source: the Sun. Green plants (producers) turn about 1% of the sunlight on their leaves into food (chemical energy) by photosynthesis.
• Energy moves along the food chain: producer → herbivore (primary consumer) → small carnivore (secondary) → large carnivore (tertiary). Example: grass → grasshopper → frog → snake.
• Ten percent law: at each level only ~10% of the food eaten becomes the body of the next level; the rest is spent as heat, in digestion and in work.
• So chains usually have 3–4 steps, and the lowest level has the most organisms.
• The flow is one-way — energy passed to herbivores does not return to plants, nor plant energy to the Sun.
• Decomposers return matter to the soil (matter cycles, energy does not).

Correct answer: (A) Dead grass and leaves

Dead grass and leaves are biodegradable — bacteria and fungi break them down. Polythene is non-biodegradable (lesson 5).

Correct answer: (D) All of these

The environment is everything around organisms — water, land (soil, minerals) and air; these are the abiotic components of an ecosystem (lesson 1).

Correct answer: (B) Secondary

Grass → grasshopper (primary) → frog (secondary consumer) → snake (tertiary) (lesson 2).

Correct answer: (A) DDT

Pesticides like DDT are not broken by organisms — they collect in the food chain by biological magnification. Paper and sewage are biodegradable (lessons 3, 5).

Organisms that make their own food — sugar and starch — from inorganic substances (CO₂, water) using sunlight and chlorophyll are producers. Examples: all green plants and certain bacteria. They form the first trophic level of a food chain and bring energy into the whole ecosystem (lessons 1, 2).