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Class 8 Science: How Nature Works in Harmony, 8 practice questions with answers

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These are 8 practice questions on the twelfth chapter of the new NCERT Class 8 Science textbook, Curiosity, called How Nature Works in Harmony. Each has a short answer and the textbook page it comes from. They cover biotic and abiotic components, populations, communities and ecosystems, how plants change the non-living parts of a habitat, producers and consumers, food chains and trophic levels, decomposers in a compost pit, competition, and three kinds of relationship. For the start of this topic in the Class 6 book, see our Class 6 Diversity in the Living World guide. Try each question before you read the answer.

These questions are our own, drafted with AI help. Every fact was checked against the page it cites by a test script, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Curiosity, Grade 8, Chapter 12, printed pages 190 to 209):

Living and non-living parts

Question 1. In a paddy field, sort these into biotic and abiotic components: rice plants, earthworms, sunlight, soil, frogs, water, temperature, fungi.

Answer: biotic: rice plants, earthworms, frogs, fungi; abiotic: sunlight, soil, water, temperature. The biotic components are the living beings of a habitat: plants, animals and microorganisms such as fungi. The abiotic components are the non-living things and conditions: air, sunlight, water, temperature and soil. (Biotic and abiotic components, pages 192 and 193.)

Question 2. In a lake, name the level for each: (a) one heron; (b) all the herons living in the lake now; (c) the herons, fish, lotus plants, algae and microbes of the lake together; (d) all of these together with the lake's water, mud, air and sunlight.

Answer: (a) an individual; (b) a population; (c) a community; (d) an ecosystem. (a) A single organism is an individual. (b) A group of the same kind of organism living in a habitat at a given time is a population. (c) The different populations sharing the same habitat make up a community. (d) The biotic components and the abiotic components interacting with each other form an ecosystem. (Population, pages 193 and 194; community, page 194; ecosystem and the levels from individual to ecosystem, page 197.)

Question 3. A bare, sloping patch of ground beside a school is planted with grass, shrubs and trees. Using the chapter, give three ways in which these plants can change the non-living parts of the patch.

Answer: for example, they add oxygen to the air, their roots hold the soil, and they keep the soil moist and the air cooler. Living things do not only depend on the abiotic components; they also change them. (1) Plants give out oxygen into the air when they make food by photosynthesis. (2) Their roots hold the soil in place, so rain is less likely to wash the slope away (erosion). (3) Plants help the soil keep its moisture and help cool the air around them. (Biotic components influencing abiotic ones, page 197.)

Who eats whom

Question 4. Classify each as a producer, a herbivore, a carnivore, an omnivore or a decomposer: a neem tree, a goat, a kingfisher (which eats fish), a crow, a mushroom on a dead log. Which of them are autotrophs?

Answer: neem tree, producer; goat, herbivore; kingfisher, carnivore; crow, omnivore; mushroom, decomposer. Only the neem tree is an autotroph. Plants make their own food by photosynthesis, so they are producers or autotrophs ("self-feeding"). The other four have to get their food by eating other living things or their remains, so they are heterotrophs. A goat eats only plants (herbivore), a kingfisher eats only animals (carnivore), and the chapter names crows among the animals that eat both (omnivores). A mushroom is a fungus that grows on dead matter and breaks it down: a decomposer. (Producers and consumers, page 198; decomposers, pages 200 and 201.)

Question 5. In a pond, algae are eaten by small water insects, the insects are eaten by fish, and the fish are eaten by a kingfisher. (a) Write the food chain. (b) Give the trophic level of each organism. (c) The fish are also eaten by herons. What do the linked food chains of the pond then form?

Answer: (a) algae → water insects → fish → kingfisher; (b) algae first, insects second, fish third, kingfisher fourth; (c) a food web. (a) A food chain shows who eats whom, with the arrow pointing to the eater. (b) Producers, here the algae, are at the first trophic level; the plant-eating insects at the second; the fish, a small carnivore, at the third; and the kingfisher at the fourth. (c) When the fish are eaten by herons as well as by the kingfisher, the chains are joined, and food chains linked together in this way form a food web. (Producers, page 198; food chains and trophic levels, pages 199 and 200.)

Question 6. A gardener puts fallen leaves, dead plants and vegetable peels into a pit and leaves them there. Some months later the pile has turned into dark, crumbly earth. (a) Which kinds of living things did this work, and what are such organisms called? (b) What did they give back to the soil?

Answer: (a) microorganisms such as fungi and bacteria, with small animals such as beetles; they are decomposers (saprotrophs); (b) nutrients. (a) Fungi and bacteria break the complex materials of dead plants into simpler substances, and small creatures such as beetles and flies help break dead matter and droppings down too. This is decomposition, and the organisms that carry it out are decomposers, also called saprotrophs ("feeding on rotten matter"). (b) Decomposition returns important nutrients to the soil, and many of the nutrients plants take from the soil come from it, so the gardener's plants can use them again. (Decomposition, pages 200 and 201.)

Balance in nature

Question 7. In a vegetable plot, spinach plants and several kinds of weeds grow close together. (a) What do they compete for? (b) According to the chapter, how does competition help an ecosystem?

Answer: (a) sunlight, water and space; (b) it keeps any one kind from multiplying too much. (a) Besides feeding relationships, organisms compete for common resources such as food, water, physical space and sunlight; plants in one plot compete for light, water and space. (b) Competition helps control the size of populations. If there were no competition, a single kind of plant or animal could grow far too numerous and tip the ecosystem out of balance. (Competition and balance, page 202.)

Question 8. Using the chapter's three kinds of relationship, name the kind in each case below and say who benefits. None of these examples is in the chapter. (a) Cattle egrets walk beside grazing cows and eat the insects the cows stir up from the grass; the cows are neither helped nor harmed. (b) A mistletoe plant grows on a tree and takes water and minerals from it, weakening the tree. (c) A clownfish shelters among the stinging arms of a sea anemone and keeps the anemone clean, and both gain.

Answer: (a) commensalism; (b) parasitism; (c) mutualism. The chapter defines three kinds: in mutualism both organisms benefit; in commensalism one benefits and the other is not affected; in parasitism one benefits and the other is harmed. (a) The egret gets food and the cow is unaffected: commensalism. (b) The mistletoe benefits and the tree is harmed: parasitism. (c) Both the clownfish and the anemone gain: mutualism. (Kinds of relationships, page 203; the three examples and their details are from outside the chapter, as the question says.)

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Sources

All opened and read on 2 November 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 189 for this chapter.

The facts are from the textbook pages above. The questions, answers and checks are our own. This guide is general information; follow your teacher and the textbook.