CBSE Important Questions Class 8 Science Chapter 12 – How Nature Works in Harmony

Class 8 Science Chapter 12 How Nature Works in Harmony is part of the new NCERT Curiosity textbook. It explains how living things and their surroundings are linked together in an ecosystem. Students learn about producers, consumers and decomposers, food chains and food webs, trophic levels, and the different ways in which organisms live together, such as mutualism, commensalism, parasitism and competition.

These CBSE important questions for Class 8 Science Chapter 12 cover the difference between a food chain and a food web, herbivores, carnivores and omnivores, the role of decomposers, migratory birds linking distant ecosystems, why numbers fall as we go up the trophic levels, honeybees and flowers as an example of mutualism, and biotic and abiotic components. Every question has a clear step-by-step answer in simple English, so students can practise on their own, parents can check the answers, and teachers can use them for class tests.

Q1. Choose the correct statement about food chains and food webs.
(a) Food chains show all possible feeding relationships in an ecosystem
(b) Food webs are simpler than food chains
(c) Food chains and food webs are identical concepts
(d) Food webs show interconnected food chains where organisms may be eaten by multiple predators

Answer: (d) Food webs show interconnected food chains where organisms may be eaten by multiple predators
A food chain is only a single straight line of who eats whom. In real nature most animals eat more than one kind of food and are eaten by more than one predator, so many food chains cross one another and form a food web. A web is therefore more complex than a chain, not simpler.

Q2. Fill in the blanks.
(a) Organisms that eat only plants are called _______, those eating only animals are _______, and those eating both are omnivores.
(b) In mutualism _______ organisms benefit, in commensalism one benefits while the other is _______.
(a) herbivores, carnivores; both, unaffected
(b) consumers, producers; all, helped
(c) autotrophs, heterotrophs; some, destroyed
(d) carnivores, herbivores; none, affected

Answer: (a) herbivores, carnivores; both, unaffected
Animals that eat only plants are herbivores (cow, deer), and those that eat only other animals are carnivores (lion, snake). In mutualism both partners gain something, as with the bee and the flower. In commensalism one gains while the other is neither helped nor harmed, as when an orchid grows on the branch of a tree.

Q3. Read the statement and choose the correct option.
Decomposers occupy the highest trophic level in food chains because they break down organisms from all other levels.
(a) True – decomposers are at the top
(b) True – decomposers eat everything
(c) False – only carnivores occupy high trophic levels
(d) False – decomposers work on all levels but are not part of the linear trophic hierarchy

Answer: (d) False – decomposers work on all levels but are not part of the linear trophic hierarchy
Decomposers such as bacteria and fungi break down the dead bodies and waste of producers, herbivores and carnivores alike. Since they act on every level rather than feeding at one particular step, they are not placed at the top of the chain. They are better seen as working alongside the whole chain, returning nutrients to the soil.

Q4. Migratory birds fly thousands of miles to India to avoid a harsh climate and search for food. They act as pollinators and seed dispersers along their path. What does this illustrate about ecosystem interactions?
(a) Climate has no role in species distribution
(b) Only local organisms affect ecosystem balance
(c) Migration links distant ecosystems through pollination
(d) Birds do not interact with ecosystems they pass through

Answer: (c) Migration links distant ecosystems through pollination
As the birds travel, they carry pollen and seeds from one region to another. In this way plants far apart are connected, and the ecosystems along the whole route depend on one another. It shows that an ecosystem is not a closed box; events in one place can affect life thousands of kilometres away.

Q5. In a grassland food chain (Grass → Grasshopper → Frog → Snake → Eagle) students counted 10,000 grass plants, 1,000 grasshoppers, 100 frogs, 10 snakes and 1 eagle. What pattern does this demonstrate?
(a) All trophic levels have equal populations
(b) Population decreases as we move up trophic levels
(c) Carnivores are more numerous than producers
(d) Trophic levels do not affect population size

Answer: (b) Population decreases as we move up trophic levels
At each step of the chain, only a small part of the energy, about ten per cent, passes on to the next level; the rest is used up by the organism itself or lost as heat. With less energy available, fewer organisms can be supported, so the numbers fall sharply as we move from grass to eagle. This pattern is called the pyramid of numbers.

Q6. Honeybees visit flowers and collect nectar for food, and during this process pollen sticks to their bodies and is transferred to other flowers, helping pollination. Both organisms benefit. What type of interaction is this?
(a) Competition – both need the same resource
(b) Commensalism – only the bee benefits
(c) Parasitism – the bee harms the flower
(d) Mutualism – both organisms benefit

Answer: (d) Mutualism – both organisms benefit
The bee gets nectar as its food, and the plant gets its pollen carried to another flower so that seeds can form. Since both partners gain and neither is harmed, this is mutualism. It is one of the best known examples of two very different living things depending on each other.

Q7. Read the Assertion (A) and Reason (R) and choose the correct option.
Assertion (A): Decomposers are essential for ecosystem functioning.
Reason (R): Decomposers return nutrients to the soil by breaking down dead plants and animals.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Answer: (a) Both A and R are true and R is the correct explanation of A
Decomposers break down dead bodies and waste into simple substances, which go back into the soil. Plants take up these nutrients again and the cycle continues. Without this recycling the soil would lose its fertility and dead matter would pile up, so the Reason is exactly why decomposers are essential.

Q8. Read the Assertion (A) and Reason (R) and choose the correct option.
Assertion (A): A food chain shows a linear sequence of 'who eats whom' in an ecosystem.
Reason (R): Food webs are interlinked to form food chains because each organism may be eaten by multiple types of organisms.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Answer: (c) A is true but R is false
The Assertion is correct: a food chain really is a straight-line sequence of who eats whom. But the Reason states things the wrong way round. It is the food chains that link together to form a food web, not the other way about.

Q9. Organisms that make their own food through photosynthesis are called ___________.
(a) Consumers or heterotrophs
(b) Decomposers or saprotrophs
(c) Producers or autotrophs
(d) Carnivores

Answer: (c) Producers or autotrophs
Green plants and algae use sunlight, carbon dioxide and water to make their own food, so they are called autotrophs. Since they produce the food on which every other organism depends, they are also called producers and they always form the first level of a food chain.

Q10. In a study, ponds with fish had fewer dragonflies, more bees and butterflies, and more flowering plants nearby. What does this demonstrate?
(a) Fish directly help flowers grow
(b) Dragonflies prevent flower growth
(c) Bees and butterflies compete with fish
(d) Indirect effects – fish eat dragonfly larvae, so there are fewer dragonflies

Answer: (d) Indirect effects – fish eat dragonfly larvae, so there are fewer dragonflies
The fish eat the dragonfly larvae in the water, so fewer adult dragonflies grow up. Dragonflies hunt bees and butterflies, so with fewer dragonflies about, more bees and butterflies survive. More pollinators mean better pollination and more flowering plants. The fish never touch the flowers, yet they affect them through this chain of links, which is called an indirect effect.

Q11. Differentiate between a food chain and a food web.

Q12. Name the following.
(a) The term for living organisms in a habitat.
(b) The term for non-living components like water, soil and sunlight in a habitat.

Answer: (a) Biotic components. These are all the living things in a habitat, such as plants, animals, fungi and bacteria.
(b) Abiotic components. These are the non-living things, such as water, soil, air, sunlight and temperature.
Together the biotic and abiotic components make up an ecosystem, and the two keep influencing each other all the time.

Related Study Material on Extramarks

• CBSE Important Questions Class 8 Science Chapter 1
• CBSE Important Questions Class 8 Science Chapter 2
• CBSE Important Questions Class 8 Science Chapter 3
• CBSE Important Questions Class 8 Science Chapter 4
• CBSE Important Questions Class 8 Science Chapter 5
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