NCERT Solutions Curiosity Chapter 12 –19512.3 Does Every Organism in a Community Matter? — Activity 12.3: Let us read

Book page 194 Updated on2026-09-05

Q1.

Researchers conducted a study to see how fish in ponds affect seed production in the plants nearby. They observed two ponds — A with fish and large number of flowering plants around it; B without fish and fewer flowering plants around it (Fig. 12.3). Think of a reason for these observations.

Answer

A likely reason: the fish are not affecting the plants directly at all — they are affecting the insects that pollinate them.

Trace the links. Fish eat dragonfly larvae, which live in the water. Dragonflies (the adults) eat flies, bees and butterflies, which live in the air above the pond and visit the flowers around it. So:

Pond A: fish present → fewer dragonfly larvae → fewer dragonflies → more bees, flies and butterflies → more pollination → more seeds
Pond B: no fish → dragonfly larvae survive → more dragonflies → fewer bees and butterflies → less pollination → fewer seeds

That is why pond A has a large number of flowering plants around it and pond B has fewer.

Tip: this is what Fig. 12.4 shows. The red arrows are direct effects (fish on larvae, dragonfly on bee); the green arrows are indirect effects (fish on bees, fish on the plant). An indirect effect works through a third organism.

Q2.

Compare the number of dragonflies, bees, and butterflies in both the ponds. Do you find any relationship between the number of dragonflies and bees/butterflies? We observed that in Pond A (with fish) the number of dragonflies were less as compared to Pond B. Why?

Answer

Yes — the relationship is inverse. Where dragonflies are many, bees and butterflies are few; where dragonflies are few, bees and butterflies are many.

	Pond A (with fish)	Pond B (without fish)
Dragonflies	Fewer	More
Bees, flies, butterflies	More	Fewer
Seeds set by nearby flowers	More	Fewer

Pond A has fewer dragonflies because fish eat dragonfly larvae. The dragonfly spends its early life in the water as a larva, and that is exactly where the fish can reach it. Fewer larvae survive, so fewer adult dragonflies emerge into the air.

Why it happens: the dragonfly is a predator of bees and butterflies. Take away a predator and its prey increases — so bees, flies and butterflies become more common in pond A. This is the same rule you will use again in Question 4 of Keep the curiosity alive, where frogs disappear from a food chain.

Q3.

What does this study show? How does the population of fish in a pond affect the seed production in nearby plants?

Answer

It shows that organisms in a community are connected even when they never meet — and that a change in one population can travel through the community to reach a completely different kind of organism.

A fish never touches a flower. Yet the number of fish in the pond decides the number of seeds the flowers set, through a chain of three steps:

More fish → fewer dragonfly larvae
→ fewer adult dragonflies
→ more bees, flies and butterflies
→ more pollen carried from flower to flower
→ more seeds produced

The study also shows that biotic components (fish, dragonflies, pollinators, plants) and abiotic components (temperature, water, nutrients) interact with and affect each other. So the answer to the section's title question — does every organism in a community matter? — is yes: each one is a link that something else depends on.

Did you know? An effect that passes through another organism, like the fish's effect on the flowers, is called an indirect effect. Indirect effects are often stronger than the direct ones, and they are the reason removing a single species can change an ecosystem in ways nobody expected.

Q4.

Similarly, can overfishing by humans change this balance? How do you think it may affect the living and non-living parts of the habitat?

Answer

Yes. Overfishing removes the fish, so the whole chain in Fig. 12.4 runs the other way.

Effect on the living parts:

Fewer fish → more dragonfly larvae survive → more adult dragonflies
→ fewer bees, flies and butterflies
→ less pollination → fewer seeds and fruits on the plants around the pond
→ fewer plants in the next season → less food and shelter for other pond animals

Fish are also consumers of small pond animals and of algae. With the fish gone, mosquito larvae and other insects can multiply unchecked, and algae can spread over the surface.

Effect on the non-living parts: a thick mat of algae cuts off sunlight to the plants below. Those plants die, and dying plants mean less oxygen produced in the water. Decomposing the dead material uses up more oxygen still. So the water itself — an abiotic component — becomes poorer, cloudier and lower in oxygen, and the whole habitat is harder to live in.

Why it happens: the balance of an ecosystem is dynamic, not fixed. It is held by the interactions among organisms, not by any one organism. Taking out a whole population at once removes several interactions together, and the ecosystem settles into a new and usually poorer state.

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