Does Every Organism in a Community Matter? (12.3) — "How Nature Works in Harmony"

1. 13 marks

   Describe the set-up of the Pond A / Pond B study in Activity 12.3, and its two headline observations.

   Hint. One pond had a predator the other didn't, and that single difference produced two visible contrasts.

   ✦ Researchers compared two ponds: Pond A, which had fish AND a large number of flowering plants nearby, and Pond B, which had no fish and fewer flowering plants nearby. This matters since the two headline observations were that Pond A had fish while Pond B did not, and that Pond A had noticeably more flowering plants around it than Pond B.

2. 23 marks

   Explain, step by step, why Pond A (with fish) had fewer dragonflies than Pond B (without fish).

   Hint. The chain starts with what fish actually eat at the larval stage.

   ✦ 'Fish eat dragonfly larvae, so ponds with fish had fewer dragonflies' — the fish in Pond A directly reduced the dragonfly population by eating their larvae before they could mature, while Pond B, lacking fish, let more dragonfly larvae survive to adulthood.

3. 34 marks

   Trace the full chain of cause and effect from 'Pond A has fish' to 'Pond A has more flowering plants,' explaining each link.

   Hint. Four links: fish eat one thing, that affects a predator, which affects a prey, which affects a plant process.

   ✦ Fish eat dragonfly larvae → fewer dragonflies survive in Pond A → since dragonflies usually eat flies, bees and butterflies, fewer dragonflies means more of these pollinating insects survive → these insects pollinate flowers by moving pollen from one flower to another, which helps plants produce seeds → so flowers near Pond A (with fish) may produce more seeds, and over time, more flowering plants, than those near Pond B (without fish).

4. 43 marks

   What does the Pond A/B study show about how biotic and abiotic components interact, according to the chapter's own conclusion?

   Hint. The chapter names both categories of component explicitly in its summary of the study.

   ✦ 'This study shows how biotic components (fish, dragonflies, pollinators, plants) and abiotic components (temperature, water, nutrients) interact with and affect each other' — demonstrating that a single biotic component (fish) can influence outcomes several steps away (seed production) through a chain of interactions since multiple other biotic and abiotic components are involved together.

5. 53 marks

   The chapter asks: can overfishing by humans change this balance? How might it affect the living and non-living parts of the pond habitat?

   Hint. Reverse the chain you traced for question 3 — what happens if the fish that started the whole chain are removed by humans?

   ✦ If humans overfish Pond A and remove most of its fish, dragonfly larvae would no longer be kept in check, so the dragonfly population would likely rise back up, in turn reducing the population of bees, flies and butterflies that dragonflies prey on. With fewer pollinators, the flowering plants around the pond could see reduced pollination and fewer seeds produced — meaning overfishing, a human action on one biotic component, could disrupt the same chain of interactions the whole activity was built to reveal, ultimately affecting plant reproduction far from the pond itself.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 12 (hecu112.pdf), Reprint 2026-27, pages 190-209. Questions are referenced from the NCERT textbook for identification.