Q1. [5] deep thorough-understanding
Consider a simple food chain: Grass → Grasshopper → Frog → Snake → Hawk.
(i) At which trophic level would biological magnification of a non-biodegradable pesticide be the highest, and why?
(ii) If the frog population is entirely wiped out, predict two consequences for the ecosystem, one for the trophic level below and one for the trophic level above.
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
(i) Trophic Level with Highest Biological Magnification:
The 5th trophic level (Hawk) would have the highest concentration of the non-biodegradable pesticide. Since these chemicals are not broken down, they accumulate progressively at each trophic level. By the time they reach the top consumer (hawk), the concentration is the greatest. This phenomenon is called biological magnification.
(ii) Two Consequences if Frog Population is Wiped Out:
- Effect on trophic level below (Grasshopper): Without frogs to prey on them, the grasshopper population would increase enormously. This would lead to overgrazing of grass, destroying vegetation and destabilising the ecosystem.
- Effect on trophic level above (Snake): Snakes would lose their primary food source. The snake population would decline sharply due to starvation, which would further affect hawks at the next level.
Source: Chapter 13, Section 13.1.1 – Food Chains and Webs
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Explanation
- Part (i): Examiners expect you to name the correct trophic level (hawk/5th), state the principle that non-biodegradable chemicals accumulate and are not excreted, and use the term biological magnification.
- Part (ii): One consequence must address the level below (grasshoppers increase → grass depleted) and one must address the level above (snakes decline). Both directions must be covered for full marks. Keep each point crisp — one cause-effect sentence each.
- Avoid vague answers like "the ecosystem will be disturbed"; be specific about which population rises or falls and why.