Q1. [3] medium thorough-understanding
Explain the process of biological magnification. A non-degradable pesticide was detected at a concentration of 0.1 ppm in the water of a pond. Arrange the following organisms in the order of increasing pesticide concentration in their bodies, and justify your answer: large fish, water plants, small fish, fish-eating birds.
Generated by claude-sonnet-4-6 · 2026-06-26 00:59 · grounding rag
Model Answer
Biological Magnification: The accumulation of non-degradable chemicals (like pesticides) at each successive trophic level in a food chain is called biological magnification. Since these chemicals cannot be broken down, their concentration increases as we move up the food chain.
Order of increasing pesticide concentration:
Water plants → Small fish → Large fish → Fish-eating birds
Justification: Water plants absorb the pesticide (0.1 ppm) from water. Small fish eat many plants, accumulating higher concentrations. Large fish eat many small fish, concentrating it further. Fish-eating birds are at the highest trophic level and thus have the maximum pesticide concentration.
Source: Chapter 13, Our Environment
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Explanation
- Examiners expect: (1) a one-line definition of biological magnification, (2) the correct sequence, and (3) a brief justification linked to trophic levels.
- The key phrase is non-degradable — these substances are not broken down, so they keep accumulating.
- The sequence must go from producers → primary consumers → secondary consumers → tertiary consumers, as concentration increases with each level.
- Don't just state the order — always link it to "each organism consumes many of the organisms below it," which is what drives magnification.