In the following food chain, if 50 J of energy was available to the hawk, how much energy would have been present at the first and third trophic levels ? Justify your answer.
Grass → Grasshopper → Frog → Snake → Hawk
Generated by claude-sonnet-4-6 · 2026-06-15 06:43 · grounding rag
Model Answer
Using the 10% law, energy transfers as follows (going backwards from hawk):
- Hawk (5th trophic level) = 50 J
- Snake (4th) = 500 J
- Frog (3rd trophic level) = 5,000 J
- Grasshopper (2nd) = 50,000 J
- Grass (1st trophic level) = 5,00,000 J (500,000 J)
1st trophic level (Grass) = 5,00,000 J; 3rd trophic level (Frog) = 5,000 J
Only 10% of energy passes to the next level; the rest is lost as heat, digestion, and work.
Source: Chapter 13, Section 13.1.1
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Explanation
- The 10% law states that only 10% of energy at one trophic level is available to the next. To find energy at lower levels, multiply by 10 for each step going backward.
- Hawk is the 5th trophic level in this chain, so go back 4 steps to reach Grass (1st) and 2 steps to reach Frog (3rd).
- Examiners expect you to show the calculation chain clearly and state the reason (10% law / energy loss as heat).