Q1. [3] medium thorough-understanding
A food chain in a grassland ecosystem is: Grass → Grasshopper → Frog → Snake → Hawk. If the grass captures 10,000 J of energy from sunlight, how much energy (in joules) is available to the snake? Show your reasoning.
Generated by claude-sonnet-4-6 · 2026-06-26 00:59 · grounding rag
Model Answer
Food chain: Grass (T1) → Grasshopper (T2) → Frog (T3) → Snake (T4) → Hawk (T5)
10% Law: Only 10% of energy passes from one trophic level to the next.
Calculation:
- Grass (T1): 10,000 J
- Grasshopper (T2): 10% of 10,000 = 1,000 J
- Frog (T3): 10% of 1,000 = 100 J
- Snake (T4): 10% of 100 = 10 J
Energy available to the snake = 10 J
Source: Chapter 13, Food Chains and Webs (Section 13.1.1)
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Explanation
- The 10% law states that only 10% of energy at one trophic level is transferred to the next; the rest is lost as heat, digestion, etc.
- Snake is at the 4th trophic level, so apply the 10% rule three times: 10,000 → 1,000 → 100 → 10 J.
- Examiners expect you to show each step clearly — don't just state the final answer.
- A common mistake is starting the calculation from the wrong organism; always identify trophic levels first.