GED Science TestLife ScienceHard
An ecologist is studying the energy flow in a forest ecosystem. She measures the total biomass at different trophic levels. If the primary producers (plants) have 10,000 kcal of energy, and assuming typical energy transfer efficiency, how much energy would typically be available to tertiary consumers?
- A100 kcal
- B1 kcal
- C0.1 kcal
- D10 kcal
Show answer & explanationAnswer & explanation
Correct answer: D. 10 kcal
According to the 'Ten Percent Rule' in ecology, only about 10% of the energy from one trophic level is transferred to the next. Primary producers (10,000 kcal) -> Primary consumers (10% of 10,000 = 1,000 kcal) -> Secondary consumers (10% of 1,000 = 100 kcal) -> Tertiary consumers (10% of 100 = 10 kcal).
Why the other options are wrong
- A. 100 kcal would be available to secondary consumers, not tertiary.
- B. 1 kcal would be available to quaternary consumers (if present).
- C. 0.1 kcal would be available to quinary consumers (if present).
Ten Percent Rule (Ecology)
A principle in ecology stating that only about 10% of the energy from one trophic level is transferred to the next trophic level; the rest is lost as heat.
- Energy transfer is inefficient
- 90% energy loss at each transfer
- Limits the number of trophic levels in an ecosystem
Memory trick: Energy pyramid: lose a zero each step up