TCE Biology — Level 3
Ecosystem Energy Flow — Flashcards & Quiz
Ecosystem energy flow describes how energy moves from the sun through producers to various consumer levels and is lost as heat at each transfer. TCE Biology Level 3 expects you to construct food chains and webs, calculate energy transfer efficiency between trophic levels, and explain why ecological pyramids narrow toward the top.
Key Points
- Producers (plants, algae) capture solar energy via photosynthesis; they form the base of the food chain.
- Primary consumers eat producers (herbivores); secondary consumers eat primary consumers (carnivores); tertiary consumers eat secondary.
- Energy transfer efficiency between trophic levels is typically ~10% — 90% is lost as heat, respiration, or undigested material.
- Energy pyramids always narrow toward the top because of the 10% rule. This limits food chain length (usually 4-5 levels max).
- Decomposers (bacteria, fungi) return nutrients to the soil by breaking down dead organisms — they are essential for nutrient cycling.
- Food webs are more realistic than chains because most organisms eat multiple food types.
Common Mistakes to Avoid
- Confusing energy flow (one-way, lost as heat) with nutrient cycling (recycled).
- Drawing energy pyramids that widen toward the top — they always narrow.
- Forgetting that only ~10% of energy is transferred between trophic levels.
- Treating decomposers as separate from the food chain — they are part of it, returning nutrients.
- Claiming all food chains have the same number of levels — energy loss limits length.
Exam Strategy
TASC Level 3 energy flow questions ask you to construct food chains, calculate energy at each level, or explain pyramid shape. Method: (1) identify producers, primary/secondary/tertiary consumers, (2) apply the 10% rule to calculate energy at each level, (3) draw the pyramid with labelled values, (4) explain the limit on food chain length.
Sample Flashcards
Q1: Explain why energy flow in an ecosystem is described as one-way and non-cyclical.
Energy enters ecosystems as sunlight, is converted to chemical energy by photosynthesis, and passes through trophic levels. At each level, most energy (~90%) is lost as heat through cellular respiration and is unavailable to higher levels. Energy cannot be recycled — it must be continuously supplied by the sun. This contrasts with nutrients, which are recycled.
Sample Quiz Questions
Q1: Energy in an ecosystem is recycled between trophic levels by decomposers.
Answer: FALSE
NUTRIENTS are recycled by decomposers, but ENERGY flows one way and is ultimately lost as heat. Energy cannot be recycled — it must be continuously supplied by the sun through photosynthesis.
Revision Tip
Trophic level calculations are drillable — build a Revizi deck with 5+ food chain scenarios and energy transfer calculations to lock in the 10% rule.
Last updated: March 2026 · 1 flashcards · 1 quiz questions