TCE Biology — background
Ecosystem Energy Flow — Flashcards & Quiz
Ecosystem energy flow describes how energy captured from sunlight by producers passes to consumers, with much of it lost as heat at each transfer. Ecology is not part of the current TASC Biology Level 3 course, which covers science inquiry skills, regulation of cells and systems, and continuity and change. Treat this page as background: it builds understanding of how energy is transformed and transferred in photosynthesis and cellular respiration, which are part of the course.
Key Points
- Producers (plants, algae) capture light energy in photosynthesis and store it as chemical energy in organic compounds; they form the base of every food chain.
- Primary consumers eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers.
- Only about 10% of the energy at one trophic level (the range is roughly 5–20%) becomes biomass at the next. Most is released as heat by cellular respiration or lost in faeces and uneaten parts.
- Pyramids of energy always narrow toward the top, which limits most food chains to four or five levels.
- Energy flows one way through an ecosystem and must be resupplied by the sun; matter such as carbon and nitrogen is recycled by decomposers.
- Food webs are more realistic than food chains because most organisms eat, and are eaten by, several species.
Common Mistakes to Avoid
- Confusing energy flow (one-way, lost as heat) with nutrient cycling (matter is recycled).
- Drawing energy pyramids that widen toward the top — pyramids of energy always narrow, although pyramids of numbers can be inverted.
- Treating the 10% figure as exact — it is an approximate average.
- Saying energy is "used up" — it is converted to heat, which cannot be passed on to the next trophic level.
- Forgetting that cellular respiration is the main reason energy is lost between levels.
Exam Strategy
Energy flow is background for the TASC course rather than assessed content. Use it to strengthen your answers on photosynthesis and respiration: photosynthesis converts light energy into the chemical energy of glucose, and cellular respiration releases that energy as ATP and heat. When you explain the respiration equation, you can link the heat released to why only a small fraction of energy passes from one organism to the next.
Sample Flashcards
Q1: What role do producers play in ecosystem energy flow?
Producers such as plants and algae are autotrophs. In photosynthesis they absorb light energy and use it to convert carbon dioxide and water into glucose, storing the energy as chemical energy in organic compounds. All other organisms in the ecosystem depend directly or indirectly on this stored energy, so producers form the first trophic level of every food chain.
Q2: What are trophic levels?
Trophic levels are the feeding positions in a food chain. Producers are the first level, primary consumers (herbivores) the second, secondary consumers (carnivores that eat herbivores) the third and tertiary consumers the fourth. An omnivore can feed at more than one level. Decomposers break down dead material from every level and return nutrients, but not energy, to producers.
Q3: Why is only about 10% of energy passed from one trophic level to the next?
Most energy taken in by an organism is not stored as new biomass. Much is released as heat during cellular respiration to power movement, growth and maintaining body temperature. Some is lost in faeces, urine and parts that are not eaten, such as bones and roots. On average only about 10% (roughly 5–20%) becomes biomass available to the next level.
Q4: Why do pyramids of energy always narrow toward the top?
A pyramid of energy shows the energy available at each trophic level per unit area per year. Because energy is lost as heat at every transfer, each level must hold less energy than the one below it, so the pyramid always narrows. This also limits food chains to about four or five levels, since too little energy remains to support further consumers.
Q5: How does energy flow differ from nutrient cycling?
Energy flows one way: it enters as sunlight, passes through trophic levels and leaves as heat, which cannot be reused by organisms. It must be continually resupplied by the sun. Nutrients such as carbon, nitrogen and phosphorus are matter, so they are recycled: decomposers break down dead organisms and wastes, returning these elements to the soil, water and air for producers to reuse.
Revision Tip
Trophic-level calculations are quick to drill — build a Revizi deck of short food-chain problems, then link each to the photosynthesis and respiration equations you need for the course.
Related Concepts
Last updated: 9 October 2026 · 6 sample flashcards