Trophic level — Science definition
Defined in 2 courses:
- A feeding step in an ecosystem — producers, then primary consumers, then secondary consumers, and so on. (Life Science: Biology)
- A feeding position in a food chain — producers, then primary consumers, secondary consumers, and so on up to top predators. (Physics & Environmental Science)
Where it is taught
- Energy Flow in Ecosystems — Ecosystems & Conservation Decisions, Life Science: Biology, Grade 10
- Ecosystem Structure & Energy Flow — Ecology, Populations & Biodiversity, Physics & Environmental Science, Grade 12
Questions using trophic level
Problem 1
Which trophic level in an energy pyramid has the LEAST usable energy available?
- Producers
- Primary consumers
- Secondary consumers
- Top predators
Answer and explanation
Top predators
Energy is lost at every step, so the top predators at the peak have the least energy available.
Problem 2
Most of the energy at one trophic level does not reach the next because it is
- converted into matter
- used in respiration and released as heat, or not consumed
- stored permanently
- returned to the sun
Answer and explanation
used in respiration and released as heat, or not consumed
Organisms respire most of the energy they obtain, releasing it as heat, and a further portion of each level is never eaten.
Problem 3
Using a 10 percent transfer, how much of a producer level's 20,000 kJ reaches the second trophic level?
Answer and explanation
2000 kJ
20,000 × 0.10 = 2,000 kJ, the rest being respired, lost as heat, or not consumed.
Problem 4
Using a 10 percent transfer at each step, how much of a producer level's 20,000 kJ reaches the fourth trophic level?
Answer and explanation
20 kJ
20,000 × 0.1³ = 20 kJ. Three transfers reduce the available energy a thousandfold.
Taught alongside
- autotroph
- heterotroph
- biomass
- energy pyramid
- ten percent rule
- standing biomass
- transfer efficiency
- gross primary productivity (GPP)
- net primary productivity (NPP)
- ecological efficiency (10% rule)