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AQA GCSE · Question 07.4 · Ecology
Chickens can use 80% of the biomass from the maize seeds they eat for respiration and growth. What happens to the remaining 20% of the biomass in the maize seeds?
Chickens can use 80% of the biomass from the maize seeds they eat for respiration and growth. What happens to the remaining 20% of the biomass in the maize seeds?
How to approach this question
Think about the transfer of energy and biomass in a food chain. Not all of the food an animal eats is converted into its own body mass. Where does the rest of it go?
Full Answer
It is lost as waste, for example in faeces/urine (egestion/excretion).
When an organism consumes food, not all of the biomass is transferred to the consumer's own biomass. Energy and mass are lost at each trophic level. The 80% mentioned is used for life processes (respiration) or converted into the chicken's own body mass (growth). The remaining 20% represents the portion of the maize that is not digested and absorbed by the chickens. This undigested material is passed out of the body as waste products, primarily faeces (egestion). Some biomass is also lost through excretion of metabolic waste products like urea in urine.
Common mistakes
✗ Saying it is "lost as heat" - this is a loss of energy from respiration, which is part of the 80%, not the remaining 20% of biomass.
✗ Saying it "decomposes" - this happens after it becomes waste, it doesn't explain what happens inside the chicken.
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