Transfer of biomass

Ecology · Trophic levels in an ecosystem · note 3 of 3

Spec 4.7.4.3

Triple only

Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean

Download all Trophic levels in an ecosystem notes (PDF)Download all notes (PDF)4 pages

Transfer of biomassSpec 4.7.4.3

In short

Only approximately 10% of the biomass at each trophic level is transferred to the level above. Biomass is lost because some ingested material is egested as faeces, some absorbed material is lost as waste such as carbon dioxide, water and urea, and large amounts of glucose are used in respiration. So fewer organisms can be supported at higher levels.

Producers are mostly plants and algae which transfer about 1% of the incident energy from light for photosynthesis.

Only approximately 10% of the biomass from each trophic level is transferred to the level above it.

How biomass is lost

Not all the ingested material is absorbed. Some is egested as faeces.
Some absorbed material is lost as waste, such as carbon dioxide and water in respiration, and water and urea in urine.
Large amounts of glucose are used in respiration.

Efficiency of biomass transfer

efficiency (%) = biomass transferred to the next level ÷ biomass available at the previous level × 100

Efficiency of transfer

Caterpillars eat 250 g of leaves and their body mass increases by 20 g. Calculate the efficiency of biomass transfer.

Biomass transferred = 20 g.
Biomass available = 250 g.
Efficiency = 20 ÷ 250 × 100 = 8%.

Answer: 8%

Maths skill:

You can also be asked for efficiency as a fraction. 20 ÷ 250 simplifies to 2/25. Check which one the question asks for.

Effect on numbers of organisms

Because so much biomass is lost at each step, less biomass is available to each higher trophic level. This means fewer organisms can be supported at each higher trophic level, and food chains have only a few trophic levels.

Common mistake:

Do not just say biomass is 'used up'. Name the losses: egested as faeces, lost as carbon dioxide and water in respiration, and as water and urea in urine.

Quick check

What is trophic level 1, and what are those organisms called?
Show answer
Plants and algae, called producers.
What is an apex predator?
Show answer
A carnivore with no predators.
How do decomposers break down dead material?
Show answer
They secrete enzymes into the environment and small soluble food molecules diffuse in.
Approximately what percentage of biomass passes to the next trophic level?
Show answer
About 10%.
Give two ways biomass is lost between trophic levels.
Show answer
Egested as faeces; lost as carbon dioxide and water in respiration, and as water and urea in urine.

Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026

Frequently asked questions

Why is energy lost between trophic levels?

Energy is lost between trophic levels because biomass is lost: only about 10% of the biomass passes to the next level. Some ingested material is egested as faeces. Some absorbed material is lost as waste, such as carbon dioxide and water from respiration and water and urea in urine. Large amounts of glucose are also used in respiration.

What is a pyramid of biomass?

A pyramid of biomass is a diagram that shows the relative amount of biomass at each trophic level of a food chain, with the producers at the bottom. Each bar is narrower than the one below, because biomass decreases at each higher trophic level. The length of each bar is drawn to scale, proportional to the biomass of that level.

Why are food chains short?

Food chains are short because so much biomass is lost at each step. Only about 10% of the biomass at one trophic level is transferred to the level above, as the rest is egested, lost as waste or used in respiration. So less biomass is available at each higher level, and fewer organisms can be supported.

All 4 questions on Trophic levels in an ecosystem

Finished trophic levels in an ecosystem? Test yourself:Exam questions Flashcards