Transfers Along a Food Chain (Edexcel IGCSE Biology)

Revision Note

Transfer of Energy

  • Light energy from the sun enters the first trophic level of food chains when producers convert light energy into chemical energy

    • Light energy is transferred to chemical energy in the form of carbon-containing compounds within the biomass of producers

  • Energy and chemical substances are then transferred through food chains when:

    • primary consumers eat producers, breaking down the carbon compounds within their biomass and using the energy and substances released to build new biomass within their own tissues

    • secondary consumers eat primary consumers, again breaking down the molecules that make up their biomass and using the energy and substances to build their own tissues

    • this process is repeated at each trophic level

  • Some energy and substances are lost to the environment between trophic levels

Energy is transferred from the sun, to grass, into primary consumers and then into secondary consumers in a food chain

Energy and chemical substance are transferred through food chains when organisms consume other organisms

Energy Loss Between Trophic Levels

  • When organisms consume other organisms, not all of the stored energy is passed to the next trophic level; only around 10% of the energy available at each trophic level is converted into biomass at the next level

    • This explains why food chains are short; the energy available eventually becomes too small to support another trophic level

Energy losses take place between each trophic level of a food chain

Energy is lost at each trophic level of a food chain

Explaining energy loss from food chains

  • Energy may be lost from food chains because consumers are not able to digest and absorb all of the chemical energy stored in food organisms

    • Organisms rarely eat every part of the organism they are consuming, e.g. many predators do not consume the bones, fur, teeth or claws of their prey, so energy stored in uneaten body parts does not pass to the consumer

    • Not all the ingested material is digested and absorbed, some is egested as faeces, e.g. plant material can be difficult to digest and passes through the digestive system of herbivores

  • Once a consumer has digested and absorbed its food, not all of the energy will be converted to biomass; energy may be unavailable for building biomass due to:

    • heat loss during respiration

    • transfer into waste products, e.g.

      • carbon dioxide and water are waste products of respiration

      • urea is a waste product of protein breakdown

Energy Losses from a herbivore due to respiration, egestion and excretion

Energy may be unavailable to the next trophic level when it is lost as heat during respiration, when undigested food is egested, and when energy is transferred to waste products

Calculating the efficiency of energy or biomass transfer

  • You may be asked to calculate the efficiency of energy and biomass transfers between trophic levels using percentages

Worked Example

The food chain below contains four trophic levels, and indicates the total biomass present at each level.

food chain containing 1450 kg clover, 138 kg snails, 14.1 kg thrushes and 1.18 kg sparrowhawks and

Calculate the efficiency of biomass transfer from the first to the second trophic level. Give your answer to 3 significant figures.

Use the equation:

percentage space efficiency space equals fraction numerator biomass space in space higher space trophic space level over denominator biomass space in space lower space trophic space level end fraction cross times 100

Answer

Step 1: determine the biomass of the first and second trophic levels

  • first trophic level = clover = 1450 kg

  • second trophic level = snails = 138 kg

Step 2: enter numbers into the equation

New WE - calculating-efficiency-of-biomass-transfers_2, downloadable IGCSE & GCSE Biology revision notes

Examiner Tips and Tricks

Note that energy and biomass are very closely related (energy is stored within the biomass of an organism); this means that:

  • efficiency of energy transfer can be calculated in exactly the same way as efficiency of biomass transfer

  • loss of energy results in loss of biomass at each trophic level

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.