Energy Transfers (WJEC GCSE Biology: Combined Science)

• Not all of the energy available at each stage of a food chain is transferred to the next trophic level
  • Only around 10% of the chemical energy consumed at each trophic level is passed on to the next
• It can be said that energy is lost from the food chain at each stage

Energy transfer in food chains diagram

Not all of the energy at each trophic level of a food chain is passed on to the next level

• Energy is lost from food chains because only the energy stored in biomass will be passed to the next trophic level; energy used for other processes, or transferred to the environment, is not available to consumers
• Energy may be used for:
  • Repairing damaged cells
  • Cell maintenance and growth
• Energy may be transferred to the environment in the form of:
  • Heat generated during cellular respiration
  • Waste materials, e.g. faeces and urine
• Energy losses from food chains explain why food chains are usually relatively short; the energy available at higher trophic levels eventually becomes too small

Energy losses from food chains diagram

Only energy that is converted into new biomass will be passed on to consumers in a food chain; energy that is used in cellular processes or lost as heat or in waste will not be available to higher trophic levels

Note that you do not need to know the term 'net production'

Higher Tier Only

• Percentage calculations can be used to calculate the efficiency of energy transfer at each stage of a food chain:

• • Remember that when calculating a percentage you divide a part by the whole; here the 'part' is the energy remaining for the next level, while the 'whole' is the energy received from the previous level

How does energy affect the number of organisms at each trophic level?

• The low efficiency of energy transfer at each trophic level means that there is less energy available to support organisms at higher trophic levels of a food chain
• This means that fewer organisms are present at higher trophic levels than at lower levels, i.e. there are more producers than top predators in a food chain
  • There are some exceptions to this, e.g. a tree is a single individual but can support many consumers