Energy transfer

Energy is transferred along food chains from one trophic level to the next. However, the amount of available energy decreases from one trophic level to the next.

Lowest (fourth) tier of pyramid of biomass showing the producers, for example oak tree, flowers. They produce 25 MJ per meter squared per year.

Energy transfer

A pyramid of biomass

Energy loss

In a food chain only around 10 per cent of the energy is passed on to the next trophic level. The rest of the energy passes out of the food chain in a number of ways:

  • it is used as heat energy
  • it is used for life processes (eg movement)
  • faeces and remains are passed to decomposers

Less energy is transferred at each level of the food chain so the biomass gets smaller. As a result, there are usually fewer than five trophic levels in food chains.

Percentage efficiency of energy transfer

The percentage efficiency of energy transfer between trophic levels can be calculated using the equation:

curriculum-key-fact
energy transferred to next level ÷ total energy in × 100

Worked example

Energy flow from producers to primary consumers is 500 kj, primary to secondary is 75 kj, secondary to tertiary is 7.5 kj.  Producers lose 4500 kf, primary lose 425 kj and secondary lose 67.5 kj

Work out the percentage efficiency of energy transfer between producers and primary consumers in the example.

Question

Calculate the total energy that came into the level of the food chain.

4500 kJ + 500 kJ = 5000 kJ

Question

Identify how much energy is transferred to the next level.

500 kJ

Question

Calculate the efficiency of this transfer using the equation.

energy transferred to next level ÷ total energy in × 100

500 kJ ÷ 5000 kJ × 100 = 10%

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