Energy is transferred in an ecosystem. Autotrophs make their own food, heterotrophs cannot so eat to gain energy. Primary consumers (herbivores) eat plants (autotrophs). Secondary consumers (carnivores) eat secondary consumers and are sometimes the top predator. Some animals eat plants and organisms (omnivores). Decomposers feed on dead material.

Feeding relationships are shown in food chains and food webs. The position a species occupies in a food chain is its trophic level.

Energy transfer is measured in GPP (Gross Primary Productivity) which is the rate at which energy is incorporated into organic molecules. GPP = GPP/light energy x 100.

NPP (Net Primary Productivity) is the rate that organic molecules are made into new biomass. NPP = GPP – R

% efficiency of energy transfer between trophic levels = (NPP of a level/NPP of previous level) x 100

Energy transfer is not efficient:

  • Not all of the available food gets eaten or is indigestible/inedible
  • Some energy is lost in waste
  • Energy is used in respiration for movement and chemical reactions and is lost to the environment as heat
  • Some sunlight can’t be used because it hits parts of the plant that cannot photosynthesise

As you go up trophic levels, the transfer of energy gets less.