Pyramids of Biomass

Below is an energy pyramid that shows the flow of energy, from one trophic level to another.

  • The trophic level is the position of an organism in a food chain or web

As energy moves up through the trophic levels in a food chain, most of it is lost. If there are 1000 joules of energy in a primary producer (e.g. grass), then only around 100 joules of energy will be passed onto the next trophic level. In food chains, we represent the flow of energy by using arrows.

The diagram below shows a pyramid of biomass for the food chain: Clover → Grasshopper → Snake → Fox. It shows the biomass at each trophic level in the food chain.

  • Biomass refers to the total mass of organisms in a given area or volume.

As you go up the pyramid, the bars get smaller. This means that the total mass of the organisms on each level is decreasing. Although an individual snake might weigh more than a grasshopper, the combined mass of all grasshoppers is greater than that of all snakes.

Producers (e.g. plants and algae) only use around 1% of the light energy that reaches them for photosynthesis. At each trophic level, as one organism consumes another, most of the biomass is either lost or used.

Only around 10% of the biomass will be transferred up to the next trophic level. So, the tertiary consumer will have around 0.1% of the biomass of the producer in the food chain.

Most Biomass is Not Transferred

There are three reasons that most of the biomass is not transferred:

  • Organisms don’t typically consume every part of their prey.
  • Organisms cannot digest every part of what they consume. The parts that cannot be broken down are excreted as faeces.
  • A significant amount of the absorbed biomass is used for respiration, releasing energy. The excess becomes waste products, like carbon dioxide and urea. This means that only a small portion of the biomass is available to be transferred to the next trophic level.

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