Organisation in ecosystems - OCR Gateway Pyramids of biomass

Biomass

Biomass is tissue from living organisms. The mass of your body is biomass because you are alive. Wood is considered biomass because it was recently a plant. Fossil fuels are not considered biomass because they are the remains of organisms that died millions of years ago and have been chemically changed from the original living tissue.

Pyramids of biomass

We can measure the amount of biomass at different trophic levels in a food chain. The total biomass of each trophic level is often represented as a modified bar chart called a pyramid of biomass. In a food chain from a healthy ecosystem the biomass at each trophic level must reduce. An example of a food chain is:

clover → snail → thrush → sparrowhawks

So in an ecosystem all of the clovers have more biomass than all of the snails, which have more biomass than all of the thrushes and so on. Pyramids of biomass should always be perfectly shaped as a pyramid. If this is not the case, then the ecosystem is likely to be unhealthy and in danger.

Pyramids of biomass must be drawn with the:

1. bars equally spaced around the midpoint
2. bars touching
3. bar for the producer at the bottom
4. length of each bar proportional to the amount of biomass available at each trophic level