Biomass is living or recently dead tissues. 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.
The amount of biomass can be measured 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 → sparrowhawk
So in an ecosystem the clover has more biomass than all the snails, which have more biomass than all the thrushes and so on. Pyramids of biomass are always perfectly shaped. 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: