Biomass is the total mass of living material in a given area (or volume, for aquatic ecosystems) at a particular time.In any ecosystem, producers synthesise organic compounds from carbon dioxide in the atmosphere or dissolved in water. Most of the sugars they make are used as respiratory substrates, releasing energy for the plant's own processes. The rest are used to make other groups of biological molecules, such as cellulose, starch, lipids, proteins and nucleic acids. These molecules form the biomass of the plant. Consumers build their own biomass from the molecules in the food they eat.Biomass is a chemical energy store. When an organism is eaten, some of this chemical energy is transferred to the next trophic level.Biomass can be measured in two ways, in each case per given area or volume:• as the mass of carbon in the organisms, or
• as the dry mass of tissue (the mass with all water removed).Fresh (wet) mass is not used, because water content varies a lot, for example with the weather, and water is not part of the chemical energy store.Units are usually g m−2 for an area of land, or g m−3 for a volume of water. When a time is included, for example g m−2 yr−1, the value describes how fast biomass is produced.Example: 4 quadrats, each 0.25 m2, contain a total dry mass of grass of 300 g. The total area sampled is 1 m2, so the biomass is 300 g m−2.
• as the dry mass of tissue (the mass with all water removed).Fresh (wet) mass is not used, because water content varies a lot, for example with the weather, and water is not part of the chemical energy store.Units are usually g m−2 for an area of land, or g m−3 for a volume of water. When a time is included, for example g m−2 yr−1, the value describes how fast biomass is produced.Example: 4 quadrats, each 0.25 m2, contain a total dry mass of grass of 300 g. The total area sampled is 1 m2, so the biomass is 300 g m−2.