The total production of organic compounds by plants is referred to as primary productivity or production. This represents the total amount of light energy transformed into chemical energy through photosynthesis. Only about 1 – 5 % of the solar energy in any given location actually is captured for use or storage by plants. After the metabolic requirements of producers (plants or other photosynthetic organisms) are met, the total energy (accumulated as biomass) available to be passed through the food chain is called net primary productivity.

Primary production in an ecosystem predominately occurs through the photosynthetic action of autotrophs (producers) such as plants, algae, and some bacteria. Once this energy has been captured by autotrophic organisms, it is passed on to heterotrophs (consumers) in different trophic levels.

A trophic level is made of all the organisms that share the same number of energy transfers from sunlight energy (plants are the first, herbivores the second, and carnivores the third). Transfer of energy between trophic levels is inefficient because much of the energy captured is lost to building and maintaining the bodies of organisms. Less than 10% of the energy obtained by organisms at each level is available to organisms in the next trophic level. The efficiencies of different trophic levels can be illustrated in ecological pyramids, either as available energy, biomass or numbers of organisms.

The total dry weight of organisms (standing crop) in a particular trophic level is referenced as biomass. Most pyramids follow the typical pattern of narrowing at each level, however in some aquatic ecosystems, the pyramid may be inverted. In the example, phytoplankton grow and reproduce so rapidly that they can support a large population of zooplankton even though at any one time, the biomass of phytoplankton is smaller than that of the zooplankton.