Different components for a universal model of energy flow are :

A generalised energy flow model of ecosystem—Boxes represent biotic components and the arrows show the pathways of energy transfer

When a herbivore eats a plant, then it digests and oxidizes the ingested food to liberate energy which is equal to that used in synthesizing the organic biomass by the plant. Some of the released energy is lost as heat while only a part of energy is used in building the biomass of the herbivore, called gross secondary productivity. The same is repeated when the herbivore is eaten by a primary carnivore and so on. At each transfer, about 80-90% of potential energy is dissipated as heat while only 10-20% of energy is available to next trophic level. Thus, there is a decline in the amount of energy passing from one trophic level to the next trophic level. The study of energy transfer was called bioenergetics.

Secondary productivity tends to be about 10 per cent at the herbivore level, although efficiency may be higher, as 20 per cent at the carnivore level.

So regarding the energy flow, an ecosystem is characterized by :

1. Unidirectional flow of energy.

2. Decrease in useful energy.

3. Return of radiant energy of sun to non-living system as heat.