The diagram below shows the energy flow in the ecosystem.
The producers (photo-synthetic plants) synthesize organic substances by the process of photosynthesis. The chemical energy so stored in plants is called gross primary production. The producers themselves first use the synthesized organic substances in the process of respiration in which some energy is used in oxidation of organic substances. The rest of the energy, called the net primary production, is stored for the growth, development and important metabolic processes.
Next the primary consumers (herbivores) obtain their food from the producers, so they obtain only a small part of energy from the producers and the rest is wasted in decay of producers. A small part of the energy obtained by the primary consumers is utilized in respiration and the remaining part is stored in them as food.
Afterwards, a small part of the energy stored as food in the primary consumers is obtained by the secondary consumers (carnivores). They again make use of a part of the energy in respiration and rest is stored in them as food.
By repeating the sequence, the tertiary consumers (carnivores) obtain energy as food from the secondary consumers and utilise a small part of it in respiration and remaining energy is wasted in their decay and decomposition.
The energy flow in ecosystems is thus linear i.e., it moves in a fixed direction. At the end, the energy reaches to the degraded (or unuseful) state. It does not return to the sun to make the process cyclic.
