Green plants are the primary producers, which produce energy by using solar energy. Green plants hold solar energy as chemical energy from where it flows as energy or chemical compounds to the herbivorous animals and from the herbivorous animals to carnivorous animal Energy is spent in every step on the way to flow from the producer to the carnivorous animals. Ecosystems maintain themselves by cycling energy and nutrients obtained from external sources. At the first trophic level, primary producers (plants, algae, and some bacteria) use solar energy to produce organic plant material through photosynthesis.
Almost all the energy is spent at the time of transfer of energy to the decomposers- from producers, herbivorous and carnivorous animals. This causes no energy to be transferred at the time of nutrient flow to inorganic nutrient storage. Inorganic nutrient materials are again transferred to producers from the nutrient storage. From this, it is understood that in eco-system the nutrient flows in a cyclic order with the eco-system. The energy flow is, however, one way and not cyclic.