A community of organisms interacting with abiotic component in a particular region/area will be called as ecosystem. The living and non-living components are linked together by the nutrient cycles and energy flow through each trophic level.
In a typical food chain, the energy that is transferred from one trophic level to the next is always unidirectional and never forms a cyclical pattern. The main source of energy is the sun (solar energy), which is used by producers to make food, and then it is consumed by consumers and so forth.
Of the total solar energy available to us, only 1-5% is utilized by the producers for making food. The energy available to every organism in each trophic level is only 10% for the successive trophic level. Also, the energy requirement in each successive trophic level increases for maintenance of body.