Energy flow:- Ultimate source of energy in an ecosystem is sunlight or sun, while ultimate source of food in an ecosystem is producer.

• Energy flow in an ecosystem is unidirectional or non-cyclic.

Energy flow follow both (1) & (2) law of thermodynamics.

It is applicable both for energy and food. During transfer of energy 1 food from one tropic level to another trophic level. Only 10% remain conserved, rest 90% loss in the form of heat.

• Grass    →          Deer      →          Tiger

           1000 kg               100 kg                 10 kg