The second process involves the movement of energy, in the form of organic molecules, from plants to herbivores, and then finally to carnivores through biomass consumption. There are functional as well as structural relationships between the units of a system. The structure within the food chain is defined by the functional relationships between the elements and attributes of the system. Function implies the flow and transfer of some material . Systems exchange energy and matter internally and with their surrounding environment through various processes of input and output .
Herbivores consume the constructed plant organic molecules for nutrition to run their metabolism.
The herbivores then provide food for the carnivores . Function requires the presence of some driving force , or some source of energy. The driving force in the food chain is the sun. All systems show some degree of integration . Integration in the food chain comes primarily from the process of evolution.