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. It was through evolution that plants, herbivores, and carnivores came about and developed ecological associations between each other.