Energy flow and nutrient cycles

Energy can neither be created nor destroyed, but can be changed from one form to another.

Energy enters the biosphere as light (solar radiation) and leaves as heat (terrestrial radiation).

Thus energy flows in one direction through all ecosystems; living organisms exploit light energy by changing it to other forms.

Matter such as carbon and nitrogen are nutrients; the earth has a finite amount of these, and they cycle through organisms and abiotic components of ecosystems.