Energy flow

Energy flow

(a) Energy does not cycle through ecosystems but instead enters ecosystems and is used

up within ecosystems. Ultimately, energy is lost from ecosystems primarily as waste

heat, the most thermodynamically unavailable form of energy.

(b) “Energy enters most ecosystems in the form of sunlight. It is then converted to

chemical energy by autotrophic organisms, passed to heterotrophs in the organic

compounds of food, and dissipated in the form of heat . . . The movements of energy

and matter through ecosystems are related because both occur by the transfer of

substances through feeding relationships. 

However, because energy, unlike matter,cannot be recycled, an ecosystem must be powered by a continuous influx of new energy from an external source (the sun). Thus, energy flows through ecosystems, while matter cycles within them.”

 (c) Note that energy flows through ecosystems mostly as bonds between carbon atoms

and bonds between carbon and hydrogen atoms, e.g., as one finds in carbohydrates

and lipids; consequently, within and between organisms the carbon cycle and the flow

of energy are quite similar, at least until the two are decoupled in the course of

cellular respiration (i.e., the separation of carbon atoms from their energy).