Respiration is another life process. Like other living organisms, a tree must respire. The process of respiration consists of oxidizing (burning at low temperature) dextrose sugar; although some energy is lost as heat, most of the energy released during the process is used by the organism for its vital processes. Thus sugar is a source of energy for a tree just as it is for a football player. The chemical reaction of respiration is a reversal of the chemical reaction of photosynthesis, as seen from the following scheme:

PHOTOSYNTHESIS : Carbon dioxide + water + energy expended—dextrose + oxygen;

RESPIRATION : Dextrose + oxygen—> carbon dioxide+water+energy released.

In daytime both photosynthesis and respiration occur at the same time in trees.