The human body carries out its main functions by consuming food and turning it into usable energy. Immediate energy is supplied to the body in the form of adenosine triphosphate (ATP). Since ATP is the primary source of energy for every body function, other stored energy is used to replenish ATP
Cellular respiration needs oxygen and produces carbon dioxide, whereas photosynthesis consumes carbon dioxide and produces oxygen. Free oxygen is required for cellular respiration by us and most other organisms