Cellular respiration is a metabolic process that uses oxygen to break down glucose and produce energy in the form of ATP (adenosine triphosphate). The overall equation for cellular respiration is:
$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy (as ATP)$$
Fermentation is a metabolic process that does not use oxygen to break down glucose and produce energy. Instead, fermentation uses an organic molecule (such as NAD+) as an electron acceptor to break down glucose and produce energy in the form of ATP. The overall equation for fermentation is:
$$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + energy (as ATP)$$
Therefore, cellular respiration requires oxygen, whereas fermentation does not.
