Aerobic respiration is ultimately the reaction of glucose with oxygen to generate carbon dioxide, water, and energy. However, in a cell this process involves the transfer of electrons from glucose to carriers such as NAD over a lengthy series of steps. Why don't cells employ the direct reaction of glucose with oxygen to generate energy?

Cells don't employ the direct reaction of glucose with oxygen to generate energy because the direct transfer of electrons from glucose to oxygen occurs via a combustion reaction that is incompatible with life.

Explanation:

Aerobic respiration is a process by which chemical energy is released in cells during the breakdown of food e. g glucose.

Cells don't employ the direct reaction of glucose with oxygen to generate energy because the direct transfer of electrons from glucose to oxygen occurs via a combustion reaction that is incompatible with life.

NAD is used to temporarily store high energy electrons harvested from glucose molecules in a series of gradual steps in the cytoplasm.

Glucose is a very high energy rich stable compound. Therefore to extract the energy it contains it must first be broken down in a step wise reactions called Glycolysis to generate ATPs needed in subsequent steps.

If glucose molecules reacted directly with oxygen (burnt in oxygen). This is an example of combustion reaction, which involves the transfer of electrons between glucose and oxygen atoms through pathways in which the energy produced can not be harness by the cells. it is therefore not physiologically compatible with normal cellular reactions of life.