What is aerobic respiration and why is it important in the human body?

Aerobic respiration is the process by which energy is released from glucose in the presence of oxygen (as indicated by the word 'aerobic'). While in reality it is a complex, multi-step series of reactions controlled by enzymes (so called "biological catalysts") it can be summarised in the following equation: glucose + oxygen --> carbon dioxide + water (+ energy) This process is occurring in the cells of your body right now - more specifically in the mitochondria. The mitochondria are organelles sometimes referred to as the 'power house' of the cell and, as you might expect, the number of mitochondria found inside a cell is proportional to the energy demands of the tissue that the cell is part of. Almost all cells have mitochondria (a notable exception being Red Blood Cells) to provide them with the energy that they need to carry out basic cellular functions such as protein production and active transport (the movement of a substance against its concentration gradient using energy). However in tissues with high metabolic activity such as the liver there needs to be more to keep up with all of the demands of the cell. If there is too little Oxygen present, anaerobic respiration might occur. This is a less efficient method of energy release than aerobic respiration because oxygen is involved in a key, energy releasing step in the process of respiration. When this step cannot occur (such as when there is limited oxygen) an alternate pathway is taken which leads to a small amount of energy being released along with (in the case of humans and non-human animals) lactic acid.