Re: What is the importance of oxygen in respiration?

Most of the oxygen that is used in respiration is to obtain chemical energy 
from the fats and carbohydrates in our food. These fats and sugars are 
essentially burned in a controlled way (being oxidized to water and 
carbon dioxide). The energy is trapped in the form of ATP that is used by 
our bodies to synthesize proteins, move muscles etc. 
Breakdown of food by glycolysis, fatty acid oxidation and the citric acid 
cycle result in the formation of NADH and FADH2. These are energy-rich 
molecules because they contain a pair of electrons that have a high 
transfer potential. When these electrons are transferred to oxygen (to make 
water) a large amount of energy is liberated. This process is called 
oxidative phosphorylation. These reactions are performed by a series of 
electron carrier proteins (the respiratory chain) in the mitochondria. As 
elecron pass down the respiratory chain, protons are moved from one side of 
the mitochondrial membrane to the other. This results in an electrical 
potential across the membrane that ultimately provides the energy to make 
ATP. (The ATP is made by another complex of proteins in the membrane called 
the F1 ATPase). The last electron carrier in the respiratory chain is 
called cytochrome oxidase. It contains heme and copper ions that add 4 
electrons and 4 protons to an oxygen molecule to produce 2 molecules of 
water.
Although most of the oxygen is used in this way, a small amount is also 
needed for the synthesis and breakdown of other metabolically important 
molecules (such as steroid hormones).