Re: What is Cellular Respiration and what does it do for us?

Used in this context, the term "respiration" refers to the biochemical 
process through which the cell generates energy by oxidizing fuel.  The 
major form of energy that a cell can use is ATP (i.e., adenosine 
triphosphate).  The fuels that most cells can use include things like 
sugars (i.e., glucose), fats (fatty acids), and the building blocks of 
proteins (i.e., amino acids).  The reason this process of generating 
chemical energy for the cell is called "oxidation" is because it usually 
requires molecular oxygen (i.e., O2) for it to happen.  The end products of 
cellular respiration are carbon dioxide, water and of course energy in the 
form of ATP.  This process occurs in a specialized compartment or organelle 
within the cell called mitochondria.  Often times mitochrondia are refered 
to as the "power plants" of the cell for this reason.  So in summary, 
cellular respiration is a process that occurs within the mitochondria of 
cells whereby some of the components of food (fats, sugars, and proteins) 
are chemically broken down in a controlled, highly-regulated manner to make 
ATP, chemical energy.  The cell needs oxygen for this process to work 
properly and it excretes carbon dioxide as waste products.  We breathe or 
respire (another but different use of the term) in order to remove the 
carbon dioxide from our body and replenish the oxygen that our cells need.  
To answer the second part of your question, "What does it do for us?"  The 
short answer is life!  Of course, you know that without oxygen, we would 
die very quickly.  The reason is because cellular respiration would stop.  
The more complicated answer might require a fuller understanding of what 
the cell uses ATP for.  In short, it uses ATP to do work.  To make things 
(e.g., proteins, hormones, membranes), to divide, to live.