Re: Why do our bodies actually need oxygen?

Hello Adrienne!  Your question is a very good one, it gets right down to 
the point!  Of course, the answer is a bit complex, but I suspect that 
you will pick up on it quickly.  So hold on tight!
In the cells of our body are lots of organelles (cell organs).  One of 
these is called mitochondria.  They are in every cell and are known as the
powerhouses of the cell.  Mitochondria take different elements and nutrients
from the cell (the cell gets them from your blood and your blood gets them from 
your food, which is why we eat) and sends them through a mitochondrial factory.  
This "assembly line" is called the Krebbs cycle.  At the end of this assembly 
line, you can find the most basic source of (animal) energy.  It's called ATP 
(this is a short name for Adeninetriphosphate).  So here we are, with a bunch 
of ATP.  Now what?  Well, you need to burn it and get all the energy out of it!
In order to do that, guess what we need (this is where you scream "OXYGEN!!")
Yep, just like burning a piece of wood, any type of burning takes oxygen.  So 
we breathe.  We make a lot of ATP (I don't know exactly how much, but to 
give you an idea, it's like millions per second. A lot), so we need to get a lot of 
oxygen in there to get the energy from our little ATP's.  And there you go.
Interestingly enough, I answered a question about how cyanide works a month
or two ago.  If you want to see how important oxygen is, look up that question
under "how does cyanide work?".  It'll show you just how important oxygen is.
Thanks for your question!    
Cheers!
Jen Paur