A question about the Cylons...

Spoilers for those even more behind than me!

I just watch season 3 episode 6 where they discover ye olde virus that can destroy Cylons because of their lack of antibodies... Now, what I want to know is, and this may be explored further down the line, but what is the ratio of human to robot? I ask because Helo stops the Cylon genocide by suffocating the Cylon prisoners and taking all the air out of their cell... BUT if they're robots, why do they even need air?

Answers?

For the uninitiated I bet this post is a bit like when I was 14 and phoned my friend Nim for help getting through the RPG game Day of the Tentacle and his mum had to listen to things like, get the broom head and put it on your head like you're a woman, now flush the tin can down the toilet so it can become a time generator...