By itself, bio
is most often a modern abbreviation for "biographical sketch", and is pronounced "BY-oh". In my experience, it is not
usually used as a synonym for biography
(though Merriam-Webster Online notes that it can be), because, in common usage, a bio
is generally a page or so long, while the term biography
implies something much more comprehensive, and longer.
When used as a word prefix, bio- can refer to anything having to do with life, as it is an ancient Greek root meaning "life". (Hence, biology, biography, bionics, symbiosis etc.)
The Indo-European root of the Greek bio- is gwei[schwa]-* (Watkins, 33). What makes this etymological fact interesting is that gwei[schwa]- is also the root of the modern English words "grass", "vivid", "quick" (as in "The Quick and the Dead"), and, most interestingly, "whiskey" (the "water of life") (Ibid.)
*Of course, the proof for this fact is not straightforward; phonemic morphing over thousands of years makes some modern word connections less-than-obvious
Watkins, Calvert. The American Heritage Dictionary of Indo-European Roots. Boston: Houghton Mifflin, 2001. 150pp.
Merriam Webster Online, at www.m-w.com