This was on my google homepage:
I am alive and growing and am used mainly for support;
but when I die I can be used in a variety of ways.
I am a protector of important parts,
much of me is never seen;
except when my owner is happy, angry or eating.
What am I?
Would it help if I told you the title of the riddle was called "The Osteon Factor"?
...And that I just had a test on it?
Yeah, nerdy, I know.