Here's something that might interest you, it's an article from Sky and telescope magazine about the possibility of habitable moons in orbit around gas giants. http://skyandtelescope.com/resources/seti/article_255_1.asp
If I recall correctly from last year's biology plants don't know which way's up and which way's down. But the plant growth hormone (Axin or something like that) gathers at the bottom of the seed (pulled down by gravity) and that causes the plant to "know" which way's up. The plants roots then...