Science Fair Experiment!?!?! HELP!!?

I need 3 ideas for my Biology Honors 9th Grade Science Fair. They need to be experiments ( trials ). Like with IV and DV, Constants, Hypothesis, Title, etc. I just need 3 very good ideas. Not things like using paper airplanes or plants. THX!!! BTW I go to Fairfax High School in Fairfax, VA if that helps at all.