That's tough about your dad, sorry to hear that...a steady and supportive father figure in life is extremely important. Are there any other mentors you can lean on? Not as a substitute, but as a supplement? Also, I don't want to dismiss what you're saying at all as it is very important and the feelings you have are VERY real. But, if you are a freshman in high school then at your age hormones are screaming and going wild all over the place. The worst bout of depression I had was close to your age and I'm sure that was part of it for me. With time, those hormones will tone down a bit and you may see improvement, but again it doesn't matter because you feel what you feel. You are right to say that people will not understand you, only you can understand you and how you feel. But, that doesn't mean that others don't care about you, so try not to shut them out if you can. I'm not sure if you tend to do that or not, but I've seen it and experienced it, and if you isolate yourself then the lonely feeling only gets worse.
Biology huh? Tough subject, I actually majored in it in college my first year and decided to change majors at the end of the year. Fascinating subject though!