Originally Answered: Scientific book a teenager could read?
I'll second the nomination for A Short History of Nearly Everything, by Bill Bryson. My brother bought it for me as a Christmas present, and I've already finished- I really enjoyed it.
You should also check out the following youtube channels. They're all very reputable:
Crashcourse: it has a 40-part biology series, which it sounds like you'd enjoy, and is about halfway through a 12-week series on ecology.
Veritasium: Derek, who has a PhD on educational science films, teaches about all kinds of cool topics - the physics of a slinky, how trees move water up their trunks, etc. - in videos that are just a few minutes long. Sometimes he interviews random people and asks them about scientific topics, to illustrate popular misconceptions.
Sixty Symbols: A channel about particly physics and astronomy (the two size extremes!). Brady, the cameraman, interviews scientists/professors at the University of Nottingham, asking them to explain all kinds of concepts, from Falling into black holes to rainbows to magnets.
Nottingham science: Miscellaneous science videos, again based on video interviews involving staff at U of Nottingham.
Periodicvideos: A channel that focuses on chemistry, from explaining the properties of certain elements to examining the effect of acids and bases on a coke can. You've gotta check this channel out just for the professor's hair. It is....just...wow.
Smarter Every Day: Destin, a light-hearted and fun science admirer posts videos on topics about all kinds of scientific concepts, from how cats always land on their paws to the physics of helicopter flying.
Minutephysics- Henry discusses and teaches physics concepts in videos ranging from 1 to 5 minutes. I find most of his videos a little fast-paced to follow, but they are cool.
Finally, scishow- Hank Green (the same person from Crashcourse) posts miscallenous and awesome science vids.
Just search the channel names on youtube and you should find them. Enjoy!
Oh, I almost forgot, check out the sportsscientists.com to learn about running/biking physiology. They don't post much anymore, but the authors have PhD's in, I believe, Exercise Physiology. Check out their highlights/series section.