It's a cliche to say that we spend at least one-third of our lives asleep, but it's true, which probably explains why it's a cliche. Anyway, check out any or all of the following videos on the sleep cycle. They're all relatively short and the more sources you have the better it'll stick!
"The Sleep Cycle" a slow-moving cartoon, but will help
"The Sleep Cycle", not as slow, but with bizarre choice of music
SUPER SHORT! 30 seconds!!!! Sleep Cycle and more
Guess what? Bad things can happen when you don't get enough sleep! Although there isn't a one among you that has ever fallen asleep in my class, you know it happens. Check out this 4 minute NPR podcast on teens and their sleep deficit. There's also a really good Q & A section on the same topic, give it a once over.
And, finally, what would happen if you stayed up for 8 days straight? Staying up 24 hours straight has the same impact as being totally drunk (legally), so how 'bout 8 days? Find out by watching a little overview of the famous sleep deprivation experiment by Peter Tripp, a dj trying to raise money for a charity. Also check out this creepy little retelling of the experiment, shockingly there's actually more information about what happened to poor Tripp afterwards.