You've seen your own blood, when you have a cut or a scrape. You can see the veins in your wrist, and you've seen the scab that forms as a cut heals. But do you know what blood does for you? Without blood, you couldn't play, or grow, or learn. That's because just about every part of your body needs blood, from your muscles to your bones to your brain. How does your body use blood? Read and find out!