Using billions of tiny tubes, your body is constantly pumping blood throughout your body. On the way out, your blood is loaded with the things that your body needs, like food, oxygen, and other chemicals. On the way back, your blood is full of things that the cells of your body need to get rid of, like waste.

What color is blood? Well, that depends. Sometimes it is red, and sometimes it is blue. Don’t believe me? Look at your arm. Better yet, look at the arm of one of your parents. Can you see the blue veins? Why are they blue? When blood is full of oxygen it is red, but when it is low on oxygen it turns bluish. Why don’t I ever see blue blood? Because as it leaves your body, it quickly turns red, as it takes in oxygen.