tiny air pockets in the lungs. The blood gets oxygen in the alveoli.
beat:a steady rhythm of sound. The beat of your heart sounds like this: lub-dub, lub-dub, lub-dub.
carbon dioxide:a gas. Carbon dioxide is a waste in the blood stream.
center:a special place. There are centers in your brain for each of your senses.
cluster:a group of things that are alike. Many clusters of alveoli in your lungs help you breathe.
contract:to get shorter. When you move your arm, one muscle contracts while another stretches.
control:to tell what to do. Your brain helps control your muscles when you move.
energy:the power you need to move your body. Food gives your body energy.
exercise:to move your body. When you exercise, you make your heart pump faster.
germ:a small living thing that can make you sick. Some germs can give you a cold.
oxygen:a gas found in the air we breathe. The body needs oxygen to live.
pulse:a beat you feel in your arteries as your heart pumps. Your pulse speeds up when your heart beats faster.
pump:to move fluid. Your heart pumps blood through your arteries and veins.
system:parts of the body that work together to do a special job. Your skeleton is a system of bones.
vitamin:a natural material found in food that keeps the body healthy. Some vitamins are made within the body.
waste:something that is no longer needed. Carbon dioxide is a waste from your body.