Digestion, breathing and clean habitats

Your body needs oxygen, a gas in the air, to get energy from food. You breathe in through your nose or mouth. The air goes down the windpipe, which divides into branching tubes that lead into the two lungs. In the lungs, oxygen passes into the blood, and the blood carries it round the body. The blood also brings back a waste gas called carbon dioxide, and you breathe it out. Under the lungs there is a flat muscle called the diaphragm. When you breathe in, it moves down, your chest gets bigger and air flows in. When you breathe out, it moves up and the air is pushed out. A fish breathes too. Water flows over its gills, and the gills take oxygen from the water into the fish’s blood.