What blood actually does
Biology · Key Stage 2 · The School
A delivery system
Blood is not just red liquid that appears when you are cut. It is a delivery system for your whole body. It carries things your body needs to where they are needed, and carries waste away again. It flows around the body constantly, day and night. Even while you sleep, blood keeps moving without stopping.
Red blood cells
RED BLOOD CELLS are the most common cell in blood. Their main job is carrying OXYGEN. They pick oxygen up in the lungs and carry it to every part of the body. Without them, your body parts could not get the oxygen they need. Red blood cells are also what gives blood its red colour.
White blood cells and plasma
WHITE BLOOD CELLS have a different job. They fight off germs that get into the body. PLASMA is the pale yellow liquid that everything else floats in. It carries digested food and other useful things around the body too. Without plasma, none of the other parts of blood could travel anywhere at all. There are far fewer white blood cells than red ones in a healthy body.
You cut your finger. Germs try to get in through the cut. WHITE BLOOD CELLS rush to the area and attack them. Meanwhile, RED BLOOD CELLS keep carrying oxygen everywhere else in your body, as normal. PLASMA carries useful nutrients past the cut too, on its way to cells that need them. Three different jobs, all happening inside the very same drop of blood, at the very same time.