Fourth Grade
Worksheets
Your Blood's Other Job
Caption: This is a scanning electron microscope image of normal circulating human blood. One can see red blood cells, several white blood cells, and many small disc-shaped platelets. Picture by Bruce Wetzel and Harry Schaefer for the National Cancer Institute.
You already know that your blood takes nutrients and oxygen to all your body's cells. That is the job of the red blood cells. But did you know that your blood has another job? Blood also fights off disease-causing germs.
The blood's white blood cells attack germs that get inside your body. White blood cells are like your body's army. They fight invaders that do not belong inside you. White blood cells surround the germs and swallow them.
Your blood also has antibodies. White blood cells attack germs. Antibodies are proteins that join in the fight. There are exact antibodies that fight exact germs. Antibodies stay in your blood, sometimes forever. The white cells and the antibodies are part of your body's immune system.
Let's say that your body is invaded by the germs that cause chicken pox. The white cells attack the chicken pox germs. Your body makes antibodies that will fight the chicken pox germs, too.
