Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells suspended in blood plasma.
Blood is made mostly of plasma, but 3 main types of blood cells circulate with the plasma:
Platelets help the blood to clot. Clotting stops the blood from flowing out of the body when a vein or artery is broken. …
Red blood cells carry oxygen. …
White blood cells ward off infection.
