Hemoglobin, a globular protein
green = haem (or heme) groups
red & blue = protein subunits

A scanning electron microscope (SEM) image of a normal red blood cell (left), a platelet (middle), and a white blood cell (right)

Blood is a liquid in humans and many animals. Blood is pushed through the organism by the heart. It brings nutrients and oxygen to the tissues of the body. It also takes away waste and carbon dioxide from tissues.

Blood is made up of blood plasma and various cells. These include red blood cells, white blood cells and platelets. Platelets help blood to clot. Hemoglobin is in red blood cells. White blood cells help fight infections and heal wounds.