Understanding Blood Cells (Part 1)
Blood cells have several kinds, each of which are essential for a body to function properly. These are the erythrocytes or red blood cells, leukocytes or white blood cells, and platelets.
Erythrocytes contain hemoglobin, which is the substance that transports oxygen to the different parts of the body. This is why a person with anemia experiences shortness of breath and fatigue, because the vital organs do not get enough oxygen.
Leukocytes fight infections in the body. It has sub-types: granulocytes that develop to neutrophils, basophils, and eosinophils which destroy bacteria and fight infections; and lympoid cells that develop to monocytes and lymphocytes.
(source)