What is blood made of?
Blood is a complicated mixture of liquids, chemicals and cells. If you could separate out the ingredients in a single drop of blood, you would find that just over half of it is made of liquid called plasma. Plasmas consists mainly of water, but it also contains many dissolved chemicals. One of these is glucose, the substance that your body uses to make energy. The rest of the drop of blood would consist of millions of cells so tiny that they can only be seen under a microscope. Most of these cells are the red blood cells, which carry oxygen. Scattered among them are transparent cells called white cells, which are involved in fighting disease. Red blood cells are shape like tiny coins. White blood cells are bigger, and many can move about by changing shape.