Blood consists of red and white blood cells and platelets floating in watery plasma.Blood carries food and oxygen all around the body and takes away waste substances. Pumped by the heart, blood travels through a complicated network of blood vessels to reach every cell in the body. Seen through a microscope, blood is made up of millions of tiny cells floating in a yellowish, watery fluid called plasma. Nutrients from your food are dissolved in the plasma, while oxygen is carried by the red blood cells.
Red and white blood cellsBlood contains three types of cell: red cells, white cells and platelets. Red cells are used for carrying oxygen. They are shaped like doughnuts. They contain haemoglobin, a substance that combines easily with oxygen. White cells fight infection from bacteria or viruses that have invaded the bloodstream. They find the invaders, surround them and swallow them up.
There are about 5 litres (9 pints) of blood flowing around an adult's body.
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