Blood

• The job of red blood cells is to carry oxygen from the lungs to all the cells in the body.
• The shape of a red blood cell is a biconcave disc (like a doughnut) - this gives a large surface area for absorbing oxygen.
• Red blood cells do not have a nucleus - this allows more room to carry oxygen.
• Red blood cells contain a red pigment called haemoglobin. In the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin. In body tissues, the reverse happens - the oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen into the cells.
• Some white blood cells can change shape to gobble up unwelcome microorganisms, in a process called phagocytosis.
• Some white blood cells produce antibodies to fight microorganisms, as well as antitoxins to neutralise any toxins produced by the microorganism.
• Unlike red blood cells, white blood cells have a nucleus.
• Platelets are small fragments of cells. They have no nucleus. They help the blood to clot at a wound - to stop all your blood pouring out and to stop microorganisms getting in.
• A lack of platelets in your body could cause excessive bleeding and bruising.
• Plasma is a pale straw-coloured liquid which carries everything. This includes: red blood cells, white blood cells, platelets, nutrients like glucose and amino acids (these are soluble products of digestion which are absorbed from the gut and taken to the cells of the body), carbon dioxide (from the organs to the lungs), urea (from the liver to the kidney), hormones, proteins and antibodies and antitoxins (produced by the white blood cells).