Circulatory System - The Blood

1) The red blood cells carry oxygen from the lungs to all the cells in the body.

2) They have a doughnut shape to give a large surface area for absorbing oxygen.

3) They don't have a nucleus - this allows more room to carry oxygen.

4) They contain a red pigment called haemoglobin.

5) In the lungs, haemoglobin combines with oxygen to become oxyhaemoglobin. In body tissues, the reverse happens - oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen to the cells.

1) They can change shape to "gobble up" unwelcome microorganisms.

2) They produce antibodies to fight microorganisms, as well as, antitoxins to neutralise any toxins produced by the microorganisms.

3) Unlike red blood cells, they do have a nucleus.

1) These are small fragments of cells. They have no nucleus.

2) They help the blood to clot at a wound - to stop all blood pouring out and to stop microorganisms getting in.

3) Lack of platelets can cause excessive bleeding and bruising.

This is a pale straw-coloured liquid which carries just about everything:

1) Red and white blood cells and platelets.

2) Nutrients like glucose and amino acids. These are the soluble products of digestion which are absorbed from the gut and taken to the cells of the body.

3) Carbon dioxide from the organs to the lungs.

4) Urea from the liver to the kidneys.

5) Hormones

6) Antibodies and antitoxins produced by the white blood cells.