Circulatory System

Blood Blood Vessels Heart

composition and function of blood

OB13 describe the function and composition of blood, know that blood contains white blood cells, red blood cells and platelets in a liquid called plasma

white blood cells,

  • The function of white blood cells is to fight infections. These Infections maybe caused by bacteria or viruses. If it is a bacterial infection then anti-biotics may be used to assist the white blood cells do their job. Antibiotics will have no effect on viruses. You can learn more about bacteria and viruses hereWhite blood cells are made in the inside of bones, in a substance called bone marrow.
  • They live for only a matter of days.
  • They are twice as big as red blood cells but have no definite shape.
  • There are very few WBCs when compared to the number of RBCs.

red blood cells

The function of Red blood cells is to carry oxygen around the body. They deliver oxygen to every cell in the body as so the cells can carry out their jobs.

Red blood cells are again made inside the bone marrow, they need an important chemical called haemoglobin, without this chemical their ability to carry oxygen is lessened. Haemoglobin requires iron, and so this is a very important mineral in a persons diet.

They each have a regular shape, if you look from above a cell it looks like a round disk, that is thicker on the outside. From the side it looks curved, like taking a slice from the top of a grape, it has a bag like structure.

Carbon monoxide poisioning is caused by the fact it too latches on to haemoglobin too like oxygen.


Platelets are small fragments of bone,

they are called into action when we have a cut.

If the cut is held closed under pressure, by a bandage (or otherwise) the platlets have a chance to form a scab.

This scab prevents further loss of blood and also forms a barrier to prevent infections entering the body.

The big bluey blobs are White Blood Cells, the red disks are Red Blood Cells and the small segments are platlets.


Plasma is a pale yellow liquid that suspends all the particles of blood.