Examine a prepared blood smear using a microscope.
The human body contains about five litres of blood. Blood is made up of two main parts: plasma and blood cells.
Plasma Plasma is the liquid part of the blood, composed mainly of water. It is straw coloured and makes up about half of the blood volume.
l
l l l
l Platelet
Red blood cell
White blood cell
Fig. 3 Red and white blood cells and platelets.
Haemoglobin The molecule that allows red blood cells to carry oxygen to other cells in the body.
Fig. 4 Red blood cells.
Functions of plasma Transports dissolved nutrients from the digestive system to the rest of the body. Transports wastes for removal. Transports carbon dioxide from the body to the lungs. Contains special proteins that can clot the blood to prevent blood loss. Transports heat around the body.
Plasma
Blood cells
Fig. 2 Both test tubes contain whole blood. In the test tube on the right plasma and blood cells have been separated.
Blood cells Blood cells are suspended in the plasma. Blood cells are produced in the bone marrow of long bones, such as the thigh bone (femur) and the pelvis.
There are three types of blood cell.
1. Red blood cells These are the most common type of blood cell. One drop of blood contains about 5 million red blood cells. They are disc- shaped with a dip in the middle. This allows them to bend and fit into tiny blood vessels. They do not have a nucleus. Red blood cells give blood its red colour due to the molecule haemoglobin which can bond to oxygen. Blood that is rich in oxygen is a bright red colour. When it has lost most of its oxygen it is a darker red colour.
Function of red blood cells: Transport oxygen from the lungs to the rest of the body.
