Red blood cell, artwork. Section through a human red blood cell (erythrocyte). The upper half of the image shows the blood serum, the lower half shows the erythrocyte. The erythrocyte consists of a cell wall (mauve) and haemoglobin molecules (red) which act as a carrier of oxygen to all parts of the body. The serum contains antibodies (Y-shaped molecules), long thin fibrinogen molecules (light red), albumin (dark yellow), complement C1 (6-armed structures) and lipoprotein (blue).