Red blood cells
Red blood cells are adapted to carry oxygen from the lungs to tissues around the body:
Biconcave disc shape: increases surface area for oxygen diffusion to and from red blood cells.
This shape also allows red blood cells to bend, necessary for squeezing through capillary vessels.
- Have no nucleus: increases the space inside the cell to carry oxygen.
- Contain haemoglobin: an iron-containing pigment that binds to oxygen.
Much of the iron we need in our diet goes into producing haemoglobin.
The colour of blood depends on whether the haemoglobin in red blood cells is bound to oxygen. Oxygen-bound haemoglobin is bright red, while unbound haemoglobin is darker.