In mammals, blood consists of plasma, red blood cells and white blood cells.
Nutrients (eg glucose and amino acids), oxygen and carbon dioxide are transported around the body in the blood.
Red blood cells transport oxygen around the body. They are specialised to carry oxygen because they:
Haemoglobin binds with oxygen in body locations where the oxygen concentration is high (in the lungs) and forms oxyhaemoglobin.
Blood with a high concentration of oxygen is described as oxygenated.
This makes the blood a bright red colour.
In locations where the oxygen concentration is low (body tissues) haemoglobin releases oxygen.
The oxygen then diffuses into the cells. Blood that has a low oxygen concentration is a dark red colour and is described as deoxygenated.
White blood cells are part of the immune system and are involved in destroying pathogens (disease-causing micro-organisms bacteria, viruses and fungi).
There are 2 main types of cells involved:
Antibodies are specific to particular pathogens.