2.59 explain how adaptations of red blood cells, including shape, structure and the presence of haemoglobin, make them suitable for the transport of oxygen

Red blood cells have a little dent in the middle (a bi-concave shape). This makes for a large surface area for the absorption and release of oxygen. They dont have a nucleus which frees up space for haemoglobin. In the lungs, haemoglobin reacts with oxygen to become oxyhemoglobin, this reaction reverses when the blood reached tissue cells and the oxygen is released.