Explain how the structure of red blood cells makes them well suited to carrying oxygen around the body.

Red blood cells are biconcave discs, which gives them a very large surface area relative to their volume. This high surface‑area‑to‑volume ratio allows oxygen to diffuse into and out of the cell very quickly.

They contain large amounts of haemoglobin. Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin, which is the form that carries oxygen through the bloodstream.

Red blood cells lack a nucleus and most organelles. The absence of a nucleus frees up space inside the cell for haemoglobin, so each cell can carry more oxygen.

When the blood reaches tissues, oxyhaemoglobin releases its oxygen. The released oxygen then diffuses into the cells, enabling aerobic respiration.

These structural features together make red blood cells highly efficient at transporting oxygen around the body.