A pumping organ is needed to push blood around the body, and the network of tubes ensures the distribution of blood to all tissues, providing nutrients and oxygen.

Oxygen is carried by red blood corpuscles in the blood.

Plasma is the fluid medium in blood, transporting food, carbon dioxide, nitrogenous wastes, salts, and other substances in dissolved form.

Carbon dioxide, more soluble in water than oxygen, is mainly carried in its dissolved form in the blood.

Haemoglobin, a respiratory pigment in red blood cells, has a high affinity for oxygen, facilitating its transport from the lungs to oxygen-deficient tissues.