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.

Diffusion pressure alone becomes insufficient for oxygen delivery to all body parts in large animals.