The left atrium collects oxygen-rich blood from the lungs, and upon contraction, transfers it to the left ventricle. The left ventricle then pumps the oxygenated blood to the rest of the body.

The heart has different chambers to prevent the mixing of oxygen-rich and carbon dioxide-rich blood. This separation ensures efficient oxygenation and removal of carbon dioxide.

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.