Plasma is approximately 90% water and 10% dissolved organic and inorganic compounds.

The organic materials include proteins such as globulins (alpha, beta, gamma and immunoglobulins), albumins, clotting factors and antibodies.

Serum is a straw-coloured liquid which remains after blood has clotted.  Its composition is therefore the same as that of plasma, but without the clotting factors.

Definitions

ALBUMIN: Group of several small proteins, forming a large part of the plasma protein content. They are responsible for the transport of free fatty acids.

CLOTTING FACTORS: Proteins in the blood which are involved in the complex process of converting soluble fibrinogen into fibrin.

SERUM: The fibrinogen-free fluid fraction of blood or haemolymph. In vertebrates, the blood is first allowed to clot (i.e. fibrinogen is converted to insoluble fibrin) and then centrifuged to remove blood cells and fibrin.