Albumin contributes the maximum to oncotic pressure because:

Albumin contributes the maximum to oncotic pressure because it has:

A. High molecular weight, low concentration
B. Low molecular weight, low concentration
C. High molecular weight, high concentration
D. Low molecular weight, high concentration

Answer is D. Low molecular weight, high concentration.

By principle, Osmotic pressure is determined by the number of particles in solution and not by the mass of the particle. And hence, 1 gm of a heavy molecular weight protein will contain fewer number of particles as compared to a light molecular weight protein, and consequently will have a lesser osmotic pressure.

Proteins in Plasma          Molecular Weight          Oncotic P. Contribution

Albumin                                     69,000                                  80 percent
Globulin                                   140,000                                  20 percent
Fibrinogen                                400,000                                   0 percent

Thus, we see that albumin which has the lowest molecular weight contributes maximally to the plasma oncotic pressure.