Diffusion through a membrane is affected by all except:

Ans c (Size of the particle) Ref: Vasudevan, 4th ed, p. 13, Guyton, 9th ed, p. 48, Ganong, 22nd ed, p. 4(Judging by the number of references, you can see that finding the answer to this question was not as easy as it looked!)Diffusion is affected by concentration gradient, temperature, and membrane pore size.The text given in Guyton about molecular size appears confusing, but it is clearly stated in Vasudevan and Sreekumari that "permeability does not depend on molecular size"(page 13).Many would have gone for option c -Temperature, but it is clearly stated in Guyton (page 48) that "Greater the temperature, greater is the thermal motion of molecules and ions in a solution, so that diffusion increases directly in proportion to temperature"DiffusionIt is the process by which a gas or a substance in solution expands, because of the motion of its particles, to fill all of the available volume. Diffusion through a membrane depends on various factors. The concentration gradient is one of the most important factors that affect diffusion. The other factors are cross sectional area, thickness of the membrane, temperature and membrane pore size. Diffusion is guided by the Fick's law of diffusion.Fick's law of diffusionJ = - DA J is the net rate of diffusionD is the diffusion coefficientA is the areaDC/DX is the concentration gradientThe minus indicates the direction of diffusion.