<prompt> Diffusion through a membrane is affected by all except:TemperatureMembrane pore sizeSize of the particleConcentration gradient across the membrane  <response>: Ans c Size of the particle Ref: Vasudevan, 4th ed, p. 13, Guyton, 9th ed, p. 48, Ganong, 22nd ed, p. 4Judging 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 sizepage 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 temperatureDiffusionIt 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 Ficks law of diffusion.Ficks law of diffusionJ - DA J is the net rate of diffusionD is the diffusion coefficientA is the areaDCDX is the concentration gradientThe minus indicates the direction of diffusion. 