All are factors determining diffusion across membrane except
Correct Answer: Particle size
Description: Ans b (particle size) Ref: Vasudevan 4th ed pg J3, Guyton 48, Ganong 22nd ed pg 4)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 andSreekumari 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 factor 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 diffusion J = - 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.
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