Concentration of urea on one side (side A) of permeable membrane is 20 and on other side (side B) is 40. If concentration on side A is increased to 40, what will happen to rate of diffusion?

Ans. is 'c' i.e., It will be zero [Ref: Principles of medical physiology p. 71)This question, the concentration gradient is zero as both sides (A & B) have same concentration (40) of urea.Thus there is no diffusion + Rate of diffusion is zero.