MEDizzy - If the intracellular concentration of a membrane-permeant

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Membrane Physiology

If the intracellular concentration of a membrane-permeant substance doubles from 10 to 20 millimolar and the extracellular concentration remains at 5 millimolar, the rate of diffusion of that substance across the plasma membrane will increase by a factor of how much?

ExplanationNet diffusion of a substance across a permeable membrane is proportional to the concentration difference of the substance on either side of the membrane. Initially, the concentration difference is 5 millimolar (10 millimolar − 5 millimolar). When the intracellular concentration doubles to 20 millimolar, the concentration difference becomes 15 millimolar (20 millimolar − 5 millimolar). The concentration difference has tripled; therefore, the rate of diffusion would also increase by a factor of 3