Many solutes that must move into and out of cells exist in either a protonated o

Question

Many solutes that must move into and out of cells exist in either a protonated or ionized form, or they have functional groups that can be either protonated or ionized. Simple molecules such as CO_2, H_3PO_4 (phosphoric acid), and NH_3 (ammonia) are in this category, as are organic molecules with carboxylic acid groups, phosphate groups, and/or amino groups. For a cell that must take up ammonia from its environment, will uptake of the charged form require more or less energy than uptake of the uncharged form, assuming that the cell has a negative membrane potential? Explain your answer Drag the terms on the left to the appropriate blanks on the right to complete the sentences. To say that the cell has a negative membrane potential means that the surface of the plasma membrane has a more negative charge than the surface. A solute such as will therefore be drawn inward by the membrane potential, which means that uptake of across the plasma membrane will require more energy than the uptake of assuming the same concentration gradient for the two solutes, of course.

Explanation / Answer

Answer

To say that the cell has a negative membrane potential means that the Inner surface of the plasma membrane has a more negative charge than the outer surface. A positively charged solute such as NH4 + will, therefore, be drawn inward by the membrane potential, which means that uptake NH3across the plasma membrane will require more energy than the uptake of NH4+ assuming the same concentration gradient for the solute of course.

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