out o

Primary active transport (against electrochemical gradient)

Ion o

Ion Secondary active transport (against electrochemical gradient, driven by ion moving down its gradient)

FIGURE 11-26 Summary of transport types.

Before equilibrium Net flux

C1 = C2

At equilibrium No net flux

Before equilibrium

At equilibrium

FIGURE 11-27 Movement of solutes across a permeable membrane.

(a) Net movement of electrically neutral solutes is toward the side of lower solute concentration until equilibrium is achieved. The solute concentrations on the left and right sides of the membrane are designated C| and C2. The rate of transmembrane movement (indicated by the large arrows) is proportional to the concentration gradient, C1/C2. (b) Net movement of electrically charged solutes is dictated by a combination of the electrical potential (Vm) and the chemical concentration difference across the membrane; net ion movement continues until this electrochemical potential reaches zero.

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