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Secondary Active Transport

Is an external source of energy always needed to drive active transport? In some cases it is possible to couple the transport of two different molecules across a membrane so that the energetic effects cancel one another out. One molecule is moving down a concentration gradient (thus reducing potential energy). This molecule reacts with the transport protein to change its conformation and transport the second molecule across the membrane against its concentration gradient. Thus the energy is transferred from one concentration gradient to the transport protein and then to a second concentration gradient. In this case the ultimate source of energy is the force causing the initial concentration gradient.

View the animation below, then complete the quiz to test your knowledge of the concept.






1In human systems...
A)sodium has a higher concentration in the intracellular fluid of the cell.
B)sodium has a higher concentration in the extracellular fluid of the cell.
C)sodium maintains equilibrium between both sides of the cell membrane.
D)sodium is found as an integral part of the cell membrane.
E)sodium is a carrier molecule in the cell membrane.



2Sodium will easily...
A)diffuse from the extracellular fluid to the intracellular fluid.
B)diffuse from the intracellular fluid to the extracellular fluid.
C)be actively transported from the extracellular fluid to the intracellular fluid.
D)be actively transported from the intracellular fluid to the extracellular fluid.
E)maintain equilibrium via the sodium-potassium pump.



3Due to these characteristics of sodium...
A)as the sodium maintains equilibrium, this allows other molecules to move into and out of the cell.
B)as sodium is actively transported out of the cell, it brings other molecules with it.
C)as sodium is actively transported into the cell, it brings other molecules with it.
D)as the sodium diffuses out of the cell, it brings other molecules with it.
E)as the sodium diffuses into the cell, it brings other molecules with it.



4Unlike primary active transport, secondary active transport does not require an ATP molecule to function.
A)True
B)False



5Unlike primary active transport, secondary active transport does not require a specialized structure for cell membrane transport.
A)True
B)False







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