Transport of Na+ and Ca2+ across the plasma membrane is an example of
- A.antiport
- B.symport
- C.uniport
- D.aquaporins
Correct answer
Explanation
The correct answer is A, antiport. In the sodium-calcium exchanger, Na+ ions enter the cell while Ca2+ ions are pushed out, so the two ions cross the membrane in opposite directions.
Carrier proteins in the plasma membrane are grouped by how they move solutes. A uniporter moves one kind of molecule in one direction. A symporter moves two different solutes together in the same direction, as when glucose enters intestinal cells along with sodium. An antiporter moves two solutes in opposite directions at the same time. The sodium-calcium exchanger of heart muscle and nerve cells uses the inward flow of sodium down its gradient to throw calcium out of the cell, which helps the heart muscle relax after each beat.
B is wrong because a symport carries both ions the same way. C is wrong because a uniport carries only one kind of solute. D is wrong because aquaporins are channels that let water, not these ions, through the membrane.
Exam tip: uniport one solute, symport same direction, antiport opposite directions; Na+/K+ pump and Na+/Ca2+ exchanger both move ions in opposite ways.
Practice Questions
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- A.25°C
- B.37°C
- C.500°C
- D.1500°C
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Show answer
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