Some carriers move two solutes in opposite directions
- The idea
- Predict
- See it
- Why
- Check
The idea
“When a carrier moves two solutes together, they both cross in the same direction.”
Coupled transport sounds like two passengers riding through one door together. Some carriers work that way. Others trade one solute for another.
The short version
The mistake: When a carrier moves two solutes together, they both cross in the same direction.
What's actually true: A symporter moves two solutes the same way, and an antiporter moves them in opposite directions.
- In cotransport, one solute flows down its gradient through a carrier. That energy moves a second solute, often against its gradient.
- A symporter moves both solutes the same way. An antiporter, or exchanger, moves them in opposite directions.
- Sym means together, and anti means against. The sodium-potassium pump is also an antiporter, but it runs on ATP.
On the exam: Track each solute's direction. Same way is symport. Opposite ways is antiport.