[Campbell Biology P.190] Cotransport is a type of active transport where ATP is not directly... | Practice Question

Cotransport is a type of active transport where ATP is not directly hydrolyzed by the cotransporter protein. Why is cotransport still considered a form of active transport?

  • A: Because it relies on the diffusion of a substance down its concentration gradient.
  • B: Because it moves both solutes against their concentration gradients simultaneously.
  • C: Because the 'downhill' diffusion of one solute, which provides the energy, was established by a primary active transport process that *did* directly use ATP.
  • D: Because it is a form of facilitated diffusion that uses two different solutes.

Explanation

Cotransport is considered active transport because the 'downhill' diffusion of one solute, which provides the energy for the 'uphill' transport of the other, was itself established by a primary active transport mechanism that directly consumed ATP. Thus, the energy for cotransport is indirectly derived from ATP hydrolysis.