Hi Natasha,

I would say for the MCAT, I would be hard pressed to find something that travels by active transport that travels with its concentration gradient, because then you would probably do facilitated diffusion and save the energy. In addition, active transport is defined as the transport of substances against their concentration gradient.

For secondary active transport, you use the favorable gradient of one species to drive the transport of another species against its gradient, so this is also a case of driving the ion of interest against its gradient using some form of energy.

Of course, it might still be possible, I just think it is unlikely you would be expected to know this without passage prompting.

Please let me know if this is unclear,

Katt