Hello!

Sorry for the super late reply. I've been travelling a lot in regions with spotty wifi.

Anyway about your question.

I've looked back at the lectures, but I can't find where I said there are two ATP molecules required for Na/K pumps.

One phosphate molecule from ATP binds to the protein to allow the movement of sodium ions across the membrane.

After the release of sodium, then binding of potassium ions, the phosphate group detaches from the protein

allowing it to return to its original configuration, allowing the movement of potassium into the cell.

This overall process of moving sodium and potassium ions requires one ATP molecule

therefore it is active transport that requires energy.

Moving potassium ions is still considered required energy because its moving ions against the concentration gradient.

The movement of the two ions are linked for this protein interaction, meaning one cannot occur without the other.

You can state hypotheticals about how the returning of the protein, thus moving of potassium occurs due to the phosphate group detaching,

therefore does not require energy, but the reason its "returning" to base state is because energy was used at the onset.

My opinion is that defining movement of potassium as not requiring energy is unhelpful and needlessly pedantic in understanding this chapter,

(which I should add, it seems like you already have a fairly strong grasp on!) so you shouldn't spend any time on it. At least if your focus is on AP Bio.

I hope this clears things up.

Get back to me if you are still confused! :D