Answer: Sodium-Potassium pumps (NaK Pumps)
Explanation:
So you only need to consider two things:
Are these ions mainly found on the inside or outside of the cell?
What are the ions' charges?
The location of the ions: Sodium is mostly found outside of the cell.
Potassium is mostly found inside of cells.
Sodium and potassium both have a positive charge.
So, consider this: what does sodium want to do? It wants to RUSH INTO the cell for two reasons: there is more on the outside, and the inside of the cell is negatively charged, which attracts it.
Potassium wishes to do the direct opposite. It is mostly inside the cell and wants to get out. Also, because opposite charges repel each other, potassium wishes to leave the cell.
Okay, so sodium enters the cell and potassium exits. What is it that keeps them where they are?
The sodium-potassium pumps. They take out sodium to keep it outside the cell and bring potassium back in. This is what it means to "maintain a steady state resting membrane potential."
It's three sodium ions leaving and two potassium ions entering per "pump."
