Answer:
Nine
Explanation:
These are called carrier proteins, and they have what it is called: solute-binding sites, that when saturated, they are considered "full".
Each different amino acid needs a separate carrier protein to move it across the plasma membrane, so that's 3, then the four different sugars need separate carriers as well, we add 4 more then, we have 7 so far, finally the 2 different ions use 2 more, plus the other 7, totals 9.