Final answer:
In passive transport, a charged solute moves spontaneously down its electrochemical gradient, considering both the concentration and electrical gradients affected by the ion's charge.
Step-by-step explanation:
In passive transport, a charged solute moves spontaneously down its electrochemical gradient. This means that along with the concentration gradient, the electrical gradient is also considered because of the charge on the ions. Both these gradients combined determine the movement of ions across a cell membrane. The solute will tend to move from a region where it has a higher electrochemical potential to a region with lower potential, which often includes movement from an area of higher concentration to an area of lower concentration and from an area with opposite charge towards like charge.
Simple diffusion is a subset of passive transport, which applies to noncharged molecules moving down their concentration gradient without the need for additional energy. In contrast, an electrochemical gradient includes both chemical (concentration) and electrical gradients for charged molecules such as ions.