Final answer:
Passive transport for uncharged molecules is determined by the concentration gradient, while for charged molecules it is determined by the combined effect of the concentration and electrical gradients called the electrochemical gradient.
Step-by-step explanation:
Passive transport for uncharged and charged molecules is determined by the concentration gradient and the electrochemical gradient.
For uncharged molecules like gases and lipids, they can diffuse through the cell membrane based on their concentration gradient. This means they move from an area of higher concentration to an area of lower concentration.
For charged molecules like ions, their movement is influenced by both the concentration gradient and the electrical gradient. The electrical gradient is created by the difference in charge across the membrane.
The electrochemical gradient is the combined effect of the concentration gradient and the electrical gradient. It determines the overall direction of movement for charged particles. If the concentration gradient is higher in one direction and the electrical gradient is also in the same direction, the particle will move in that direction. If the two gradients are in opposite directions, the net movement of the particle will depend on the relative strength of the gradients.