Final answer:
Passive transport is influenced by molecule size, temperature, concentration gradients, and membrane permeability; it allows substances to move down their concentration gradient through diffusion without requiring energy.
Step-by-step explanation:
The overall direction of passive transport also depends on factors like the molecule's or ion's size, the temperature of the system, the substance's concentration gradient, and the membrane's selective permeability. In passive transport, substances move from an area of higher concentration to an area of lower concentration until they are evenly distributed. This process can occur through simple diffusion for small, uncharged molecules, or through facilitated transport using specific protein channels for larger or polar molecules like glucose, without requiring energy from the cell. Factors such as particle size and temperature can influence the efficiency and rate of passive transport.