Answer:
In passive transport, substances simply move from an area of higher concentration to an area of lower concentration, which does not require the input of energy. Concentration gradient, size of the particles that are diffusing, and temperature of the system affect the rate of diffusion.
In active transport, the particles move across a cell membrane from a lower concentration to a higher concentration. Active transport is the energy-requiring process of pumping molecules and ions across membranes "uphill" against a gradient.
