Final answer:
Passive transport is a naturally occurring phenomenon that does not require energy input from the cell. Examples include diffusion and facilitated diffusion.
Step-by-step explanation:
Passive transport is a naturally occurring phenomenon that does not require the cell to exert any of its energy to accomplish the movement of substances.
Examples of passive transport include diffusion, where molecules move from an area of high concentration to an area of low concentration, and facilitated diffusion, where molecules move down a concentration gradient through specific protein channels in the cell membrane.
Passive transport does not require transport proteins, facilitation by enzymes, an isotonic solution, or energy from the cell.