Final answer:
Passive transport, such as diffusion, occurs naturally without energy input. In diffusion, substances move from an area of higher concentration to an area of lower concentration.
Step-by-step explanation:
Diffusion is a passive process of transport. A single substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across a space. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement.
In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion. Diffusion is a form of passive transport because it occurs naturally without the input of energy. In contrast, active transport requires energy input to transport molecules.
The term "passive" in passive transport means that the process occurs naturally without an input of energy from the cell. In diffusion, a form of passive transport, molecules move from an area of higher concentration to an area of lower concentration until the concentration levels are equal across a space. This process is driven by the kinetic energy of the molecules and is fundamental in numerous biological functions, such as the exchange of O2 and CO2 in the lungs and the distribution of nutrients and waste products within the cell's cytosol and across the plasma membrane.