Final answer:
Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. This random movement can result in a net movement of ions across a membrane due to concentration gradients. This process is known as passive diffusion and can lead to the generation of a voltage across the cell membrane.
Step-by-step explanation:
Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. While the movement itself is random, over time, more molecules tend to be propelled into the less concentrated area, resulting in a net movement of molecules. This principle applies to the movement of ions across a membrane as well. For example, in passive diffusion, certain ions, such as potassium and chloride, can diffuse across a cell membrane based on their concentration gradients. As a result, a voltage is generated across the cell membrane due to the imbalance of positive and negative charges.