How does active transport differ from passive transport?

Active transport requires energy to move substances across a cell membrane, while passive transport does not.

Active and passive transport are two fundamental methods that cells use to move substances across their membranes. The key difference between the two lies in whether or not the process requires energy. Active transport is a process that requires energy (in the form of ATP) to move substances against their concentration gradient, from an area of lower concentration to an area of higher concentration. This is often necessary when a cell needs to accumulate specific molecules, such as ions, glucose or amino acids, inside the cell.

On the other hand, passive transport does not require any energy. Instead, it relies on the natural movement of particles from an area of higher concentration to an area of lower concentration, a process known as diffusion. This can occur directly across the phospholipid bilayer of the cell membrane (simple diffusion) or through specific protein channels (facilitated diffusion). Osmosis, the diffusion of water across a selectively permeable membrane, is also a form of passive transport.

In summary, while both active and passive transport are essential for the functioning of cells, they differ significantly in their mechanisms and energy requirements. Active transport utilises energy to move substances against their concentration gradient, while passive transport relies on the natural diffusion of particles along their concentration gradient without the need for energy.