What is the primary difference between active and passive transport?

The primary difference between active and passive transport lies in the requirement of energy. In active transport, cells move substances against their concentration gradient, which means they are moving from an area of lower concentration to an area of higher concentration. This process necessitates the expenditure of energy, often in the form of ATP (adenosine triphosphate). This energy is essential for transporting molecules that cannot freely diffuse across the cell membrane due to size, charge, or polarity.

On the other hand, passive transport involves the movement of substances across a membrane without the use of energy. This occurs along the concentration gradient, from areas of higher concentration to areas of lower concentration, until equilibrium is reached. This process relies on natural diffusion and involves mechanisms like simple diffusion, facilitated diffusion, or osmosis.

Understanding this fundamental distinction helps clarify cellular transport mechanisms, highlighting how active transport is crucial for maintaining specific concentrations of ions and molecules within the cell that are vital for various cellular functions.