Passive transport is a biological process that allows substances to move across cell membranes without the need for energy. This movement occurs along a concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration. Common examples of passive transport include diffusion, osmosis, and facilitated diffusion. In passive transport, molecules such as oxygen and carbon dioxide can easily pass through the cell membrane. This process is essential for maintaining cellular functions, as it helps regulate the internal environment of cells and allows for the exchange of necessary substances with the surrounding environment.