Passive transport is a biological process that allows substances to move across cell membranes without the use of energy. This movement occurs along the concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration. Common examples of passive transport include diffusion, where molecules spread out evenly in a space, and osmosis, which specifically refers to the movement of water across a membrane. There are several types of passive transport, including facilitated diffusion, where specific proteins help transport molecules that cannot easily pass through the membrane. This process is essential for maintaining cellular functions and homeostasis, allowing cells to take in necessary nutrients and expel waste products efficiently.