Membrane transport refers to the movement of substances across a cell's plasma membrane. This process is essential for maintaining the cell's internal environment and involves various mechanisms, including diffusion, osmosis, and active transport. These mechanisms allow nutrients, ions, and waste products to enter or exit the cell as needed. There are two main types of membrane transport: passive and active. Passive transport does not require energy and occurs when substances move along their concentration gradient, while active transport requires energy to move substances against their gradient. Both types are crucial for cellular function and homeostasis.