Here's why:
* Cell membranes are selectively permeable: They allow some substances to pass through easily, while others require assistance.
* Transport proteins act as "gates" or "carriers": They bind to specific molecules and help them move across the membrane. There are two main types:
* Channel proteins: Form pores or channels through the membrane, allowing certain molecules to pass through passively (e.g., water, small ions).
* Carrier proteins: Bind to molecules and change shape, transporting them across the membrane. This can be active transport (requiring energy) or facilitated diffusion (passive).
Let me know if you'd like to know more about specific types of transport proteins!
