Here's why:
* Diffusion: The movement of molecules from an area of high concentration to an area of low concentration. The cell membrane acts as a barrier, but it's selectively permeable, meaning it allows some molecules to pass through while blocking others.
* Osmosis: The movement of water molecules across a semipermeable membrane from an area of high water concentration to an area of low water concentration. The cell membrane acts as the semipermeable membrane in this process.
* Active Transport: The movement of molecules against their concentration gradient (from low to high concentration), requiring energy. The cell membrane contains proteins that actively pump molecules across the membrane, utilizing energy from ATP.
Therefore, the cell membrane is crucial for all three processes, regulating the movement of molecules in and out of the cell.
