Here's why:
* The cell membrane is selectively permeable: This means it allows some substances to pass through while blocking others. This selectivity is crucial for maintaining the cell's internal environment.
* Passive transport: Substances like water, oxygen, and carbon dioxide can move across the membrane passively, meaning they don't require energy from the cell. This is driven by concentration gradients or pressure differences.
* Active transport: For other substances, like nutrients and waste products, the cell uses energy to move them across the membrane against their concentration gradients. This is called active transport.
So, the cell membrane acts like a gatekeeper, controlling the movement of materials in and out of the cell, ensuring its survival and proper functioning.
