Why is the plasma membrane called a selectively permeable membrane?

The plasma membrane is called a selectively permeable membrane because it selectively allows certain substances to pass through while restricting others. Here’s why:

1. Controlled Passage: It regulates the entry and exit of substances.
2. Selective Entry: Small, uncharged molecules can pass freely, while larger molecules or ions require specialized channels or transporters.
3. Protein Channels: Specific proteins in the membrane act as gateways, allowing only certain substances to pass based on size, charge, or recognition.
4. Regulation of Environment: It maintains the right balance of substances inside the cell and prevents the entry of harmful substances.
5. Homeostasis Maintenance: This selective permeability helps cells maintain a stable internal environment for optimal functioning.

Overall, the plasma membrane’s selective permeability is vital for controlling what enters and exits the cell, ensuring a suitable environment for cellular processes while safeguarding against harmful substances.