The cell membrane is the structure that regulates what enters and exits the cell and provides protection to organelles.

Here's why:

* Regulation of Entry and Exit: The cell membrane is selectively permeable, meaning it allows some substances to pass through while blocking others. This is crucial for maintaining the cell's internal environment and carrying out essential functions like nutrient uptake and waste removal.

* Protection of Organelles: The cell membrane acts as a barrier, separating the cell's internal components (organelles) from the external environment. It shields the organelles from harmful substances and maintains a stable internal environment.

Let me know if you want to know more about how the cell membrane works!