Here's why:

* Cell membrane: The cell membrane acts as a barrier, controlling what enters and leaves the cell. It's essential for maintaining the cell's internal environment.

* Nuclear envelope: The nuclear envelope acts as a barrier, controlling what enters and leaves the nucleus. It's essential for protecting the genetic material within the nucleus.

Both the cell membrane and the nuclear envelope are selectively permeable membranes that regulate the passage of molecules in and out of their respective compartments.