Answer;
Cell membrane
A cell membrane acts as a boundary that separates things that are inside the system from those that are outside the system.
Explanation;
It is a thin semipermeable structure that surrounds the cytoplasm of a cell.
The membrane functions to protect the integrity of the internal environment of the cell by allowing selective movements of materials in and out of the cell.
The membrane consists of a phospholipid bilayer with proteins embedded in it.
