A cell is a complex system. Like most systems, a cell contains a boundary that separates things that are inside the system from those that are outside of the system. Which part of the cell functions as a system boundary?

In plants, the cell boundary is the cell wall and the cell membrane. In animals, the boundary is the cell membrane and the cytoskeleton keeps the shape of the cell.

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.