It's not a single part of the plant cell that prevents substances from going in and out. Instead, it's the cell membrane that controls the movement of substances into and out of the cell.

Here's why:

* Selective Permeability: The cell membrane is selectively permeable, meaning it allows some substances to pass through while blocking others. This control is essential for maintaining the cell's internal environment and carrying out its functions.

* Structure: The cell membrane is made up of a phospholipid bilayer with embedded proteins. This structure helps regulate the movement of various molecules.

While the cell wall provides structural support and protection, it's primarily a rigid barrier that doesn't actively control the passage of substances like the cell membrane does.