The organelle that helps keep the cell shape and determines what goes in and out of the cell is the cell membrane, also known as the plasma membrane.

Here's why:

* Shape: The cell membrane acts as a flexible barrier, providing structural support and maintaining the cell's shape.

* Selective Permeability: The cell membrane is selectively permeable, meaning it controls which substances can enter and exit the cell. This is crucial for maintaining the cell's internal environment and allowing for essential processes like nutrient uptake and waste removal.

While the cell wall in plant cells also provides structural support, it's not directly involved in regulating what enters and exits the cell.