Final answer:
The cell wall is the structure found outside the cell membrane of plant cells but not in animal cells.
Step-by-step explanation:
The structure found outside the cell membrane of plant cells that is not found in animal cells is the cell wall. The cell wall is a rigid layer located outside the cell membrane and provides structural support and protection to the plant cell. Animal cells do not have a cell wall, instead they have a flexible cell membrane that surrounds and protects the cell.
Learn more about Difference between plant and animal cells