The outside covering that all plant cells have and not found in animal cells is called a cell wall.

Here's why:

* Structure: The cell wall is a rigid, protective layer that surrounds the cell membrane of plant cells. It is primarily composed of cellulose, a complex carbohydrate.

* Function: The cell wall provides structural support and protection for the plant cell. It also helps to regulate the movement of water and other substances into and out of the cell.

* Absence in animals: Animal cells lack cell walls. They have only a cell membrane, which provides flexibility and allows for movement.

Let me know if you'd like more information about plant cells or cell walls!