It's important to note that not all cells have cell walls. Cell walls are found in:

* Plant cells: Made primarily of cellulose, they provide structural support and protection.

* Fungal cells: Composed of chitin, they also provide structural support.

* Bacterial cells: Made of peptidoglycan, they help maintain cell shape and protect against osmotic pressure.

Animal cells, however, do not have cell walls. They rely on a flexible cell membrane for structure and protection.