No, plant cell walls are not mostly protein. They are primarily composed of cellulose, a complex carbohydrate.

Here's a breakdown of the main components of plant cell walls:

* Cellulose (40-50%): The most abundant component, providing structural support and rigidity.

* Hemicellulose (25-35%): A group of polysaccharides that bind to cellulose, providing additional strength and flexibility.

* Pectin (10-30%): A gel-like substance that helps bind cells together and creates the middle lamella, a layer between cell walls.

* Lignin (10-25%): A complex polymer that adds strength and rigidity to the cell wall, particularly in woody tissues.

* Proteins (5-10%): While present, they are a minor component compared to carbohydrates and are involved in various functions like cell wall formation, enzyme activity, and signaling.

So, while proteins play a role in the plant cell wall, they are not the dominant component.