In plant cells, what substance primarily makes up the cell wall?

In plant cells, the cell wall is primarily made up of cellulose. Cellulose is a complex carbohydrate that forms the structural component of the cell wall, providing rigidity and strength to the plant. This allows plants to maintain their shape and supports the overall structure of the plant as it grows. The arrangement of cellulose fibers in the cell wall also plays a crucial role in allowing water and nutrients to pass through while protecting the plant from pathogens.

Other substances mentioned, like lignin, are present in some cell walls, especially in woody plants, but are not the primary component. Lignin adds strength and rigidity to certain types of plant cells, particularly in vascular tissues, but it is not the main constituent of all plant cell walls. Similarly, chitin is found in the exoskeletons of arthropods and in the cell walls of fungi, not in plant cells. Lastly, proteins can be associated with the cell wall, but they do not make up the structural framework in the same way that cellulose does. Thus, cellulose is the key component that defines the structure and function of the plant cell wall.