Cell walls revised.

Plant cells have a cell wall, large central vacuole, and plasmodesmata. Like other eukaryotes, plants have a nucleus, plasma membrane, mitochondria, and other organelles, but plant cells differ from animal, fungal, and protist cells in a number of important ways. The most obvious difference is the presence of a cell wall which surrounds each cell. It is composed primarily of cellulose, a complex carbohydrate made from glucose. Cellulose provides structural support while remaining flexible; flower …

…into the cell, increasing its volume. Because of the cell wall, however, the amount of space into which the cell can expand is limited. The cell thus exerts outward pressure on its cell wall, and when all cells are maintaining this pressure, the plant gains rigidity. You can notice this by comparing crisp fresh celery with celery that has sat around and grown limp. The old celery has lost fluids, and is no longer rigid.