central vacuole
/ SEN-trul VAK-yoo-ole /
If you have ever seen a wilted plant perk back up after watering, you have watched the central vacuole at work. It is a large, fluid-filled bag that takes up most of the inside of a mature plant cell — often more than 80 percent of the cell's volume — pushing everything else into a thin layer against the wall.
The central vacuole is a single large membrane-bound sac filled with a watery solution called cell sap. Its biggest structural job is to fill with water and press outward against the cell wall, creating an internal pressure called turgor that keeps non-woody plant tissue stiff and upright. Beyond support, the vacuole stores water, nutrients, ions, and waste products, isolates toxic compounds, and can hold pigments that color flowers and fruit; it even does some of the breakdown work that lysosomes handle in animals.
The central vacuole helps explain why plants droop when dry: lose the water, lose the pressure, and the leaves go limp. Although animal cells have small vacuoles too, the single dominating central vacuole is a hallmark of plant cells specifically, and is one of the standard features that distinguishes a plant cell from an animal cell.
A fresh stalk of celery snaps crisply because its cells are full of turgid central vacuoles; leave it out for a day to dry, and the same stalk bends like rubber.
Crispness in vegetables is turgor pressure from the central vacuole.
Turgor pressure is what supports soft plant tissue, not the cell wall alone; the wall resists the push, but the push itself comes from water in the vacuole.