Vacuole

A vacuole is a large, fluid-filled storage sac inside a cell. Many types of cells contain vacuoles, but they are most prominent in plant cells. A vacuole can store materials that a cell needs. It also provides the necessary internal pressure for a plant to remain erect and not wilt.

A vacuole is an organelle or a specialized structure inside a cell that has a particular function. Its main purpose involves storage and transport of materials inside a cell. Vacuoles in animal cells can store a variety of substances, including lipids (a kind of fat) and carbohydrates. In plants, vacuoles are very prominent, and when seen under a microscope they appear as large, round, clear structures. Vacuoles are filled with a watery fluid called cell sap (made up of water, salts, and sugar). In some plant cells, a vacuole may occupy as much as 90 percent of a cell's total volume. When a vacuole takes up this much space in a cell, it presses the cytoplasm (jelly-like fluid in a cell) against the cell wall, which eventually remains stretched out under this force. As long as the vacuole remains full, the plant maintains its turgor pressure (like the air pressing against the inside wall of a balloon). When the vacuole loses this fluid and decreases the pressure, it collapses temporarily and the plant wilts. Maintaining this cellular pressure is the prime responsibility of the vacuole in a mature plant. When pressure is maintained, the entire plant is able to keep its crisp shape. When it does not, the whole plant wilts.

[See alsoCell; Organelle; Plant Anatomy ]