Vacuoles are organelles of plant, fungal, and algal cells. They are part of the internal membrane system and are separated from the rest of the cytoplasm by a membrane called the tonoplast. A single large vacuole occupies more than 80 percent of the volume of most plant cells, mature fugal hyphae, and some algal cells. Many smaller vacuoles are found in expanding plant cells and in the tips of growing fungal hyphae. These vacuoles can be less than one micrometer in diameter. As the cell in which they reside matures, smaller vacuoles fuse to produce larger vacuoles.

Vacuoles are multifunctional organelles, and individual cells may contain more than one kind of vacuole, each kind having a different function. Vacuoles play crucial roles in cell expansion, serve as storage compartments for nutrients, and function as lytic organelles that contain digestive enzymes. Compounds contained within vacuoles also protect cells against environmental...