Vacuole

A vacuole is a membrane-bound organelle found in many plant, fungal, and certain protist cells, and in some animal cells. It is bounded by a membrane called the tonoplast in plant cells and is formed by the fusion of vesicles from the endomembrane system. Vacuoles primarily function as storage compartments for water, ions, nutrients, pigments, and waste products, and they can play a role in maintaining cellular organization and pH balance.

In plant cells, the vacuole is often large and central, occupying a substantial portion of the cell’s interior. It helps maintain turgor pressure, which supports cell rigidity and overall plant structure. In animal cells, vacuoles are typically smaller and more transient, serving storage and transport roles. Some vacuoles contain hydrolytic enzymes and function similarly to lysosomes in digestion and waste processing.

Key functions include storage of water, ions, metabolites, and secondary compounds; osmoregulation and maintenance of cell volume; sequestration and detoxification of wastes; degradation of macromolecules through hydrolytic enzymes; sequestration of pigments and defense compounds; and involvement in autophagy and recycling processes.

Formation and structure: vacuoles originate from the endomembrane system and form by vesicle budding and fusion. The vacuolar membrane encloses the lumen and, in plants, is called the tonoplast. Central vacuoles in plants enlarge by uptake of water and solutes, while vacuoles in other cells adjust their size to meet cellular needs and may fuse with lysosome-like compartments.