vacuole

thumb|300x300px|Plant cell structure thumb|300x300px|Animal cell structure A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size; its structure varies according to the requirements of the cell.

==Discovery== Antonie van Leeuwenhoek described the plant vacuole in 1676. Contractile vacuoles ("stars") were first observed by Spallanzani (1776) in protozoa, although they were mistaken for respiratory organs. Dujardin (1841) named these "stars" as vacuoles. In 1842, Schleiden applied the term for plant cells, to distinguish the structure with cell sap from the rest of the protoplasm. In 1885, de Vries named the vacuole membrane as tonoplast. Christian de Duve discovered mammalian lysosomes using biochemical methods in the mid-1970s. De Duve named lysosomes based on their biochemical properties (from the Greek lysis – digestive and soma – body). Their physical form was confirmed shortly afterward by electron microscopy. Because the lysosome shares many properties with vacuoles across taxonomical kingdoms, the notion that vacuoles and lysosomes are distinctly different organelles is more historical than functional.