Basics of Vacuoles Vacuoles are: relatively large, membrane-bound organelles not a distinct shape but rather appear as expandable sacs that are often filled with water, organic and inorganic material primarily found in plant and fungi cells, occasionally in protist and bacterial cells, but never in animal cells generally used for structural support, waste removal and storage, but can have distinctive functions for certain cells both structure and function can vary between different vacuoles, even between two in the same cell
General Structure – Plants and Fungi Plant and fungi cells have one large, central vacuole, which can take up as much as 80% of the space in the cell. This vacuole is made up of: Tonoplast, the membrane which encloses the vacuole Cell sap, the liquid that fills the vacuole instead of protoplasm Because it is enclosed by a membrane, the vacuole is part of the endomembrane system. Essentially, this means that it is part of a group of organelles made from membranes, connected by the cytoplasmic network.
Vacuoles in Animals? Vacuoles are only found in plant cells, fungi cells and some protist and bacteria cells, NOT in animal cells. Animal cells DO have similar organelles, known as vesicles. Vesicles are generally much smaller than vacuoles but much more abundant. Whereas plant and fungi cells often only have one, animal cells can have many. Vesicles can have slightly different functions than vacuoles and are also used for transporting material from one part of the cell to another. In lower-level sources, the two terms, vesicle and vacuole, are sometimes combined under the term “vacuole”. This is technically incorrect but more a matter of terminology than concept.
General Functions in Cells Though specific function varies between different vacuoles, the majority of vacuoles share the following functions: Containment – storing, decomposing or removing unwanted substances from the cell’s interior Protection – storing and isolating dangerous substances, toxic to the cell’s health Defense – storing chemicals to be used against invading bacteria Autophagy – breaking down and decomposing old cell parts at a rate that balances out the production of cell organelles Homeostasis – maintaining an acidic internal pH, turgor pressure and fluid balance
Specific Functions – Plants and Fungi In addition to the general functions, in plant and fungi cells, where vacuoles play major roles, vacuoles may also have the following functions: Growth and Development – storing salts, minerals, nutrients, and proteins that assist in plant growth Attraction – storing pigment that provides the plant and its flowers their color, allowing them to attract insects for pollination Defense – releasing poisonous or irritating molecules and chemicals that discourage predators from consuming the plant Structure – exerting pressure against the plant’s cell walls, enabling the cell to maintain its form
Glossary Cell Sap – the liquid enclosed in the vacuole (as opposed to cytoplasm); is composed primarily of water, but exact composition can vary from cell to cell. Tonoplast – literally meaning stretching, it is the cytoplasmic membranes of vacuoles Turgor Pressure - the pressure the vacuole exerts on a plant or fungi cell’s wall, which is determined by the volume of water in the vacuole Vesicles – similar to vacuoles but are smaller and have some different functions; they are found in animal cells