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A vacuole (/ ˈ v æ k juː oʊ l /) is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. [ 1 ] [ 2 ] Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution , though in certain cases ...
The contractile vacuole is predominant in species that do not have a cell wall, but there are exceptions (notably Chlamydomonas) which do possess a cell wall. Through evolution , the contractile vacuole has typically been lost in multicellular organisms, but it still exists in the unicellular stage of several multicellular fungi , as well as in ...
The proportion of cell volume that is cytosol varies: for example while this compartment forms the bulk of cell structure in bacteria, [9] in plant cells the main compartment is the large central vacuole. [10] The cytosol consists mostly of water, dissolved ions, small molecules, and large water-soluble molecules (such as proteins).
Plant cells have a large central vacuole in the center of the cell that is used for osmotic control and nutrient storage. Contractile vacuoles are found in certain protists, especially those in Phylum Ciliophora. These vacuoles take water from the cytoplasm and excrete it from the cell to avoid bursting due to osmotic pressure.
Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of plant cells and fungal cells are usually larger than those of animal cells. Vacuoles of plant cells are surrounded by a membrane which transports ions against concentration gradients.
Some protists do not have cell walls and cannot experience turgor pressure. These few protists use their contractile vacuole to regulate the quantity of water within the cell. Protist cells avoid lysing in hypotonic solution by utilizing a vacuole which pumps water out of the cells to maintain osmotic equilibrium. [23]
The vacuolar form, which is most usually seen in laboratory cultures, has a large central vacuole surrounded by peripheral cytoplasm containing the nucleus and other organelles. [11] The granular form appears similar, but it has discrete granules within the central vacuole, which could represent metabolic products or reproductive elements. [ 12 ]
Organelles (literally "little organs") are usually membrane-bound structures inside the cell that have specific functions. Some major organelles that are suspended in the cytosol are the mitochondria , the endoplasmic reticulum , the Golgi apparatus , vacuoles , lysosomes , and in plant cells, chloroplasts .