Vacuole Guide, Meaning , Facts, Information and Description
Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting unwanted substances from the cell, or even determining relative cell size. The cavity that is the vacuole is considered nonprotoplasmic and the contents classified as ergastic according to some authors (Esau, 1965). Vacuoles are especially conspicuous in most plant cells.Vacuoles are typically filled with a liquid called cell sap, the composition of which can vary (even between vacuoles in the same cell), but is principally water. Water tends to move along concentration gradients into vacuoles.
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Vacuoles have the following functions:
A contractile vacuole is used to pump excess water out of the cell to reduce osmotic pressure and keep the cell from bursting. Contractile vacuoles are found in some freshwater protozoa.
Vacuole functions
Examples of vacuoles that perform each of these functions are described below.Vacuoles in protists
Some protists and macrophages use food vacuoles in phagocytosis—the intake of large molecules, particles, or even other cells, by the cell for digestion.Vacuoles in plant cells
Most mature plant cells have a central vacuole, which often takes up more than 90% of the cell interior. It is surrounded by a membrane and is called the tonoplast. The tonoplast actually serves several different purposes:
The tonoplast stores water, with the primary purpose of regulating turgor pressure. The cell controls the flow of water into and out of the tonoplast by using active transport to pump ions of potassium (K+) into and out of the interior liquid. Because of osmosis, wherever solutes go, water follows.Vacuoles in budding yeast cells
In budding yeast cells, vacuoles are the storage compartments of amino acids and the detoxification compartment, which are described in previous topics. Recently, vacuoles of budding yeast cells have been studied. As a result, another function of vacuoles was discovered. Under conditions of starvation, proteins are degraded in vacuoles; this is called autophagy. First, cytoplasms, mitochondria, and small organelles are covered with multiplex plasma membranes called autophagosomes. Next, the autophagosomes fuse the vacuoles. Finally, the cytoplasms and the organelles are degraded.
In a vacuole of budding yeast, a black particle sometimes appears. It is called a dancing body. The dancing body moves actively in the vacuole and appears and disappears within 10 minutes to several hours. In previous research, it was suggested but not proven that the main component of the dancing body is polyphosphate acid. But the main component has been determined to be crystallized sodium polyphosphate and its function has been studied. It is thought that its function is to supply and store phosphates in budding yeast cells.