Vacuole

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Vacuole

A vacuole is a membrane

Membrane

A membrane is a layer of material which serves as a selective barrier between two Phase and remains permeation to specific particles or group of particles or substances when exposed to the action of a Membrane potential....
organelle

Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
which is present in all eukaryotic cells. Vacuoles are essentially enclosed compartments which are filled with fluid such as water or various enzymes, though in certain cases they may contain solids which have been engulfed.

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Encyclopedia

A vacuole is a membrane

Membrane

Organelle

Vesicle (biology)

A vesicle is a small bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell....
. The organelle has no basic shape or size, instead varying its structure according to the needs of the cell.

In general, vacuole functions include:

Isolating materials that might be harmful or a threat to the cell
Containing waste products
Maintaining internal hydrostatic pressure or turgor within the cell
Maintaining an acidic internal pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
Containing small molecules
Exporting unwanted substances from the cell

Vacuoles also play a major role in autophagy

Autophagy

In cell biology, autophagy, or autophagocytosis, is a catabolic process involving the degradation of a cell's own components through the lysosome machinery....
, maintaining a balance between biogenesis

Biogenesis

Biogenesis is the process of lifeforms producing other lifeforms, e.g. a spider lays eggs, which develop into spiders. It may also refer to biochemical processes of production in living organisms....
(production) and degradation (or turnover), of many substances and cell structures in certain organisms. Vacuoles store food and other materials needed by a cell. They also aid in destruction of invading bacteria

Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
or of misfolded proteins that have begun to build up within the cell. The function and importance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain protists than those of animals.

Plants

Most mature plant cell

Plant cell

Plant cells are eukaryote cells that differ in several key respects from the cell of other eukaryote organisms. Their distinctive features include:...
s have one or several vacuoles that typically occupy more than 30% of the cell's volume, and that can occupy as much as 90% of the volume for certain cell types and conditions. A vacuole is surrounded by a membrane called the tonoplast.

Transport of proton

Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s from cytosol to vacuole aids in keeping cytoplasmic pH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
stable, while making the vacuolar interior more acidic, allowing degradative enzymes to act. Although having a large central vacuole is the most common case, the size and number of vacuoles may vary in different tissues and stages of development. Cells of the vascular cambium

Vascular cambium

The vascular cambium is a lateral meristem in the vascular tissue of plants. The vascular cambium is the source of both the secondary xylem and the secondary phloem , and is located between these tissues in the stem and root....
, for example, have many small vacuoles in the winter, and one large one in the summer.

Aside from storage, the main role of the central vacuole is to maintain turgor pressure against the cell wall

Cell wall

A cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cell . It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism....
. Proteins found in the tonoplast control the flow of water into and out of the vacuole through active transport

Active transport

Active transport is the mediated process of moving particles across a biological membrane against a Concentration_gradient#In_biology . If the process uses chemical energy, such as from adenosine triphosphate , it is termed primary active transport....
, pumping potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
(K⁺) ion

Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s into and out of the vacuolar interior. Due to osmosis

Osmosis

Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....
, water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, the cell

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
will plasmolyse

Plasmolysis

Plasmolysis is the process in plant cells where the plasma membrane pulls away from the cell wall due to the loss of water through osmosis. The reverse process, deplasmolysis, can occur if the cell is in a Tonicity#Hypotonicity solution resulting in a higher external Osmotic_pressure and net flow of water into the cell....
. Turgor pressure exerted by vacuoles is also helpful for cellular elongation: as the cell wall is partially degraded by the action of auxins, the less rigid wall is expanded by the pressure coming from within the vacuole. Vacuoles can help some plant cells to reach considerable size. Another function of a central vacuole is that it pushes all contents of the cell's cytoplasm against the cellular membrane, and thus keeps the chloroplasts closer to light.

Animals

In animal cells, vacuoles perform mostly subordinate roles, assisting in larger processes of exocytosis

Exocytosis

Exocytosis is the durable process by which a cell directs the contents of secretory Vesicle_ out of the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane....
and endocytosis

Endocytosis

Endocytosis is the process by which cell s absorb material from outside the cell by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are large Chemical polarity molecules that cannot pass through the hydrophobic plasma membrane or cell membrane....
.

Exocytosis is the extrusion process of proteins and lipids from the cell. These materials are absorbed into secretory granules within the Golgi apparatus

Golgi apparatus

The Golgi apparatus is an organelle found in most eukaryote Cell . It was identified in 1898 by the Italian physician Camillo Golgi and was named after him....
before being transported to the cell wall and secreted into the extracellular environment. In this capacity, vacuoles are simply storage vesicles which allow for the containment, transport and disposal of selected proteins and lipids to the extracellular environment.

Endocytosis is the reverse of exocytosis and can occur in a variety of forms. Phagocytosis

Phagocytosis

File:Phagocytosis in three steps.pngPhagocytosis is the cell process of Phagocytes and Protists of engulfing solid particles by the cell membrane to form an internal phagosome, which is a food vacuole, or pteroid....
("cell eating") is the process by which bacteria, dead tissue, or other bits of material visible under the microscope are engulfed by cells. The material makes contact with the cell membrane, which then invaginates. The invagination

Invagination

Invagination means to fold inward or to sheath. In biology, this can refer to a number of processes.*Invagination is the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of Cell , the blastula, into a multi-layered organism,...
is pinched off, leaving the engulfed material in the membrane-enclosed vacuole and the cell membrane intact. Pinocytosis

Pinocytosis

In cellular biology, pinocytosis is a form of endocytosis in which small particles are brought into the cell suspended within small vesicle which subsequently fuse with lysosomes to hydrolyze, or to break down, the particles....
("cell drinking") is essentially the same process, the difference being that the substances ingested are in solution and not visible under the microscope. Phagocytosis and Pinocytosis are both undertaken in association with lysosomes which complete the breakdown of the material which has been engulfed.

Hydropic (vacuolar) changes are of importance in identifying various pathologies, such as the reversible cell swelling in renal tubules caused by hypoperfusion of the kidneys during open heart surgery

Open Heart Surgery

Open Heart Surgery was released on August 8, 2000 by rock band Virginwool. The band signed to Breaking/Atlantic Records after initially beginning signed to Universal Records....
.