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A vacuole is a cell organelle found in a number of different cell types. Vacuoles are fluid-filled, enclosed structures that are separated from the cytoplasm by a single membrane. They are found mostly in plant cells and fungi. However, some protists, animal cells, and bacteria also contain vacuoles. Vacuoles are responsible for a wide variety of important functions in a cell including nutrient storage, detoxification, and waste exportation.
Plant Cell Vacuole
Mariana Ruiz LadyofHats/Wikimedia Commons
A plant cell vacuole is surrounded by a single membrane called the tonoplast. Vacuoles are formed when vesicles, released by the endoplasmic reticulum and Golgi complex, merge together. Newly developing plant cells typically contain a number of smaller vacuoles. As the cell matures, a large central vacuole forms from the fusion of smaller vacuoles. The central vacuole can occupy up to 90% of the cell's volume.
Plant cell vacuoles perform a number of functions in a cell including:
- Turgor pressure control - turgor pressure is the force exerted against the cell wall as the contents of the cell push the plasma membrane against the cell wall. The water filled central vacuole exerts pressure on the cell wall to help plant structures remain rigid and erect.
- Growth - the central vacuole aids in cell elongation by absorbing water and exerting turgor pressure on the cell wall. This growth is aided by the release of certain proteins that reduce cell wall rigidity.
- Storage - vacuoles store important minerals, water, nutrients, ions, waste products, small molecules, enzymes, and plant pigments.
- Molecule degradation - the internal acidic environment of a vacuole aids in the degradation of larger molecules sent to the vacuole for destruction. The tonoplast helps to create this acidic environment by transporting hydrogen ions from the cytoplasm into the vacuole. The low pH environment activates enzymes, which degrade biological polymers.
- Detoxification - vacuoles remove potentially toxic substances from the cytosol, such as excess heavy metals and herbicides.
- Protection - some vacuoles store and release chemicals that are poisonous or taste bad to deter predators from consuming the plant.
- Seed germination - vacuoles are a source of nutrients for seeds during germination. They store the necessary carbohydrates, proteins, and fats needed for growth.
Plant vacuoles function similarly in plants as lysosomes in animal cells. Lysosomes are membranous sacs of enzymes that digest cellular macromolecules. Vacuoles and lysosomes also participate in programmed cell death. Programmed cell death in plants occurs by a process called autolysis (auto-lysis). Plant autolysis is a naturally occurring process in which a plant cell is destroyed by its own enzymes. In an ordered series of events, the vacuole tonoplast ruptures releasing its contents into the cell cytoplasm. Digestive enzymes from the vacuole then degrade the entire cell.
Plant Cell: Structures and Organelles
To learn more about organelles that can be found in typical plant cells, see:
- Cell (Plasma) Membrane - surrounds the cytoplasm of a cell, enclosing its contents.
- Cell Wall - outer covering of the cell that protects the plant cell and gives it shape.
- Centrioles - organize the assembly of microtubules during cell division.
- Chloroplasts - the sites of photosynthesis in a plant cell.
- Cytoplasm - gel-like substance within the cell membrane composed.
- Cytoskeleton - a network of fibers throughout the cytoplasm.
- Endoplasmic Reticulum - extensive network of membranes composed of both regions with ribosomes (rough ER) and regions without ribosomes (smooth ER).
- Golgi Complex - responsible for manufacturing, storing and shipping certain cellular products.
- Lysosomes - sacs of enzymes that digest cellular macromolecules.
- Microtubules - hollow rods that function primarily to help support and shape the cell.
- Mitochondria - generate energy for the cell through respiration.
- Nucleus - membrane bound structure that contains the cell's hereditary information.
- Nucleolus - structure within the nucleus that helps in the synthesis of ribosomes.
- Nucleopore - tiny hole within the nuclear membrane that allows nucleic acids and proteins to move into and out of the nucleus.
- Peroxisomes - tiny structures bound by a single membrane that contain enzymes that produce hydrogen peroxide as a by-product.
- Plasmodesmata - pores or channels between plant cell walls that allow molecules and communication signals to pass between individual plant cells.
- Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly.
- Vacuole - typically large structure in a plant cell that provides support and participates in a variety of cellular functions including storage, detoxification, protection, and growth.