Tropism - wikipedia Tropism This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( September 2012 ) Phycomyces, a fungus, exhibiting phototropism A tropism ( from Greek τρόπος, tropos, `` a turning '' ) is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus ( as opposed to nastic movements which are non-directional responses ). Viruses and other pathogens also affect what is called `` host tropism '', `` tissue tropism '', or `` cell tropism '', or in which case tropism refers to the way in which different viruses / pathogens have evolved to preferentially target specific host species, specific tissue, or specific cell types within those species. Tropisms are usually named for the stimulus involved ( for example, a phototropism is a reaction to sunlight ) and may be either positive ( towards the stimulus ) or negative ( away from the stimulus ). Tropisms occur in four sequential steps. First, there is a perception to a stimulus, which is usually beneficiary to the plant. Next, signal transduction occurs. This leads to auxin redistribution at the cellular level and finally, the growth response occurs. Tropisms are typically associated with plants ( although not necessarily restricted to them ). Where an organism is capable of directed physical movement ( motility ), movement or activity in response to a specific stimulus is more likely to be regarded by behaviorists as a taxis ( directional response ) or a kinesis ( non-directional response ). In English, the word tropism is used to indicate an action done without cognitive thought : However, `` tropism '' in this sense has a proper, although non-scientific, meaning as an innate tendency, natural inclination, or propensity to act in a certain manner towards a certain stimulus. In botany, the Cholodny -- Went model, proposed in 1927, is an early model describing tropism in emerging shoots of monocotyledons, including the tendencies for the stalk to grow towards light ( phototropism ) and the roots to grow downward ( gravitropism ). In both cases the directional growth is considered to be due to asymmetrical distribution of auxin, a plant growth hormone. Contents 1 Types 2 See also 3 Notes 4 References 5 External links Types in plants ( and bacteria ) Example of gravitropism in the remains of a cellar of a Roman villa in the Archeologic Park in Baia, Italy Aerotropism, growth of plants towards or away from a source of oxygen Chemotropism, movement or growth in response to chemicals Electrotropism, movement or growth in response to an electric field Exotropism, continuation of growth `` outward, '' i.e. in the previously established direction Geotropism ( or gravitropism ), movement or growth in response to gravity Apogeotropism, negative geotropism Heliotropism, diurnal motion or seasonal motion of plant parts in response to the direction of the sun, ( e.g. the sunflower ) Apheliotropism, negative heliotropism Hydrotropism, movement or growth in response to water. In plants, the root cap senses differences in water moisture in the soil, and signals cellular changes that causes the root to curve towards the area of higher moisture. Prohydrotropism, positive hydrotropism Hygrotropism, movement or growth in response to moisture or humidity Magnetotropism, movement or growth in response to magnetic fields Orthotropism, movement or growth in the same line of action as the stimulus. Plagiotropism, movement or growth at an angle to a line of stimulus such as gravity or light. Phototropism, movement or growth in response to lights or colors of light Aphototropism, negative phototropism Skototropism, negative phototropism of vines Thermotropism, movement of growth in response to temperature Thigmotropism, movement or growth in response to touch or contact in viruses Amphotropism, wide host range ( e.g. infects many species or cell types ) Ecotropism, limited host range ( e.g. infects only one species or cell type ) HIV tropism, the means of entry into cells used by a given strain of HIV Neurotropism, a virus that preferentially infects the host 's nervous system. See also Chemotaxis Rapid plant movement Notes Jump up ^ For example, some cells may not be conducive for the growth of a virus, which determines its tropism. The stimulus of light on insects may also be seen as a type of ethological tropism. References Jump up ^ Haga, Ken ; Takano, Makoto ; Neumann, Ralf ; Iino, Moritoshi ( January 1, 2005 ). `` The Rice COLEOPTILE PHOTOTROPISM1 Gene Encoding an Ortholog of Arabidopsis NPH3 Is Required for Phototropism of Coleoptiles and Lateral Translocation of Auxin ( W ) ''. Plant Cell. doi : 10.1105 / tpc. 104.028357. Jump up ^ Cassab, Gladys I. ; Eapen, Delfeena ; Campos, María Eugenia ( 2013 - 01 - 01 ). `` Root hydrotropism : An update ''. American Journal of Botany. 100 ( 1 ) : 14 -- 24. doi : 10.3732 / ajb. 1200306. ISSN 0002 - 9122. PMID 23258371. External links Wikimedia Commons has media related to Tropism. Look up tropism in Wiktionary, the free dictionary. Plant movements Means Differential cell growth Changes in turgor pressure Tropisms ( directional ) Chemotropism Gravitropism Hydrotropism Heliotropism Phototropism Thermotropism Thigmotropism Nastic movements ( non-directional ) Nyctinasty Thigmonasty Retrieved from `` https://en.wikipedia.org/w/index.php?title=Tropism&oldid=823054405 '' Categories : Tropism Hidden categories : Articles needing additional references from September 2012 All articles needing additional references Talk Contents About Wikipedia Български Bosanski Català Čeština Cymraeg Deutsch Eesti Español Esperanto Euskara فارسی Français Gaeilge 한국어 Հայերեն Ido Bahasa Indonesia Italiano עברית Basa Jawa Қазақша Lietuvių Magyar മലയാളം မြန်မာဘာသာ Nederlands 日本 語 Polski Português Русский Srpskohrvatski / српскохрватски Svenska தமிழ் ไทย ᏣᎳᎩ Українська اردو Tiếng Việt 中文 31 more Edit links This page was last edited on 30 January 2018, at 00 : 36. About Wikipedia

Question: what is significance of tropic movement in plants
Answer: response to an environmental stimulus