In cell biology, a biased random walk enables bacteria to source for food and flee from harm. Bacteria propell themself with the aid of flagella in a process called chemotaxis, and a typical bacteria trajectory has many charactistics of a random walk. They move forward for a certain distance, then the course is abrubtly altered by a process called tumbling. The average change of direction is about 60°. Cell biology (also called cellular biology or cytology, from the Greek kytos, container) is an academic discipline which studies cells. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria is also the fictional name of a warring nation under Benzino Napaloni as dictator, in the 1940 film The Great Dictator... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Chemotaxis is the phenomenon in which bodily cells, bacteria, and other single-celled or multicellular organisms direct their movements according to certain chemicals in their environment. ... In mathematics and physics, a random walk is a formalization of the intuitive idea of taking successive steps, each in a random direction. ...
The presence of a food supply gradient adds bias to the random walk and hence the phrase biased random walk. When the bacterium moves away from a attractant like a food source (sugar) the tumbling frequency increases (tumbling, negative chemotaxis). This makes it possible for the bacterium to change course and head back to the food source. The bacterium is also able to steer away from a repellant such as a toxin by reducing the tumbling frequency (running, positive chemotaxis). The bacterium is able to detect a chemical gradient not by monitoring a difference in concentration in head and tail but rather by a temporal sensing mechanism keeping track of concentration through time and space. The biased random walk in bacterium motility may be applied in robotic sensors that are able to find the source of an oil spill in oceans. In vector calculus, the gradient of a scalar field is a vector field which points in the direction of the greatest rate of change of the scalar field, and whose magnitude is the greatest rate of change. ... Bias has several different meanings, most relating to an offset or prejudice of some sort. ... Motility is the ability to move spontaneously and independently. ... A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition. ...
In physics, randomwalks are used as simplified models of physical Brownian motion and the random movement of molecules in liquids and gases.
Randomwalk can be used to sample from a state space which is unknown or very large, for example to pick a random page off the internet or, for research of working conditions, a random illegal worker in a given country.
The overall movement of a bacterium is the result of alternating tumble and swim phases.
If one watches a bacterium swimming in a uniform environment, its movement will look like a randomwalk with relatively straight swims interrupted by random tumbles that reorient the bacterium.
It remains remarkable that this purposeful randomwalk is a result of simply choosing between two methods of random movement, namely tumbling and straight swimming.
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