Motility Explained

Motility should not be confused with Motility (album).

Motility is the ability of an organism to move independently using metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components.

Motility is observed in animals, microorganisms, and even some plant structures, playing crucial roles in activities such as foraging, reproduction, and cellular functions. It is genetically determined but can be influenced by environmental factors.

In multicellular organisms, motility is facilitated by systems like the nervous and musculoskeletal systems, while at the cellular level, it involves mechanisms such as amoeboid movement and flagellar propulsion. These cellular movements can be directed by external stimuli, a phenomenon known as taxis. Examples include chemotaxis (movement along chemical gradients) and phototaxis (movement in response to light).

Motility also includes physiological processes like gastrointestinal movements and peristalsis. Understanding motility is important in biology, medicine, and ecology, as it impacts processes ranging from bacterial behavior to ecosystem dynamics.

Definitions

Motility, the ability of an organism to move independently, using metabolic energy,^{[1] [2]} can be contrasted with sessility, the state of organisms that do not possess a means of self-locomotion and are normally immobile. Motility differs from mobility, the ability of an object to be moved.

The term vagility encompasses both motility and mobility; sessile organisms including plants and fungi often have vagile parts such as fruits, seeds, or spores which may be dispersed by other agents such as wind, water, or other organisms.^[3]

Motility is genetically determined,^[4] but may be affected by environmental factors such as toxins. The nervous system and musculoskeletal system provide the majority of mammalian motility.^{[5] [6] [7]}

In addition to animal locomotion, most animals are motile, though some are vagile, described as having passive locomotion. Many bacteria and other microorganisms, including even some viruses,^[8] and multicellular organisms are motile; some mechanisms of fluid flow in multicellular organs and tissue are also considered instances of motility, as with gastrointestinal motility. Motile marine animals are commonly called free-swimming,^{[9] [10] [11]} and motile non-parasitic organisms are called free-living.^[12]

Motility includes an organism's ability to move food through its digestive tract. There are two types of intestinal motility – peristalsis and segmentation. This motility is brought about by the contraction of smooth muscles in the gastrointestinal tract which mix the luminal contents with various secretions (segmentation) and move contents through the digestive tract from the mouth to the anus (peristalsis).^[13]

Cellular level

See also: Cell migration.

At the cellular level, different modes of movement exist:

• amoeboid movement, a crawling-like movement, which also makes swimming possible^{[14] [15]}
• filopodia, enabling movement of the axonal growth cone^[16]
• flagellar motility, a swimming-like motion (observed for example in spermatozoa, propelled by the regular beat of their flagellum, or the E. coli bacterium, which swims by rotating a helical prokaryotic flagellum)
• gliding motility
• swarming motility
• twitching motility, a form of motility used by bacteria to crawl over surfaces using grappling hook-like filaments called type IV pili.

Many cells are not motile, for example Klebsiella pneumoniae and Shigella, or under specific circumstances such as Yersinia pestis at 37 °C.

Movements

See also: Taxis.

Events perceived as movements can be directed:

• along a chemical gradient (see chemotaxis)
• along a temperature gradient (see thermotaxis)
• along a light gradient (see phototaxis)
• along a magnetic field line (see magnetotaxis)
• along an electric field (see galvanotaxis)
• along the direction of the gravitational force (see gravitaxis)
• along a rigidity gradient (see durotaxis)
• along a gradient of cell adhesion sites (see haptotaxis)
• along other cells or biopolymers

See also

• Cell migration

Notes and References

1. Web site: Motility . 10 March 2018.
2. Web site: Online Etymology Dictionary . "capacity of movement," 1827, from French motilité (1827), from Latin mot-, stem of movere "to move" (see move (v.))..
3. Web site: Botanical Nerd Word: Vagile . torontobotanicalgarden.ca/ . 7 November 2016 . 29 September 2020.
4. Book: Nüsslein-Volhard, Christiane . Coming to life: how genes drive development . 2006 . Kales Press . San Diego, California . 978-0979845604 . 75 . https://books.google.com/books?id=n19wkrmFJhwC&pg=PA73 . 6 Form and Form Changes . During development, any change in cell shape is preceded by a change in gene activity. The cell's origin and environment that determine which transcription factors are active within a cell, and, hence, which genes are turned on, and which proteins are produced..
5. Book: Fullick, Ann . Edexcel A2-level biology . 2009 . Pearson . Harlow . 978-1-4082-0602-7 . 138 . 7.1.
6. Book: Fullick . Ann . Edexcel A2-level biology . 2009 . Pearson . Harlow . 978-1-4082-0602-7 . 67 . 6.1 .
7. E. Cooper . Chris . C. Brown . Guy . The inhibition of mitochondrial cytochrome oxidase by the gases carbon monoxide, nitric oxide, hydrogen cyanide and hydrogen sulfide: chemical mechanism and physiological significance . Journal of Bioenergetics and Biomembranes . October 2008 . 40 . 5 . 533–539 . 10.1007/s10863-008-9166-6 . 18839291 . 13682333.
8. P.H. Hamming . N.J. Overeem. J. Huskens. Influenza as a molecular walker . Chemical Science . November 2019 . 11 . 1. 27-36 . 10.1039/C9SC05149J. 7021193 .
9. Krohn . Martha M. . Boisdair . Daniel . Use of a Stereo-video System to Estimate the Energy Expenditure of Free-swimming Fish . Canadian Journal of Fisheries and Aquatic Sciences . May 1994 . 51 . 5 . 1119–1127 . 10.1139/f94-111.
10. Cooke . Steven J. . Thorstad . Eva B. . Hinch . Scott G. . Activity and energetics of free-swimming fish: insights from electromyogram telemetry . Fish and Fisheries . March 2004 . 5 . 1 . 21–52 . 10.1111/j.1467-2960.2004.00136.x . 2004AqFF....5...21C . We encourage the continued development and refinement of devices for monitoring the activity and energetics of free-swimming fish.
11. Carey . Francis G. . Lawson . Kenneth D. . Temperature regulation in free-swimming bluefin tuna . Comparative Biochemistry and Physiology A . February 1973 . 44 . 2 . 375–392 . 10.1016/0300-9629(73)90490-8 . Acoustic telemetry was used to monitor ambient water temperature and tissue temperature in free-swimming bluefin tuna (Thunnus thynnus Linneaus, 1758) over periods ranging from a few hours to several days. . 4145757.
12. Web site: About Parasites . Centers for Disease Control . 29 September 2020 . Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature..
13. Book: Vander's Human Physiology: The Mechanisms of Body Function (14th ed). . Wildmarier, Eric P. . Raff, Hershel . Strang, Kevin T. . McGraw Hill . 2016 . New York, NY . 528 .
14. 10.1371/journal.pone.0027532 . 22096590 . 3212573 . Amoeboid Cells Use Protrusions for Walking, Gliding and Swimming . PLOS ONE . 6 . 11 . e27532 . 2011 . Van Haastert . Peter J. M. . 2011PLoSO...627532V . free .
15. 10.1073/pnas.1011900107 . 20921382 . 2973909 . On the swimming of Dictyostelium amoebae . Proceedings of the National Academy of Sciences . 107 . 44 . E165–6 . 2010 . Bae . A. J. . Bodenschatz . E. . 2010PNAS..107E.165B . 1008.3709 . free .
16. Book: Gilbert . Scott . Developmental biology . 2006 . Sinauer Associates, Inc. Publishers . Sunderland, Mass. . 9780878932504 . 395 . 8th..