Motility is a biological
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in addition to animal locomotion
Animal locomotion
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...

. Motile marine animals are commonly called free-swimming.

The opposite of motility is sessility
Sessility (zoology)
In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...


Motility may also refer to an organism's ability to move food through its digestive tract, i.e., peristaltics (gut motility, intestinal motility, etc.).

Cellular-level motility

At the cellular level, undulipodia (singular undulipodium) are slender cellular
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 bilayer....

 protuberances that project from the much larger cell body
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

. Undulipodia, which consists of both eukaryotic
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 flagella and eukaryotic cilia,
may be motile or non-motile. Both motile cilia and flagella are motile. Primary cilia typically serve as sensory cellular 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 bilayer....

s, and are non-motile. Eukaryotic cilia are structurally identical to eukaryotic flagella, although distinctions are sometimes made according to function and/or length.

Examples of single-cellular motility

  • Sperm
    The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

     cells, propelled by the regular beat of their flagellum
    A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

  • The bacterium E. coli, which swims by rotating a helical prokaryotic flagellum.
  • Non-motile examples includes Yersinia pestis
    Yersinia pestis
    Yersinia pestis is a Gram-negative rod-shaped bacterium. It is a facultative anaerobe that can infect humans and other animals....

    @37 degrees C, Klebsiella pneumoniae
    Klebsiella pneumoniae
    Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose fermenting, facultative anaerobic, rod shaped bacterium found in the normal flora of the mouth, skin, and intestines....

    , & Shigella
    Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...



Movements can be:
  • along a chemical gradient (see chemotaxis
    Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...

  • along a temperature gradient (see thermotaxis
    Thermotaxis is a behavior in which an organism directs its locomotion up or down a gradient of temperature.Lab research has determined that some slime molds and small nematodes can migrate along amazingly shallow temperature gradients of less than 0.1C/cm...

  • along a light gradient (see phototaxis
    Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves in response to the stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis...

  • along a magnetic field line (see magnetotaxis
    Logically, magnetotaxis describes an ability to sense a magnetic field and coordinate movement in response. It was applied to the behavior of certain motile, aquatic bacteria in 1975 by R. P. Blakemore....

  • 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
    Haptotaxis is the directional motility or outgrowth of cells, e.g. in the case of axonal outgrowth, usually up a gradient of cellular adhesion sites or substrate-bound chemoattractants...

  • along other cells or biopolymer
    Biopolymers are polymers produced by living organisms. Since they are polymers, Biopolymers contain monomeric units that are covalently bonded to form larger structures. There are three main classes of biopolymers based on the differing monomeric units used and the structure of the biopolymer formed...

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