In biology, motility is the ability to move spontaneously and actively, consuming energy in the process. Motility is genetically determined (see genetic determinism) but may be affected by environmental factors. For instance, muscles give animals motility but the consumption of hydrogen cyanide (the environmental factor in this case) would adversely affect muscle physiology causing them to stiffen leading to rigor mortis. Most animals are motile but the term applies to unicellular and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in addition to animal locomotion. Motile marine animals are commonly called free-swimming.
Motility may also refer to an organism's ability to move food through its digestive tract, i.e., peristaltics (gut motility, intestinal motility, etc.). An example of intestinal motility is the contraction of smooth muscles in the gastrointestinal tract. This is referred to as the motility of the gastrointestinal tract and it serves two functions, which are to mix the luminal contents with various secretions and to move contents through the gastrointestinal tract from mouth to anus.
At the cellular level, different modes of motility exist:
Many cells are not motile, for example Klebsiella pneumoniae and Shigella, or under specific circumstances such as Yersinia pestis at 37 °C.
The events that are perceived as movements can be directed: