Motility

In biology, motility is the ability to move spontaneously and actively, consuming energy in the process. 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.

The opposite of motility is sessility.

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, different modes of motility exist:
 * flagellar motility, a swimming-like motion (observed for example in spermatozoa, propelled by the regular beat of their flagellum, or E. coli, which swims by rotating a helical prokaryotic flagellum)
 * amoeboid movement, a crawling-like movement, which also makes swimming possible
 * gliding motility
 * Swarming motility

Many cells are not motile, for example Yersinia pestis at 37 °C, Klebsiella pneumoniae and Shigella.

Movements
The events that are 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