Motility

Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals 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. 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, undulipodia (singular undulipodium) are slender cellular protuberances that project from the much larger cell body. Undulipodia, which consists of both eukaryotic flagella and eukaryotic cilia, may be motile or non-motile. Both motile cilia and flagella are motile. Primary cilia typically serve as sensory cellular organelles, 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 cells, propelled by the regular beat of their flagellum.
 * The bacterium E. coli, which swims by rotating a helical prokaryotic flagellum.
 * Non-motile examples includes Yersinia pestis @37 degrees C, Klebsiella pneumoniae, & Shigella.

Movements
Movements can be:
 * 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