Nonmotile

Nonmotile refers to the absence of self-directed movement. In biology, motility is the capability of an organism, cell, or particle to move on its own, using structures such as flagella or cilia, or by amoeboid movement. Nonmotile is therefore used to describe organisms or cells that lack these propulsion mechanisms or that do not actively move under normal conditions.

Nonmotility may be intrinsic (a structural or genetic absence of motility apparatus) or conditional (movement is inhibited by environment or life stage). Some nonmotile cells can still be displaced by external forces, such as fluid flow, mechanical contact, or host movement; this does not constitute autonomous motility.

Examples occur across biology. Many bacteria are nonmotile because they lack flagella; others are motile. In humans, red blood cells are nonmotile in circulation, and many cells possess nonmotile primary cilia that function as sensory organelles. In plants, individual cells and tissues are largely nonmotile, and movement is typically limited to growth responses rather than self-propelled locomotion. Viruses are generally considered nonmotile, lacking independent machinery for movement and relying on external agents for transmission.

Understanding motility and nonmotility has applications in taxonomy, pathogenesis, and medicine. Motility assays help identify bacterial species, and defects in motility-related organelles can underlie human disorders such as immotile cilia syndromes. The concept also informs discussions of how organisms interact with their environments and how dispersal occurs.