Flagellar beat patterns and their possible evolution.

The roles of flagella and their functioning in unicellular organisms of various groups are described. Water propelled around a cell by the flagellum may cause locomotion of the cell and may bring near to the cell food particles that can be filtered from the water and phagocytosed. For purpose of locomotion alone, a relatively simple flagellar activity is adequate, but the efficient collection of particulate food requires modification of the flagellar activity or of the cell organization or both. The most sophisticated flagellar mechanisms are best explained as having been evolved for the collection of particulate food, although they may occur in groups that are now predominantly or entirely autotrophic. This is consistent with the view that heterotrophic flagellates requiring efficient particle collection for feeding evolved divergent flagellar mechanisms, based upon various structural patterns, and that only later did some of these divergent groups acquire their own particular types of plastid, presumably following phagotrophic uptake of the appropriate type of photosynthetic prokaryote and the establishment of a symbiotic association.