So far, we have only discussed rhythms for multi-cellular organisms. Do
individual cells have rhythms? Yes!! In the 1950's, Beatrice
Sweeney, a pioneering plant clock biologist, was able to measure
rhythms of oxygen release in individual Gonyaulax (an alga) cells.
Gonyaulax also exhibits a rhythm of luminescence. Various
rhythms have been detected and studied in other single-celled organisms
such as Paramecium, Euglena, Acetabularia,
(see Activity section).
In multi-cellular organisms, scientists often study the rhythms of
individual cells. In the sea hare, Aplysia californica , optic nerves
in eyes removed form the animals exhibit circadian activity rhythms.
Cells from a variety of organisms are being studied with respect to
rhythms in ion exchange, hormone release, and genetic activity.