FIG. 3.

Influence of 2 h–2 h dark-light cycles on gravitactic orientation (r value) and swimming speed of Euglena gracilis, as well as the oxygen concentration in a closed bioreactor. Cells were measured every 30 min. The bars indicate the light period. The figure shows representative dark-light cycles with subsequent constant illumination. The r value is a parameter of the precision of the movement direction (0: no orientation, 1: all cells swim in the same direction). Open circles: precision of orientation. Triangles: motile cells (%). Crosses: oxygen concentration. For details, see the text.