Oxygen Evolution from Algae Illuminated by Short and Long Flashes of Light

The oxygen produced by illuminating Ankistrodesmus braunii with single light flashes has been determined using the Hersch galvanic oxygen cell. Measurements were made with the cells suspended in alkaline solution equilibrated with nitrogen containing oxygen at a partial pressure of 10−4 mm. Hg. A single light flash, if very brief (less than 5 millisec.) results in no measurable oxygen production; a longer flash (35 millisec.) gave a yield of approximately 1 mole O2/800 moles chlorophyll. A pair of flashes suitably spaced gave a greater yield than the sum of the yields when given individually, although one was so brief that by itself it produced no measurable oxygen. The yield of a long flash preceded by a short flash was twice as great as that of the long flash given alone; when the flash order was reversed the combined yield was smaller but still greater than for the long flash alone. The combined yield of a pair of flashes varies with the interval separating the flashes, rapidly rising to a maximum and then decaying more slowly. With a long and short flash the optimal interval was 0.7 sec. but some enhancement of yield was observed when the flashes were separated by as long as 10 or 15 sec. When the flashes were superimposed on background illumination the yields were increased and were measurable even for the short flashes. Measured with background illumination the optimal yield for a pair of short flashes was obtained with flashes separated by about 0.05 sec.