A flask containing photosynthetic green algae and a control flask containing water with no algae are both placed under a bank of lights, which are set to cycle between 12 hours of light and 12 hours of dark. The dissolved oxygen concentrations in both flasks are monitored. Predict what the relative dissolved oxygen concentrations will be in the flask with algae compared to the control flask. The dissolved oxygen in the flask with algae will ________.
A) always be higher
B) always be lower
C) be higher in the light but the same in the dark
D) be higher in the light but lower in the dark
E) not be different from the control flask at any time

Question

Quizplus · Accepted Answer

Photosynthetic green algae produce oxygen during the light reactions of photosynthesis. Therefore, during the 12 hours of light, the dissolved oxygen in the flask with algae will be higher compared to the control flask. However, during the 12 hours of darkness, the algae will consume oxygen during cellular respiration, which will cause the dissolved oxygen concentration to decrease. As a result, the dissolved oxygen in the flask with algae will be higher in the light but lower in the dark compared to the control flask.

A Flask Containing Photosynthetic Green Algae and a Control Flask