A flask containing photosynthetic green algae and a control flask containing water with no algae are both placed under a bank of lights that is 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

Question

Quizplus · Accepted Answer

During the light period, photosynthesis by the algae produces oxygen, increasing dissolved oxygen levels. In the dark, photosynthesis stops, and respiration by the algae consumes oxygen, potentially lowering dissolved oxygen levels compared to the control.

A Flask Containing Photosynthetic Green Algae and a Control Flask