A flask containing photosynthetic green algae and a control flask containing only water are exposed to a cycle of 12 hours of light and 12 hours of darkness. Which of the following statements best describes how the relative dissolved oxygen concentration in the flask with algae will compare to the control flask?
A) It will always be higher in the control.
B) It will always be lower in the control.
C) It will be lower in the control in the light, but the same in the dark.
D) It will be lower in the control in the light, but higher in the control in the dark.

Question

Quizplus · Accepted Answer

During the light periods, photosynthesis in the algae produces oxygen, increasing its concentration in the flask with algae compared to the control. In the dark, photosynthesis stops but respiration continues, consuming oxygen and potentially lowering its concentration in the algae flask below that of the control.

A Flask Containing Photosynthetic Green Algae and a Control Flask