Oxygen levels in the photic zone fluctuate over the course of a 24-hr period. If you were measuring dissolved oxygen over the course of the day, when would you expect to see the lowest levels of oxygen and why?

A. Early evening -- when animals come to feed and disturb the surface waters.
B. Mid-afternoon -- because the activity of the Calvin cycle (the dark reactions) of photosynthesis are at their peak.
C. Early afternoon -- when the surface water warms up and sinks to the bottom.
D. Mid-morning -- because fish are most active and their respiration rates are highest.
E. During the night -- because the light reactions of photosynthesis are inactive.


Answer: E

Biology & Microbiology

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