A scientist studying the oxygen concentration in sealed chambers containing cultured plant cells finds that when the chambers are illuminated, the concentration of oxygen increases. However, when the chambers are kept in the dark, the concentration of oxygen decreases. Why does the oxygen concentration decrease when the chamber is kept in the dark?

I believe the options are:

(A) Plant cell mitochondria consume oxygen by aerobic respiration.

(B) Plant cell chloroplasts run the photosynthetic pathways backward to consume oxygen.

(C) Plant cell chloroplasts switch their structure and function and become mitochondria.

(D) The chambers must not be properly sealed, so that oxygen is leaking out.

(E) The cultures in the chambers must be contaminated with some animal cells, since only animal cells consume oxygen.

The answer is (A) Plant cell mitochondria consume oxygen by aerobic respiration.

Explanation:

The presence of light triggers the process of photosynthesis and plants consume carbon dioxide and produce oxygen.

6CO2 + 6H20 + (energy) → C6H12O6 + 6O2

In the dark, the process of cellular respiration occurs which breaks down the glucose into ATP, water and oxygen. Since oxygen is the final electron acceptor in the electron transport chain, the plants consume oxygen and produce carbon dioxide.

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP