Base your answer on the information below and on your knowledge of biology. A small green plant was placed in a flask as shown below. A sensor that measures the CO2 content of the air in the flask was inserted, and then the flask was sealed with a rubber stopper. The other end of the sensor was connected to a computer to monitor and record CO2 levels in the flask over a period of time.

For part of the time the flask was placed in bright light and for part of the time it was placed in total darkness. The graph below shows data that were recorded by the sensor over a period of time.

Which process most likely caused the change in CO2 level in the flask over the last 37 minutes?