Why does the amount of carbon dioxide decrease from 7:00 AM until 7:00 PM and then start increasing?
During daylight hours, photosynthesis, but not respiration, occurs in the plant. When light decreases, photosynthesis stops and cellular respiration start.
The plant only performs metabolic processes, including photosynthesis and respiration, during the day.
The rate of photosynthesis remains constant throughout the time period, but respiration occurs only overnight.
When light is available, the plant's rate of photosynthesis exceeds the rate of respiration. When light decreases, the rate of respiration exceeds the rate of photosynthesis.