2. Why is the oxygen production of the plants different at different times of the day?

Explanation:

Plants give out carbon dioxide not only at night but during the day too. It happens because of the process of respiration in which plants take in oxygen and give out carbon dioxide. As soon as the sun rises another process called photosynthesis starts, in which carbon dioxide is taken in and oxygen is given out hence, whenever plants get sunlight during day they'll produce more oxygen and less in shadow or shady place.

it will increase due to the time span

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.