AP BIOLOGY

Detailed explanation-1: -A carbon sink absorbs carbon dioxide from the atmosphere. The ocean, soil and forests are the world’s largest carbon sinks.

Detailed explanation-2: -But during night time, plants perform only respiration and no photosynthesis (since absence of sunlight). Thus concentration of CO2 released is higher during night time.

Detailed explanation-3: -Typically, carbon dioxide levels rise during the night when people are sleeping, especially if the door and windows are closed. The concentrations then fall during the day if the room is unoccupied.

Detailed explanation-4: -But during the day, the amount of carbon dioxide released is much less than the amount required for photosynthesis. So, plants take in carbon dioxide from the atmosphere for preparing food. At night, photosynthesis does not occur hence they take in oxygen and give out carbon dioxide.