Final answer:
Plants release oxygen during the day due to photosynthesis, a process that requires sunlight. At night, plants cannot perform photosynthesis and therefore do not release oxygen.
Step-by-step explanation:
Plants release oxygen during the day but not during the night because of a process called photosynthesis. Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to produce glucose (a type of sugar) and oxygen. During the day, when there is sunlight, plants perform photosynthesis and release oxygen as a byproduct. However, at night, plants do not have access to sunlight, so they cannot perform photosynthesis and therefore do not release oxygen.
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