DENDROLOGY

Detailed explanation-1: -Carbon dioxide is a gas found in the air; plants can take in this gas through tiny holes in their leaves. Once they have water and carbon dioxide, they can use energy from sunlight to make their food. The leftovers from making the plant food is another gas called oxygen.

Detailed explanation-2: -Plants, like animals, take in oxygen and give out carbon dioxide during respiration. Only during photosynthesis, plants take in carbon dioxide and release oxygen as a byproduct.

Detailed explanation-3: -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. Therefore, it is said that during the daytime, plants take in carbon dioxide and give out oxygen, and during the night it is vice-versa.