How Do Plants Give off Oxygen?
Plants give off oxygen during the process of photosynthesis. Using green chlorophyll (which gives them their color), the leaves of plants use the energy of sunlight to change carbon dioxide and water into food the plant needs to live. During this process, oxygen is released into the air.
This oxygen is breathed in by animals. Animals, in turn, breathe carbon dioxide back into the air, where it is again used by plants to produce food and oxygen. Because of green plants, the amount of oxygen in the air has always remained at about the same level.
As photosynthesis requires sunlight, this process only happens during the day. We often like to think of this as plants `breathing in carbon dioxide and `breathing out oxygen. Just like animals, plants need to break down carbohydrates into energy. Oxygen is required to do this.
Then why do the plants get rid of oxygen they produce during photosynthesis?
The answer is, they do not. Plants actually hold on to a small amount of the oxygen they produced in photosynthesis and use that oxygen to break down carbohydrates to give them energy.
But what happens at night when there is no sunlight which is needed in photosynthesis?
Interestingly, in order to maintain their metabolism and continue respiration at night, plants must absorb oxygen from the air and give off carbon dioxide (which is exactly what animals do). Plants produce approximately ten times more oxygen during the day that what they consume at night.