When Do Plants Breathe?
Technically, plants don’t breathe. But plants do respire. Like animals, they use oxygen in the process of breaking down carbohydrates, and use the energy released for basic metabolic functions such as repairing and replacing tissues, and building complex molecules like proteins and oils. During respiration, plants, like us, release carbon dioxide and water vapor.
Plants only photosynthesize in the presence of light, but they are continuously respiring, day and night. Even so, overall they release much more oxygen during photosynthesis than they consume during respiration!
The effect of the plants’ feeding and respiration system is that they exhale oxygen during the day and carbon dioxide during the night. This is the reason for the old custom in hospitals of removing plants and flowers from the wards at night and bringing them back in the morning.
Without enough plants, the world’s atmosphere would not be replenished with sufficient oxygen for the human race to survive. Generally plants respire more slowly the colder it becomes. Some plants, including many trees, go into a form of hibernation during the winter, with their respiring reduced to a minimum.