When a plant opens and closes its stomata, it is maintaining homeostasis. Homeostasis includes the regulation of carbon dioxide and water levels necessary to perform photosynthesis. It also allows the plants to store water to prevent them from dying
Respiration is the reverse of Photosynthesis.
I’m not 100% sure if this is a scientific theory but I’m going with the big bang theory. The big bang theory is a scientist best guess on how the world came to be. A 2013 map of the background radiation left over from the Big Bang, taken by the ESA's Planck spacecraft, captured the oldest light in the universe. This information helps astronomers determine the age of the universe.