In physical changes no new materials are formed and the particles do not change apart from gaining or losing energy. ... Particles stay the same unless there is a chemical change whether the matter is solid, liquid or gas. Only their arrangement, energy and movement changes.
Answer: The balance of oxygen and carbondioxide is made due to respreration and photosinthesis. As we leave carbon dioxide and take in oxygen the ballance of carbon dioxide and oxygen is made. And during the photosinthesis of plants the balance of carbon dioxide and oxygen is made.