A: begin to cool and daylight hours decrease.
Plants go through seasonal changes from summer to fall because of the changes in temperature and the length of daylight hours. As summer ends and fall begins, temperatures begin to cool down and the days become shorter. This change in temperature and daylight hours triggers physiological changes in plants, such as the slowing down of growth and the production of pigments like anthocyanins, which give leaves their characteristic red and orange colors in the fall. These changes allow the plant to prepare for the colder winter months and conserve energy for the upcoming spring growth season.