Plants make food during the day, but they use the food they already stored at night. During the day: Plants use sunlight for photosynthesis → they make glucose (food) and store some of it as starch. At night: There is no sunlight, so photosynthesis stops (or becomes negligible), but the plant uses the stored sugars/starch for energy. Plants also respire day and night. They use oxygen to break down sugars and release energy needed for growth, repair, and other activities. So, sunlight isn't needed continuously. It's mainly needed to produce the food that the plant can then use later.