The main source of energy for plants is sunlight, which they harness through the process of photosynthesis. In this process, plants use chlorophyll in their leaves to capture sunlight and convert it into chemical energy. This energy is used to transform carbon dioxide from the air and water from the soil into glucose, a simple sugar that serves as food for the plant. Oxygen is released as a byproduct. Through photosynthesis, plants not only sustain themselves but also produce oxygen, making them essential for life on Earth, as they are at the base of the food chain.