The primary source of energy for plants is sunlight. Through a process called photosynthesis, plants capture sunlight using chlorophyll in their leaves. This energy is used to convert carbon dioxide from the air and water from the soil into glucose, a sugar that serves as food and energy for the plant. Photosynthesis not only provides nourishment for plants but also produces oxygen as a by-product, which is vital for life on Earth. This process is fundamental to sustaining the ecosystem, as plants form the base of the food chain.