The primary process by which plants convert sunlight into energy is called photosynthesis. During this process, plants use sunlight to transform carbon dioxide and water into glucose and oxygen. The chlorophyll in plant leaves absorbs sunlight, and this energy powers the chemical reactions occurring in the chloroplasts. Photosynthesis is fundamental for life on Earth, as it serves as the foundation for the food chain and generates the oxygen required by living organisms. It's vital to note that this process not only provides energy for plants but also plays a crucial role in regulating atmospheric carbon levels.