The primary energy source for photosynthesis is sunlight. During this process, plants, algae, and some bacteria capture light energy using chlorophyll, a pigment found primarily in chloroplasts. This energy is then used to convert carbon dioxide from the air and water from the soil into glucose, a sugar that provides energy for the plant's growth and development. In addition to glucose, oxygen is released as a byproduct, which is essential for the respiration of most living organisms. Thus, sunlight is fundamental to sustaining life on Earth through the energy cycle.