Transforming Sunlight into Chemical Energy Plants convert sunlight into vital chemical energy by absorbing photons through pigments in chloroplast thylakoids. In paired photosystems, these photons excite electrons and trigger the splitting of water, releasing oxygen as a byproduct. The energized electrons travel through an electron transport chain that creates a hydrogen ion gradient, powering ATP synthase. This process produces ATP and NADPH, which are essential for fueling the synthesis of glucose.
Converting Carbon Dioxide into Carbohydrates The Calvin cycle uses ATP and NADPH to transform carbon dioxide into glyceraldehyde 3-phosphate, the precursor to glucose. Carbon dioxide initially attaches to ribulose bisphosphate, forming a six-carbon molecule that splits into two three-carbon compounds. Successive reactions reduce these compounds and regenerate ribulose bisphosphate, enabling continuous carbon fixation. The cycle ultimately provides the sugars and structural molecules necessary for plant growth and global food webs.