Photosynthesis is an endothermic reaction because it requires energy to proceed. This energy comes from sunlight, which is absorbed by chlorophyll in the chloroplasts of plant cells. The absorbed energy is used to convert carbon dioxide and water into glucose and oxygen. The products of photosynthesis, glucose and oxygen, have more energy than the reactants, carbon dioxide and water. This means that energy has been absorbed from the surroundings during the reaction, making it endothermic.
The light-dependent reactions of photosynthesis are the initial steps that capture sunlight energy. Chlorophyll molecules absorb photons of light, which excite electrons and initiate a chain of electron transport reactions. This process generates ATP, a molecule that stores energy in its chemical bonds, and NADPH, a carrier molecule that transfers electrons. The light-independent reactions, also known as the Calvin cycle, use the ATP and NADPH produced in the light-dependent reactions to convert carbon dioxide into glucose.
In summary, photosynthesis is an endothermic reaction because it requires energy input from sunlight to convert low-energy reactants into high-energy products. The absorbed energy is used to drive the chemical reactions that build glucose molecules, which store energy for the plant to use.
