Final answer:
The endergonic reaction is CO2 + H2O -> glucose, which is part of the energy-requiring process of photosynthesis, converting solar energy into stored chemical energy. In contrast, reactions like ATP -> ADP + Pi are exergonic, releasing energy.
Step-by-step explanation:
The reaction that represents an endergonic reaction is CO2 + H2O -> glucose. This reaction is part of photosynthesis, which is a process that requires energy to convert carbon dioxide and water into glucose, a form of chemical energy stored in the bonds of sugar molecules. This process occurs in the chloroplasts of plants and is fundamentally important for the conversion of solar energy into chemical energy.
In contrast, the other reactions listed are either part of cellular respiration or the ATP cycle, where ATP -> ADP + Pi is an exergonic reaction as it releases energy when a phosphate group is removed from ATP. Similarly, the breakdown of glucose during glycolysis and cellular respiration is exergonic, as it releases energy used to generate ATP from ADP and Pi. These reactions are crucial in biology, as they maintain the energy balance necessary for cellular functions.