Final answer:
Photosynthesis is the process in plants that produces molecular oxygen as a byproduct, during the conversion of carbon dioxide and water into glucose. Cellular respiration, on the other hand, is a process that consumes oxygen and is exergonic. Photosynthesis is endergonic as it requires energy from sunlight.
Step-by-step explanation:
The reaction in plants that produces molecular oxygen (O₂) is photosynthesis. During photosynthesis, green plants convert carbon dioxide and water into glucose and release oxygen as a byproduct. This is in contrast to cellular respiration, which consumes oxygen to break down glucose for energy, and fermentation processes, such as alcoholic and lactic acid fermentation, which occur in the absence of oxygen (anaerobically) and do not produce oxygen.
Regarding the types of reactions, cellular respiration is an exergonic process, as it releases energy. Photosynthesis is an endergonic process because it requires energy input in the form of sunlight to convert carbon dioxide and water into glucose and oxygen. Catabolic reactions, which break down molecules, are generally exergonic, while anabolic reactions, which build complex molecules from simpler ones, are endergonic.