Final answer:
The correct evolutionary order of metabolic breakthroughs is: fermentation, oxygen-producing photosynthesis, anoxygenic photosynthesis, and oxygen-dependent ATP synthesis, which corresponds to option (b) C, A, B, D.
Step-by-step explanation:
To determine the correct order in which breakthroughs in energy metabolism are thought to have evolved, we must first consider the historical environment and progression of metabolic pathways. It is known that the earliest forms of life had to operate under anaerobic conditions, as the atmosphere lacked oxygen.
The sequence would likely start with metabolic processes that do not require oxygen, evolving to those that use oxygen as it became available in the atmosphere.
- Anoxygenic photosynthesis (light-dependent transfer of electrons from H2S to NADPH) likely started early, using molecules like H2S rather than H2O, and thus did not produce free oxygen.
- Fermentation (anaerobic metabolism - the consumption of fermentable organic acids) is also an ancient process, utilized before the atmosphere contained significant oxygen.
- The evolution of oxygen-producing photosynthesis (H2O-splitting enzyme activity) marked a major shift, as it began to produce oxygen, shaping the composition of the Earth's atmosphere.
- Finally, oxygen-dependent ATP synthesis (such as the electron transport chain and oxidative phosphorylation) arose once there was enough oxygen in the atmosphere to support such metabolism.
Therefore, the correct order of the evolutionary emergence of these processes is (b) C, A, B, D: the consumption of fermentable organic acids, H2O-splitting enzyme activity, light-dependent transfer of electrons from H2S to NADPH, and oxygen-dependent ATP synthesis.