Which Process Probably Evolved First on the Ancient Planet Earth

question 30

Multiple Choice

Which process probably evolved first on the ancient Planet Earth - photosynthesis or cellular respiration?

• A) Photosynthesis because it provided atmospheric oxygen that facilitated evolution of aerobic organisms.
• B) Cellular respiration because carbon dioxide from citric acid cycle provided source of carbon fixation for photosynthesis.
• C) Photosynthesis because there was plenty of light and CO₂ in the atmosphere for carbon fixation but no organic molecules to use as carbon and energy sources.
• D) Cellular respiration because it is the universal metabolic pathway.

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