General Science • BiologyHard
During the light-dependent reactions of photosynthesis in green plants, what is the precise physiological source of electrons that replace those lost by Photosystem II when photo-excited?
A. Photolytic splitting of water molecules releasing oxygen gas✓ Correct Answer
B. Direct cyclic photophosphorylation of adenosine diphosphate
C. Reduction of atmospheric carbon dioxide molecules in the stroma
D. Oxidation of glucose molecules within mitochondrial cristae
💡 Solution & Explanation
Photosystem II abstracts electrons from water molecules during photolysis, a process catalyzed by an oxygen-evolving complex that splits water into oxygen gas, protons, and replacement electrons. Cyclic photophosphorylation recycles electrons through Photosystem I rather than splitting water. Carbon dioxide reduction occurs during the light-independent Calvin cycle in the stroma. Glucose oxidation takes place during cellular respiration rather than photosynthetic light reactions. Oxygen released during photolysis sustains aerobic life on Earth.
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