Multiple Choice
In the light reactions of photosynthesis, which molecule acts as the final electron acceptor in the electron transport chain?
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9. Photosynthesis
Light Reactions of Photosynthesis
Multiple Choice
In noncyclic photophosphorylation during the light reactions of photosynthesis, which of the following occurs?
A
Glucose is directly synthesized from carbon dioxide
B
Oxygen is consumed as the final electron acceptor
C
Electrons flow from water to NADP\(^+\), producing NADPH and ATP
D
Electrons cycle back to photosystem I, producing only ATP
Verified step by step guidance1
Step 1: Begin by understanding the process of noncyclic photophosphorylation, which occurs during the light reactions of photosynthesis. This process involves the flow of electrons through the photosystems embedded in the thylakoid membrane of chloroplasts.
Step 2: Recognize that noncyclic photophosphorylation starts with the splitting of water molecules (photolysis) in Photosystem II. This releases electrons, protons (H extsuperscript{+}), and oxygen gas (O extsubscript{2}). The electrons are then energized by light absorbed by chlorophyll pigments in Photosystem II.
Step 3: Follow the path of the energized electrons as they move through the electron transport chain. The energy released during this transfer is used to pump protons across the thylakoid membrane, creating a proton gradient that drives ATP synthesis via chemiosmosis.
Step 4: Understand that the electrons eventually reach Photosystem I, where they are re-energized by light absorption. These high-energy electrons are then transferred to NADP extsuperscript{+}, along with protons, to form NADPH. This is a key distinction of noncyclic photophosphorylation, as the electrons do not return to Photosystem I but instead are used to reduce NADP extsuperscript{+}.
Step 5: Note that the products of noncyclic photophosphorylation are ATP and NADPH, which are essential for the Calvin cycle in the dark reactions of photosynthesis. Oxygen is released as a byproduct, and the flow of electrons originates from water and ends with NADP extsuperscript{+} reduction.
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