Multiple Choice
Which energy transformation occurs during photosynthesis?
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9. Photosynthesis
Introduction to Photosynthesis
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In the process of photosynthesis, where do the electrons required to initiate Photosystem II originate?
A
From ATP hydrolysis
B
From carbon dioxide (CO$_2$) molecules
C
From the splitting of water (H$_2$O) molecules
D
From NADPH produced in the Calvin cycle
Verified step by step guidance1
Understand the role of Photosystem II in photosynthesis: Photosystem II is the first protein complex in the light-dependent reactions of photosynthesis. It captures light energy to excite electrons, which are then passed through the electron transport chain.
Recognize the source of electrons for Photosystem II: The electrons required to initiate Photosystem II come from the splitting of water (H$_2$O) molecules, a process known as photolysis.
Break down the photolysis process: Light energy absorbed by Photosystem II drives the splitting of water molecules into oxygen (O$_2$), protons (H$^+$), and electrons. The chemical reaction can be represented as: H$_2$O → 2H$^+$ + 2e$^-$ + 1/2 O$_2$.
Clarify why other options are incorrect: Electrons do not originate from ATP hydrolysis, carbon dioxide (CO$_2$) molecules, or NADPH produced in the Calvin cycle. These processes are involved in other aspects of photosynthesis but do not provide electrons for Photosystem II.
Summarize the importance of water splitting: The splitting of water molecules is essential for maintaining the flow of electrons in the light-dependent reactions, enabling the production of energy carriers like ATP and NADPH.
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