Multiple Choice
What is the basic role of \( \mathrm{CO}_2 \) in photosynthesis?
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9. Photosynthesis
Introduction to Photosynthesis
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What is the role of water ($H_2O$) in photosynthesis?
A
It directly fixes carbon dioxide into glucose.
B
It serves as the main pigment absorbing light energy.
C
It acts as the primary energy source for the Calvin cycle.
D
It donates electrons to replace those lost by chlorophyll during the light reactions.
Verified step by step guidance1
Understand the process of photosynthesis, which consists of two main stages: the light-dependent reactions and the Calvin cycle (light-independent reactions). Water ($H_2O$) plays a critical role in the light-dependent reactions.
In the light-dependent reactions, chlorophyll molecules in the thylakoid membrane absorb light energy, which excites their electrons. These excited electrons are transferred to the electron transport chain, leaving chlorophyll molecules electron-deficient.
Water ($H_2O$) is split in a process called photolysis, which occurs in the thylakoid lumen. This splitting of water produces oxygen gas ($O_2$), protons ($H^+$), and electrons.
The electrons released from the splitting of water are donated to chlorophyll to replace the electrons lost during excitation. This ensures the continuity of the light-dependent reactions.
Recognize that water does not directly fix carbon dioxide, act as a pigment, or serve as the primary energy source for the Calvin cycle. Its primary role is to donate electrons to chlorophyll during the light reactions, enabling the process of photosynthesis to proceed efficiently.
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