Multiple Choice
Which of the following statements about the Calvin cycle is true?
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9. Photosynthesis
Calvin Cycle
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Why are 6 molecules of CO$_2$ required during the Calvin cycle to produce one molecule of glucose?
A
Because six CO$_2$ molecules are required to split water molecules during photosynthesis.
B
Because each CO$_2$ molecule is needed to regenerate ATP for the cycle.
C
Because six CO$_2$ molecules are needed to produce two molecules of pyruvate.
D
Because each CO$_2$ molecule contributes one carbon atom, and glucose contains six carbon atoms.
Verified step by step guidance1
Understand the structure of glucose: Glucose (C$_6$H$_{12}$O$_6$) is a six-carbon sugar molecule. This means that six carbon atoms are required to form one molecule of glucose.
Recognize the role of CO$_2$ in the Calvin cycle: Each molecule of CO$_2$ contributes one carbon atom to the process of building glucose during the Calvin cycle.
Recall the process of carbon fixation: In the Calvin cycle, CO$_2$ is fixed by the enzyme RuBisCO and incorporated into a 5-carbon molecule (ribulose-1,5-bisphosphate, or RuBP), forming a 6-carbon intermediate that quickly splits into two 3-carbon molecules.
Account for the number of CO$_2$ molecules: Since each CO$_2$ molecule provides one carbon atom, six CO$_2$ molecules are required to provide the six carbon atoms needed to synthesize one glucose molecule.
Connect the Calvin cycle to glucose production: The Calvin cycle must run multiple times (specifically six times) to fix six CO$_2$ molecules and produce the necessary intermediates that will eventually form one glucose molecule.
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