Why is it necessary for 6 molecules of CO\(_2\) to enter the chloroplast during photosynthesis?

• A. To generate six molecules of ATP
• B. To produce one molecule of glucose (C\(_6\)H\(_{12}\)O\(_6\))
• C. To release six molecules of oxygen (O\(_2\))
• D. To initiate the light-dependent reactions

Answer: (B)

Verified step by step guidance

1. Understand the role of CO\(_2\) in photosynthesis: CO\(_2\) is a key reactant in the Calvin cycle, which is part of the light-independent reactions of photosynthesis. It is used to build glucose molecules through a series of enzymatic reactions.
2. Recall the chemical formula for glucose: Glucose has the molecular formula C\(_6\)H\(_{12}\)O\(_6\), meaning it contains six carbon atoms. These carbon atoms come from six molecules of CO\(_2\) that are fixed during the Calvin cycle.
3. Recognize the stoichiometry of the Calvin cycle: Each turn of the Calvin cycle fixes one molecule of CO\(_2\). To produce one molecule of glucose, the cycle must turn six times, requiring six molecules of CO\(_2\).
4. Understand the relationship between CO\(_2\) and oxygen release: While six molecules of CO\(_2\) are used in the Calvin cycle, oxygen (O\(_2\)) is released during the light-dependent reactions as a byproduct of water splitting, not directly related to CO\(_2\) fixation.
5. Clarify the role of ATP: ATP is generated during the light-dependent reactions and used as an energy source in the Calvin cycle to drive the synthesis of glucose. However, the entry of six molecules of CO\(_2\) is specifically tied to the production of one molecule of glucose, not directly to ATP generation.