In the context of organic chemistry, how are the dark reactions in plants dependent on the light reactions?

• A. Dark reactions occur only during the night when light reactions are inactive.
• B. Dark reactions use $\mathrm{ATP}$ and $\mathrm{NADPH}$ produced in light reactions to synthesize $C_6{H}_{12}{O}_6$ (glucose).
• C. Dark reactions directly convert sunlight into chemical energy.
• D. Dark reactions produce $O2$ as a byproduct of glucose synthesis.

Answer: (B)

Verified step by step guidance

1. Understand the two main stages of photosynthesis: light reactions and dark reactions (Calvin cycle). Light reactions occur in the thylakoid membranes and require sunlight to produce ATP and NADPH.
2. Recognize that dark reactions, also known as the Calvin cycle, occur in the stroma of chloroplasts and do not require light directly. Instead, they utilize the ATP and NADPH generated by the light reactions.
3. Clarify that the dark reactions use ATP and NADPH to convert carbon dioxide and water into glucose, a process known as carbon fixation.
4. Note that the term 'dark reactions' can be misleading, as these reactions can occur during the day as long as ATP and NADPH are available from the light reactions.
5. Understand that oxygen is not produced during the dark reactions; it is a byproduct of the light reactions when water is split to release electrons.