[Campbell Biology P.240] Although the Calvin cycle is sometimes referred to as the “dark rea... | Practice Question

Although the Calvin cycle is sometimes referred to as the “dark reactions” or “light-independent reactions,” why does it typically occur during daylight in most plants?

  • A: The Calvin cycle directly absorbs light to catalyze its reactions.
  • B: The enzymes required for the Calvin cycle are only active in the presence of light.
  • C: The Calvin cycle relies on ATP and NADPH, which are exclusively produced by the light reactions that require light.
  • D: Carbon fixation, a key step in the Calvin cycle, only occurs when stomata are open in daylight, allowing CO2 entry.

Explanation

The text states: 'the Calvin cycle in most plants occurs during daylight, for only then can the light reactions provide the NADPH and ATP that the Calvin cycle requires.' This highlights that despite being 'light-independent' in terms of direct light absorption, its reliance on the products of light reactions ATP and NADPH makes it dependent on light indirectly.