Of the following, which occurs during the Calvin cycle?

• A. Light energy is converted to chemical energy.
• B. ATP and NADPH are synthesized.
• C. Excited electrons are conveyed from chlorophyll to an electron acceptor.
• D. Photons are absorbed.
• E. CO₂ is reduced.

Answer: (E)

Verified step by step guidance

1. Understand that the Calvin cycle is a part of photosynthesis that occurs in the stroma of chloroplasts and does not directly require light, hence it is also known as the light-independent reactions or dark reactions.
2. Recognize that the main purpose of the Calvin cycle is to convert carbon dioxide (CO2) into glucose, a process that involves the reduction of CO2.
3. Identify that during the Calvin cycle, ATP and NADPH produced in the light-dependent reactions are used to drive the endergonic reactions that reduce CO2 to form glyceraldehyde-3-phosphate (G3P), a precursor to glucose.
4. Note that the Calvin cycle involves three main phases: carbon fixation, reduction phase, and regeneration of ribulose bisphosphate (RuBP). The reduction phase is where CO2 is reduced.
5. Conclude that the correct answer is 'CO2 is reduced' because this is the key process that occurs during the Calvin cycle, distinguishing it from the light-dependent reactions where light energy is converted to chemical energy, ATP and NADPH are synthesized, and photons are absorbed.