Which atmospheric molecule is required for the Calvin cycle in photosynthesis?

• A. Nitrogen ($N_2$)
• B. Carbon dioxide (${\mathrm{CO}}_2$)
• C. Oxygen ($O_2$)
• D. Methane (${\mathrm{CH}}_4$)

Answer: (B)

Verified step by step guidance

1. Understand the Calvin cycle: The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts in photosynthetic organisms. It is a part of the photosynthesis process where carbon fixation takes place.
2. Identify the role of carbon dioxide: In the Calvin cycle, carbon dioxide ( ${CO2}_{}$ ) is the molecule that is fixed into organic molecules. This process is essential for the synthesis of glucose and other carbohydrates.
3. Consider the options: Evaluate the given options - Nitrogen ( ${N2}_{}$ ), Oxygen ( ${O2}_{}$ ), Methane ( ${CH4}_{}$ ), and Carbon dioxide ( ${CO2}_{}$ ).
4. Determine the correct molecule: Recognize that Carbon dioxide ( ${CO2}_{}$ ) is the molecule required for the Calvin cycle as it is the source of carbon for the synthesis of glucose.
5. Conclude the reasoning: Conclude that Carbon dioxide ( ${CO2}_{}$ ) is the correct answer because it is the atmospheric molecule that participates directly in the Calvin cycle during photosynthesis.