Seasonal CO2 Fluctuations from Plant Activity

Steps:

• Recognize annual CO2 variations as seasonal cycles observed in data like Mauna Loa measurements.
• Link summer lows to Northern Hemisphere vegetation growth.
• Identify photosynthesis as the process absorbing CO2 during active plant seasons.
• Contrast with winter highs from reduced absorption and ongoing respiration.

Why A is correct:

• Photosynthesis uses CO2 to produce glucose (6CO2 + 6H2O → C6H12O6 + 6O2), increasing in summer to lower atmospheric CO2 levels.

Why the others are wrong:

• B: Winter respiration releases CO2 but does not cause the full yearly variation; it's secondary to summer uptake.
• C: Rainfall influences plant growth indirectly but does not directly drive consistent CO2 concentration cycles.
• D: Global warming causes long-term CO2 rise, not the observed annual seasonal dips and peaks.

Final answer: A