Which statement is true about carbon fixation in C3 plants?

Which statement is true about carbon fixation in C3 plants?

• A. C3 plants fix carbon directly through the Calvin cycle.
• B. C3 plants use a four-carbon compound to fix carbon.
• C. CAM plants fix carbon at night.
• D. CAM plants fix carbon via the Calvin cycle in the light.

Answer: (A)

C3 plants fix carbon directly through the Calvin cycle. In these plants, CO2 enters the chloroplasts and is fixed by Rubisco to form a three-carbon compound that feeds the Calvin cycle, using ATP and NADPH from the light reactions to build sugars. There’s no prior step creating a four-carbon molecule—that’s a feature of C4 plants. CAM plants, in contrast, store CO2 as malate at night and only use it for the Calvin cycle during the day, so carbon fixation is not happening in the Calvin cycle at night in CAM plants.