What is the main advantage of C4 and CAM photosynthesis?

What is the main advantage of C4 and CAM photosynthesis?

• A. Are adapted to drought environments by closing stomata during the day.
• B. Increase photosynthesis rate in low light.
• C. Fix carbon without reducing photorespiration.
• D. Decrease photorespiration and minimize energy loss.

Answer: (D)

These pathways maximize carbon fixation by keeping CO2 levels high at the site of the Calvin cycle, which cuts down on the wasteful process called photorespiration that happens when Rubisco fixes O2 instead of CO2. In C4 systems, CO2 is first fixed into a four-carbon compound in the mesophyll with a high affinity for CO2, then CO2 is released near Rubisco in bundle-sheath cells. This concentration of CO2 around the enzyme limits oxygenation and the ensuing energy loss from photorespiration, making the overall process more efficient in hot, dry conditions. CAM plants do something similar but by timing CO2 capture to when water loss is minimal: they fix CO2 at night into organic acids and release it during the day for the Calvin cycle, again maintaining a high local CO2 concentration while conserving water. The takeaway is that both strategies reduce photorespiration and the associated energy waste, especially under conditions that promote stomatal closure or high temperatures.

These pathways maximize carbon fixation by keeping CO2 levels high at the site of the Calvin cycle, which cuts down on the wasteful process called photorespiration that happens when Rubisco fixes O2 instead of CO2. In C4 systems, CO2 is first fixed into a four-carbon compound in the mesophyll with a high affinity for CO2, then CO2 is released near Rubisco in bundle-sheath cells. This concentration of CO2 around the enzyme limits oxygenation and the ensuing energy loss from photorespiration, making the overall process more efficient in hot, dry conditions. CAM plants do something similar but by timing CO2 capture to when water loss is minimal: they fix CO2 at night into organic acids and release it during the day for the Calvin cycle, again maintaining a high local CO2 concentration while conserving water. The takeaway is that both strategies reduce photorespiration and the associated energy waste, especially under conditions that promote stomatal closure or high temperatures.