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Photosynthesis and Photorespiration in C3, C4, and CAM Plants

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  • What is photorespiration and why is it harmful to plants?

    Photorespiration is a process that wastes energy by consuming O2 and organic fuels, releasing CO2 without producing sugar. It slows down photosynthesis and reduces plant efficiency.

  • Why do plants undergo photorespiration despite its drawbacks?

    Photorespiration helps plants avoid overheating by wasting energy on purpose when stomata close, protecting the plant under stress.

  • What characterizes C3 plants in photosynthesis?

    C3 plants produce a 3-carbon molecule as the first stable product of the Calvin cycle, have both light and dark reactions in the same mesophyll cell, and are most susceptible to photorespiration.

  • How many carbon fixation rounds occur in C3 plants?

    C3 plants perform one carbon fixation round per cycle.

  • What is the main advantage of C4 plants over C3 plants?

    C4 plants better avoid photorespiration by separating light and dark reactions into different cells and producing a 4-carbon intermediate.

  • Where do light and dark reactions occur in C4 plants?

    Light reactions occur in mesophyll cells, and dark reactions occur in bundle sheath cells.

  • How many carbon fixation rounds occur in C4 plants?

    C4 plants perform two carbon fixation rounds.

  • What role does the 4-carbon intermediate play in C4 plants?

    The 4-carbon intermediate supplies additional CO2 to the Calvin cycle when stomata close and CO2 levels are low, reducing photorespiration.

  • How do CAM plants avoid photorespiration?

    CAM plants separate carbon fixation rounds in time, opening stomata at night to fix CO2 and closing them during the day to reduce water loss and photorespiration.

  • Where do light and dark reactions occur in CAM plants?

    Both light and dark reactions occur in the same cell in CAM plants.

  • How many carbon fixation rounds occur in CAM plants?

    CAM plants perform two carbon fixation rounds separated by time (night and day).

  • When do CAM plants open their stomata and why?

    CAM plants open stomata at night when temperatures are cooler to fix CO2 and minimize water loss.

  • What happens when rubisco adds O2 instead of CO2 during photorespiration?

    Rubisco produces a two-carbon compound, consumes O2 and organic fuels, releases CO2, and wastes energy without producing sugar or heat.

  • Why are C3 plants more susceptible to photorespiration?

    Because both light and dark reactions occur in the same mesophyll cell and they do not have mechanisms to concentrate CO2, leading to more rubisco oxygenation.

  • What is the significance of spatial separation in C4 plants?

    Spatial separation of reactions into mesophyll and bundle sheath cells allows C4 plants to concentrate CO2 and reduce photorespiration.

  • What is the significance of temporal separation in CAM plants?

    Temporal separation allows CAM plants to fix CO2 at night and perform the Calvin cycle during the day, conserving water and reducing photorespiration.