1. Why do O2 evolution curves display lag periods?

A lag period should not be a new concept to you; you also saw a lag phase during the yeast fermentation experiment. Both photosynthesis and cellular respiration involve enzymes that act upon molecules within the cell. You will recall that the light-independent reactions involve the cyclic process called the Calvin-Benson cycle. During the Calvin-Benson cycle, carbon (from CO2) passes through a number of molecular forms on the way to producing more of the CO2 acceptor (RUBP) and photosynthesis end-products, such as glucose and starch. The Calvin-Benson cycle will operate at maximum speed only when the chloroplast contains adequate quantities of these molecules. The lag phase occurs after the light is turned on until the levels of molecules reach operating levels.

 

For biology majors: To learn about the 'metabolic pool' concept, click here.

 

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