Nitrogen assimilation is a process that requires considerable amounts of reducing power. In leaf cells under
moderate light conditions, this process competes with carbon assimilation in the Calvin cycle for reductants
supplied by the photosystem, if these reactions are coexistent. Such competition influences the carbon
assimilation quotient (CAQ), defined as the ratio of the CO2 absorption rate to the O2 evolution rate. CAQ is
also influenced by the nitrogen source applied to plants; deltaCAQ = CAQ(ammonium) - CAQ(nitrate). Figure 2
shows deltaCAQ values as a function of leaf internal CO2 concentration (Ci) in various C3 and C4 plant species:
in C3 plants, deltaCAQ is high at low Ci and drops toward near zero as Ci increases; in C4 plants, deltaCAQ
stays low and roughly flat across all Ci values shown.
Figure 1.
Figure 2.
Using the information and data, determine which of the statements are true or which are false.
Q35-1. Choose the appropriate answer set to fill in the blanks: Competition for reductants between nitrogen assimilation and carbon assimilation (A) CAQ. As application of ammonium skips its upstream steps of nitrogen assimilation, deltaCAQ correlates (B) with the activity of the nitrate-to-ammonium conversion process of nitrogen assimilation.
Q35-2. In C4 plants, which cell is likely to be responsible for the nitrate-to-ammonium and ammonium-to-glutamate processes of nitrogen assimilation?
Figure 1.
Figure 2.