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Unformatted text preview: c onv erted to 3 molec ules of R5P (als o 1 phos phate
group eac h). Thus there is a net releas e of 2 Pi.
In the s ec ond part of Phas e 3, 3 ATP molec ules are us ed to c onv ert the 3 R5P into 3 RuBP.
Note that in the entire c y c le, 9 ATP are hy droly z ed to ADP; 8 of the 9 phos phate groups are releas ed as Pi, and the ninth phos phate appears in
the G3P output from the c y c le. Part C Do the light reactions of photosynthesis depend on theCalvin cycle?
The rate of O2 produc tion by the light reac tions v aries with the intens ity of light bec aus e light is required as the energy s ourc e for O2 formation. Thus ,
lower light lev els generally mean a lower rate of O2 produc tion.
In addition, lower light lev els als o affec t the rate of CO2 uptak e by the Calv in c y c le. This is bec aus e the Calv in c y c le needs the ATP and NADPH
produc ed by the light reac tions . In this way , the Calv in c y c le depends on the light reac tions .
But is the inv ers e true as well? Do the light reac tions depend on the Calv in c y c le?
Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stom ata closed to conserve water).
Which statem ent correctly describes how O2 production would be affected? (Assum e that the light intensity does not change.) Hin t 1. How the supply of inputs to a reaction is related to the rate of the reaction
For mos t c hemic al reac tions , inc luding reac tions c ataly z ed by enz y mes , the reac tion rate (amount of produc t produc ed per unit of time)
depends on the s upply of s ubs trates (inputs ) for the reac tion. If the s upply of an input dec reas es , the rate of the reac tion als o tends to
dec reas e. Think about all the inputs to the light reac tions that c ould affec t its rate. Hin t 2. Are any outputs of the Calvin cycle also i...
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- Spring '14