Biology – Photosynthesis as an energy transfer process | e-Consult
Photosynthesis as an energy transfer process (1 questions)
The Calvin cycle is entirely dependent on the light-dependent reactions because it requires a continuous supply of ATP and NADPH, which are produced during the light-dependent reactions. Without the light-dependent reactions functioning, the Calvin cycle would quickly cease to operate.
ATP's Role and Consequences of Absence: The Calvin cycle needs ATP for the initial phosphorylation of RuBP and for various reduction steps. If the light-dependent reactions cease, ATP production stops. This would lead to a rapid depletion of the ATP supply within the stroma. Without sufficient ATP, the carboxylation of RuBP would halt, and the subsequent reduction reactions would also stall.
NADPH's Role and Consequences of Absence: The Calvin cycle requires NADPH to provide the reducing power for the conversion of PGA to G3P. If the light-dependent reactions cease, NADPH production stops. This would lead to a rapid depletion of the NADPH supply. Without sufficient NADPH, the reduction reactions would halt, and PGA would accumulate. The Calvin cycle would be unable to proceed.
Overall Impact: The absence of the light-dependent reactions would effectively shut down the Calvin cycle. CO2 fixation would cease, and the production of glucose and other organic molecules would stop. The plant would be unable to produce the sugars it needs for growth and metabolism. Essentially, the light-dependent reactions provide the necessary energy and reducing power to "fuel" the Calvin cycle, making the two stages interdependent.