Govt. Exams
Entrance Exams
The quantum requirement is about 8 photons per CO2 fixed (4 for PSII and 4 for PSI to generate sufficient ATP and NADPH for the Calvin cycle).
While red light activates phytochrome and initiates de-etiolation, it alone is insufficient for complete chloroplast development and normal growth. Blue light and other wavelengths are also required.
The Z-scheme produces approximately 1.5 ATP per NADPH (or 3 ATP per 2 NADPH) due to the proton gradient and energy requirements in the electron transport chain.
RuBisCO has dual specificity. When O2/CO2 ratio is high (low CO2, high O2), the oxygenase activity dominates, leading to photorespiration.
The Calvin cycle requires 3 ATP and 2 NADPH for each CO2 fixed. One ATP is used in the carboxylation step, and 2 ATP are used in the reduction phase to regenerate RuBP.
Bundle sheath cells in C4 plants contain large chloroplasts with well-developed grana for the Calvin cycle, unlike mesophyll cells.
In the Hatch-Slack pathway, PEP carboxylase catalyzes formation of oxaloacetate (4-carbon compound) in mesophyll cells.
When light is saturating, CO2 becomes the limiting factor as RuBisCO activity depends on substrate availability.
Chloroplasts synthesize amino acids using carbon skeletons from the Calvin cycle and nitrogen from nitrite reduction.
RuBisCO catalyzes oxygenation of RuBP instead of carboxylation under high O2/CO2 ratios, initiating the photorespiratory pathway.
