Plant Physiology and Photosynthesis Flashcards
7 cards from real USABO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Plant Physiology and Photosynthesis flashcards as text
Rubisco is described as having 'dual catalytic specificity.' Which statement correctly describes this property?
Answer: It can catalyze both carboxylation and oxygenation of RuBP
Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes carboxylation of RuBP producing 3-PGA for the Calvin cycle, and oxygenation of RuBP initiating the wasteful photorespiration pathway.
In non-cyclic photophosphorylation, which molecule serves as the ultimate electron donor?
Answer: Water (H2O)
Water is oxidized at the oxygen-evolving complex of PS II, donating electrons that flow through the entire photosynthetic electron transport chain to ultimately reduce NADP+.
How does cyclic photophosphorylation differ from non-cyclic photophosphorylation?
Answer: It produces only ATP without net generation of NADPH or O2
In cyclic photophosphorylation, electrons from excited PS I cycle back through the cytochrome b6f complex to generate a proton gradient for ATP synthesis, but no NADP+ is reduced and no water is split.
How many molecules of CO2 must be fixed by the Calvin cycle to produce one net molecule of glucose (C6H12O6)?
Answer: 6
Six CO2 molecules are fixed (one per carbon in glucose), requiring 18 ATP and 12 NADPH in three full turns of the Calvin cycle to produce one glucose molecule.
The P680 designation for the Photosystem II reaction center chlorophyll refers to what property?
Answer: It absorbs light most efficiently at a wavelength of 680 nm
P680 denotes the special pair of chlorophyll a molecules in the PS II reaction center whose absorption maximum lies at 680 nm, making it the highest-energy reaction center in oxygenic photosynthesis.
In CAM (Crassulacean Acid Metabolism) plants, when do stomata typically open, and why?
Answer: At night, to fix CO2 into organic acids while minimizing water loss
CAM plants open stomata at night to fix CO2 via PEP carboxylase into malate stored in vacuoles, then close stomata during the day when malate is decarboxylated and the Calvin cycle proceeds.
What is the direct product of the carbon reduction step (Stage 2) of the Calvin cycle, produced using both ATP and NADPH?
Answer: Glyceraldehyde-3-phosphate (G3P)
3-PGA is first phosphorylated by ATP to 1,3-bisphosphoglycerate, then reduced by NADPH to produce G3P, the first stable carbohydrate of photosynthesis used for sucrose and starch synthesis.