USABO Plant Physiology and Photosynthesis 3

Question 1

Rubisco is described as having 'dual catalytic specificity.' Which statement correctly describes this property?

Accepted Answer

It can catalyze both carboxylation and oxygenation of RuBP

Answer

It can fix both CO2 gas and dissolved bicarbonate ions equally well

Answer

It functions in both the C3 and C4 carbon fixation pathways simultaneously

Answer

It can use both RuBP and PEP as substrates for carbon fixation

Question 2

In non-cyclic photophosphorylation, which molecule serves as the ultimate electron donor?

Accepted Answer

Water (H2O)

Answer

Ferredoxin

Answer

NADPH

Answer

Plastoquinone

Question 3

How does cyclic photophosphorylation differ from non-cyclic photophosphorylation?

Accepted Answer

It produces only ATP without net generation of NADPH or O2

Answer

It involves coordinated activity of both PS I and PS II

Answer

It requires more photons per ATP molecule synthesized

Answer

It occurs exclusively in the stroma rather than thylakoid membranes

Question 4

How many molecules of CO2 must be fixed by the Calvin cycle to produce one net molecule of glucose (C6H12O6)?

Accepted Answer

6

Answer

3

Answer

12

Answer

9

Question 5

The P680 designation for the Photosystem II reaction center chlorophyll refers to what property?

Accepted Answer

It absorbs light most efficiently at a wavelength of 680 nm

Answer

It is composed of 680 individual chlorophyll antenna molecules

Answer

It was structurally characterized in a 1980 landmark study

Answer

It transfers electrons at a rate of 680 per second under saturating light

Question 6

In CAM (Crassulacean Acid Metabolism) plants, when do stomata typically open, and why?

Accepted Answer

At night, to fix CO2 into organic acids while minimizing water loss

Answer

During the day, to maximize light-driven CO2 fixation efficiency

Answer

Only at dawn and dusk to balance carbon gain with water conservation

Answer

Continuously, because CAM plants tolerate high transpiration rates

Question 7

What is the direct product of the carbon reduction step (Stage 2) of the Calvin cycle, produced using both ATP and NADPH?

Accepted Answer

Glyceraldehyde-3-phosphate (G3P)

Answer

Ribulose-1,5-bisphosphate (RuBP)

Answer

Oxaloacetate (OAA)

Answer

Phosphoglycerate kinase product