USABO Plant Physiology and Photosynthesis

Question 1

Which photosystem is responsible for the oxidation of water molecules during the light-dependent reactions of photosynthesis?

Accepted Answer

Photosystem II (P680)

Answer

Photosystem I (P700)

Answer

The cytochrome b6f complex

Answer

Ferredoxin-NADP+ reductase

Question 2

What is the primary CO2 acceptor molecule in the Calvin cycle that is carboxylated by Rubisco?

Accepted Answer

Ribulose-1,5-bisphosphate (RuBP)

Answer

3-phosphoglycerate (3-PGA)

Answer

Phosphoenolpyruvate (PEP)

Answer

Glyceraldehyde-3-phosphate (G3P)

Question 3

In C4 plants, which cell type performs initial CO2 fixation, and which enzyme catalyzes this reaction?

Accepted Answer

Mesophyll cells; PEP carboxylase

Answer

Bundle sheath cells; Rubisco

Answer

Guard cells; carbonic anhydrase

Answer

Mesophyll cells; Rubisco

Question 4

Which two products are generated by non-cyclic photophosphorylation (the Z-scheme) in photosynthesis?

Accepted Answer

ATP and NADPH

Answer

ATP and NADH

Answer

NADPH and O2 only

Answer

Glucose and ATP

Question 5

Photorespiration reduces photosynthetic efficiency primarily because it:

Accepted Answer

Releases previously fixed CO2 via the glycolate pathway

Answer

Increases the rate of ATP hydrolysis in chloroplasts

Answer

Enhances O2 production at the expense of NADPH

Answer

Inhibits the regeneration of RuBP in the Calvin cycle

Question 6

Chlorophyll a and chlorophyll b absorb light most efficiently in which wavelength ranges?

Accepted Answer

Blue-violet (400-450 nm) and red (650-700 nm)

Answer

Green (520-560 nm) and yellow (570-590 nm)

Answer

Ultraviolet (280-350 nm) and far-red (720-750 nm)

Answer

Red (650-700 nm) and infrared (>750 nm)

Question 7

What drives ATP synthesis by ATP synthase (CF0-CF1) in the thylakoid membrane during photosynthesis?

Accepted Answer

A proton electrochemical gradient across the thylakoid membrane

Answer

Direct electron transfer from reduced plastoquinone to ATP synthase

Answer

Substrate-level phosphorylation coupled to NADPH oxidation

Answer

Conformational changes in Rubisco coupled to ADP phosphorylation