CLEP Biology Cellular Respiration and Photosynthesis 2

Question 1

Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA during pyruvate oxidation?

Accepted Answer

Pyruvate dehydrogenase complex

Answer

The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA, releasing CO2 and reducing NAD+ to NADH.

Question 2

During the light-dependent reactions, what is the role of plastoquinone (PQ)?

Accepted Answer

It shuttles electrons from PSII to the cytochrome b6f complex

Answer

Plastoquinone carries electrons from Photosystem II to the cytochrome b6f complex, also pumping H+ ions into the thylakoid lumen.

Question 3

In the citric acid cycle, which step directly produces GTP (or ATP)?

Accepted Answer

Succinyl-CoA → succinate

Answer

The conversion of succinyl-CoA to succinate by succinyl-CoA synthetase is the only substrate-level phosphorylation step in the citric acid cycle.

Question 4

What is the primary function of the oxygen-evolving complex (OEC) in photosynthesis?

Accepted Answer

Splitting water to release O2 and replenish electrons to PSII

Answer

The OEC (also called the water-splitting complex) oxidizes water molecules, releasing O2 gas and providing electrons to replace those lost by P680 in Photosystem II.

Question 5

How many carbon atoms enter the citric acid cycle per turn via acetyl-CoA, and how many leave as CO2?

Accepted Answer

2 enter, 2 leave

Answer

Two carbons enter as acetyl-CoA and two carbons are released as CO2 (from isocitrate dehydrogenase and α-ketoglutarate dehydrogenase reactions) per turn.

CLEP Practice Test

CLEP Practice Test

CLEP Biology Cellular Respiration and Photosynthesis 2