CLEP Biology Cellular Respiration and Photosynthesis 4

Question 1

What is the role of ubiquinone (Coenzyme Q) in the electron transport chain?

Accepted Answer

It accepts electrons from Complexes I and II and shuttles them to Complex III

Answer

Ubiquinone is a mobile, lipid-soluble electron carrier that collects electrons from both Complex I and Complex II and delivers them to Complex III.

Question 2

How many ATP molecules are produced per NADH oxidized by the mitochondrial electron transport chain (using the P/O ratio of ~2.5)?

Accepted Answer

2.5 ATP

Answer

Modern measurements of the P/O ratio indicate that approximately 2.5 ATP molecules are synthesized per NADH oxidized, replacing the older estimate of 3 ATP.

Question 3

Photorespiration in C3 plants occurs when Rubisco fixes oxygen instead of CO2. What is the net effect on the plant?

Accepted Answer

It consumes ATP and releases CO2, reducing photosynthetic efficiency

Answer

When Rubisco reacts with O2 (oxygenase activity), the products enter the photorespiratory pathway, which consumes ATP and NADPH and releases CO2 without producing sugar.

Question 4

In non-cyclic electron flow (the Z-scheme), what is the ultimate electron donor and acceptor?

Accepted Answer

H2O is the donor; NADP+ is the acceptor

Answer

Water (H2O) donates electrons (via the OEC to PSII), and NADP+ is the final electron acceptor, being reduced to NADPH by ferredoxin-NADP+ reductase at PSI.

Question 5

Which of the following best explains why the inner mitochondrial membrane must be impermeable to protons (H+)?

Accepted Answer

To maintain the proton gradient necessary for ATP synthesis by ATP synthase

Answer

The impermeability of the inner membrane to H+ is essential because the proton gradient (proton-motive force) is the driving force for ATP synthase; any leak would dissipate the gradient and uncouple oxidative phosphorylation.

CLEP Practice Test

CLEP Practice Test

CLEP Biology Cellular Respiration and Photosynthesis 4