CLEP Biology Cellular Respiration and Photosynthesis 3 — Questions and Answers
Question 1: What is the net ATP yield from the complete aerobic oxidation of one glucose molecule (theoretical maximum)?
- 2 ATP
- 8 ATP
- 30-32 ATP (Correct answer)
- 38-40 ATP
Correct answer: 30-32 ATP
Modern estimates place the net ATP yield at 30-32 ATP per glucose, accounting for the P/O ratio of the ATP synthase and the cost of transporting pyruvate and ADP/ATP across mitochondrial membranes.
Question 2: In C4 plants, where does initial CO2 fixation occur, and what is the first stable product?
- Bundle sheath cells; 3-phosphoglycerate (3-PGA)
- Mesophyll cells; oxaloacetate (OAA) (Correct answer)
- Stomatal guard cells; malate
- Chloroplast stroma; ribulose-1,5-bisphosphate
Correct answer: Mesophyll cells; oxaloacetate (OAA)
In C4 plants, CO2 is initially fixed in mesophyll cells by PEP carboxylase to form oxaloacetate, a 4-carbon compound, which is then shuttled to bundle sheath cells.
Question 3: Which Complex of the electron transport chain is inhibited by cyanide?
- Complex I (NADH dehydrogenase)
- Complex II (succinate dehydrogenase)
- Complex III (cytochrome bc1)
- Complex IV (cytochrome c oxidase) (Correct answer)
Correct answer: Complex IV (cytochrome c oxidase)
Cyanide binds to the iron in the heme group of cytochrome c oxidase (Complex IV), blocking the final transfer of electrons to oxygen.
Question 4: The chemiosmotic theory proposes that ATP synthesis is driven by which gradient?
- A sodium ion concentration gradient across the plasma membrane
- A proton (H+) electrochemical gradient across the inner mitochondrial membrane (Correct answer)
- An electron potential difference between NADH and FADH2
- A phosphate concentration gradient in the matrix
Correct answer: A proton (H+) electrochemical gradient across the inner mitochondrial membrane
Peter Mitchell's chemiosmotic theory holds that protons pumped across the inner mitochondrial membrane by the ETC create a proton-motive force that drives ATP synthase (Complex V).
Question 5: In the Calvin cycle, what is the immediate product after CO2 is fixed by Rubisco onto ribulose-1,5-bisphosphate (RuBP)?
- Two molecules of 3-phosphoglycerate (3-PGA) (Correct answer)
- One molecule of glyceraldehyde-3-phosphate (G3P)
- One molecule of oxaloacetate
- Two molecules of glycerate
Correct answer: Two molecules of 3-phosphoglycerate (3-PGA)
Rubisco catalyzes the carboxylation of RuBP (5C) with CO2, and the unstable 6-carbon intermediate immediately splits into two molecules of 3-phosphoglycerate (3C each).
Question 6: Which molecule acts as the electron carrier between the citric acid cycle and the electron transport chain?
- ATP
- FADH2 and NADH (Correct answer)
- Acetyl-CoA
- Oxaloacetate
Correct answer: FADH2 and NADH
NADH and FADH2 produced in the citric acid cycle carry high-energy electrons to the electron transport chain embedded in the inner mitochondrial membrane.
Question 7: CAM plants (Crassulacean Acid Metabolism) minimize water loss by doing what?
- Fixing CO2 only during daylight with stomata open
- Opening stomata at night to fix CO2 as malate, then using it during the day (Correct answer)
- Eliminating photorespiration entirely by concentrating CO2 in bundle sheath cells
- Using PEP carboxylase instead of Rubisco at all times
Correct answer: Opening stomata at night to fix CO2 as malate, then using it during the day
CAM plants open their stomata at night to take in CO2 and store it as malate; during the day, stomata close and malate is decarboxylated to release CO2 for the Calvin cycle.
CLEP Biology Cellular Respiration and Photosynthesis 3
What is the net ATP yield from the complete aerobic oxidation of one glucose molecule (theoretical maximum)?