Glycolysis and cellular respiration are catabolic pathways that release chemical potential energy of glucose in the readily usable form of ATP. In the cytosol, glucose is broken down into 3-carbon pyruvate molecules which either enters the mitochondria if O2 is available, or stays in the cytosol to undergo fermentation which makes NAD+ (a glycolysidic substrate) available for the process of glycolysis to continue.
Here are a few questions to help test your understanding.
- In the figure below: what are the three stages of cellular respiration (labels a, b, c)?
- What do the arrows labeled d represent?
- In the figure below: specify if ATP is produced by substrate-level phosphorylation OR oxidative phosphorylation (labels e, f, g).
- In the reaction: C6H12O6 + 6 O2 → 6 CO2 + 6 H20, what becomes reduced and what becomes oxidized?
- How many molecules of CO2 are generated for each molecule of acetyl-CoA introduced into the citric acid cycle?
- Provide the correct terms for the labels of the diagram below. Grey balls represent carbon atoms.
- What is the role of oxygen in cellular respiration?
- Provide terms for the labels of the oxidative phosphorylation diagram below.
- What are the numbers for the tally of ATP yield from the oxidation of one glucose molecule? Use the diagram below to add the tally from each of the processes.
- Why does fermentation produce less ATP than cellular respiration?
- At what point do fats enter the catabolic pathway? At what point do proteins enter the catabolic pathway?
HTK General Biology 2 
#1. a) Glycolysis b) Pyruvate Processing and Citric Acid Cycle c) Chemiosmosis
#2. They represent the movement of the NADH and FADH2 molecules towards the electron transport chain in order to deposit their electrons in that chain.
#3. e) substrate-level phosphorylation f) substrate-level phosphorylation g) oxidative phosphorylation
#4. Glucose is oxidized and O2 is reduced.
#5. 2 CO2 molecules
#6. a) pyruvate b) CO2 c) NADH d) Coenzyme A e) Acetyl CoA f) oxaloacetate g) citrate h)NADH i) CO2 j) CO2 K) NADH l) ATP m) FADH2 n) NADH
#7. O2 is the final electron acceptor in the ETC. Without O2, the ETC would shut down and no ATP would be produced via chemiosmosis (oxidative phosphorylation).
#8. a) lumen of the cristae b) inner membrane of mitochondria c) mitochondrial matrix
d) electron transport chain e) NADH f) NAD+ g) FADH2 h) O2 i) H2O j) chemiosmosis k) ATP synthase l) ADP and Pi m) ATP
#9. a) -2 (energy investment)
b) 4
c) citric acid cycle
d) 25
e) 29
I don’t understand what is meant in f)g)h)i) …
#10. In cellular respiration, the ETC is working and the final electron acceptor is O2. The energy difference between O2 and NADH is very big, therefore the ETC is able to generate a much greater proton motive force than with another proton acceptor, hence explaining why a lot more ATP can be produced as opposed to when another electron acceptor is used.
In fermentation, the ETC is not functional for lack of O2. Pyruvate therefore accepts electrons from NADH so that the cell can continue doing glycolysis and producing ATP (only 2 ATPs per molecule of glucose, which is much less than what is produced during cellular respiration).
#11. Fats enter the catabolic pathway when there are no more carbohydrates left to fuel cellular respiration. Proteins enter the catabolic pathway when there are no more fats left to fuel cellular respiration.
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Answer 1c) Electron Transport Chain + Chemiosmosis
Answers for questions 2 to 7 are perfect!
Answer for 8 also correct with some clarification 8a) can also be called intermembrane space, 8h) H+ and O2
Answer 9: a) -2, b) +4, c) citric acid cycle, d) 26 or 28, e) 32, f) 2, g) 6, h)2, i) 2
Answer 10: Seems good except that I worry that you refer to O2 in terms of energy. Otherwise the logic of missing out on the ETC is key (the NADH generated in glycolysis is not used in the ETC) and, pyruvate still contains most of the electrons that were present in glucose…pyruvate still has lots of potential energy which is processed in the citric acid cycle (but not in fermentation).
Incorrect answer for question 11.
Answer 11: Fats metabolism enters the citric acid cycle via acetyl-CoA (2 carbons at a time)
Proteins and fats both can be converted to intermediates of glycolysis or the citric acid cycle.
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3. Just to make sure if I understand the difference between the two, substrate level phosphorylation is the making of ATP directly form ADP and phosphate whereas oxidative phosphorylation is the making of ATP through the electron transport chain and chemiosmosis.
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Oxidative phosphorylation is the ATP produced from the chemiosmosis of H+ from the ETC that uses O2 as the final electron acceptor.
Any other ATP production is substrate-level phosphorylation.
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