The equation for cellular respiration is: C6H12O6 + 6O2 6CO2 + 6H2O. At what specific point in the cellular respiration process has glucose been broken down completely from a six carbon molecule to 6 molecules of CO2?

Question

A.  During the priming reactions in glycolysis
B.  During the oxidation and ATP formation reactions in glycolysis
C.  During pyruvate oxidation
D.  During the condensation reaction in the Krebs cycle
E.  During the second oxidation in the Krebs cycle

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

  Gather Content
  What do you already know about cellular respiration and the oxidation of carbon? What other information is related to the question?

  Choose Answer
  Do you have all the information needed to determine at which point glucose is completely oxidized to carbon dioxide?

  Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

E.  During the second oxidation in the Krebs cycle

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine the point at which glucose has been completely broken down to carbon dioxide during cellular respiration.
What type of thinking is required?
        · You are being asked to dissect, or analyze, cellular respiration to determine when the six carbon molecules in glucose have been completely oxidized to carbon dioxide.

  Gather Content
  What do you already know about cellular respiration and the oxidation of carbon? What other information is related to the question?
        · Recall that cellular respiration involves oxidizing carbon in glucose to become carbon dioxide. Consider each stage of cellular respiration: glycolysis, pyruvate oxidation, Krebs cycle, and electron transport. Which of these stages involves the production of carbon dioxide? Why is carbon dioxide produced in the first place?

  Choose Answer
  Do you have all the information needed to determine at which point glucose is completely oxidized to carbon dioxide?
        · Let’s review each step of cellular respiration in order to determine the last point at which carbon dioxide is produced. Glycolysis involves converting a 6-carbon glucose molecule into 2 3-carbon pyruvate molecules. Hopefully it is clear that no carbon dioxide is lost during glycolysis, so no carbon oxidation has occurred.
        · Pyruvate oxidation involves conversion of the 2 3-carbon pyruvate molecules into 2 2-carbon acetyl-CoA molecules. Since matter can’t be created or destroyed, and you have to account for all of the carbon, the only way this can make sense is if 2 carbon dioxide molecules are given off during pyruvate oxidation. Since 2 carbon atoms have been oxidized, that leaves 4 to go in order to account for the 6 six carbons that are oxidized during cellular respiration.
        · If you recall, the Krebs cycle pairs a 2-carbon acetyl-CoA molecule with a 4-carbon oxaloacetate molecule to produce a 6-carbon citrate molecule. However, the 4-carbon oxaloacetate molecule must be continuously regenerated in order to accept more acetyl-CoA molecules. That means that, per citrate molecule from the Krebs cycle, 2 carbon atoms must be oxidized per turn of the Krebs cycle. This involves 2 oxidation events. If you account for the fact that the Krebs cycle must turn twice per glucose molecule, then you know that it is the second oxidation during the Krebs cycle when glucose becomes completely oxidized to carbon dioxide.

  Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Answering this question correctly depended on your ability to analyze cellular respiration for when the 6 carbon atoms in glucose become completely oxidized to carbon dioxide.
        · If you got the correct answer, well done! If you got an incorrect answer, were you able to determine which stages of cellular respiration involved carbon oxidation? Were you able to follow the trail and account for each carbon as it becomes oxidized from glucose? Were you able to determine that the final carbon atoms become oxidized during the Krebs cycle?