A plant researcher wants to construct a synthetic cellulose fiber from 20 glucose molecules. How many molecules of CO2 and glyceraldehyde-3-phosphate are needed to construct the fiber?

Question

A.  20, 40
B.  120, 60
C.  120, 40
D.  20, 60
E.  120, 120

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 the Calvin cycle, carbon dioxide, and glyceraldehyde-3-phosphate? What other information is related to the question?

  Choose Answer
Do you have all the information needed to determine the likely outcome?

  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

C.  120, 40

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to decipher how many molecules of carbon dioxide and glyceraldehyde-3-phosphate are needed to construct a cellulose fiber comprised of 20 glucose molecules.
What type of thinking is required?
        · You are being asked to dissect, or analyze, a synthetic cellulose fiber that is 20 glucose molecules long to determine how many molecules of carbon dioxide and glyceraldehyde-3-phosphate are needed.

  Gather Content
What do you already know about the Calvin cycle, carbon dioxide, and glyceraldehyde-3-phosphate? What other information is related to the question?
        · Recall that the biological function of the Calvin cycle is to fix carbon from the atmosphere into an organic molecule. The Calvin cycle uses ATP and NADPH produced during the light reactions to fix inorganic carbon into an organic form within the stroma of chloroplasts. One turn of the Calvin cycle is required for each carbon dioxide molecule that is fixed by the enzyme rubisco.
        · Remember that the Calvin cycle is an iterative process, meaning that carbon dioxide is accepted, molecules are transformed, and excess carbohydrate in the form of glyceraldehyde-3-phosphate is harvested. How many carbons make up glyceraldehyde-3-phosphate, and how many turns of the Calvin cycle would be required to produce this molecule?

  Choose Answer
Do you have all the information needed to determine the likely outcome?
        · Remember that, during the Calvin cycle,RuBP binds to a single carbon dioxide molecule and produces a six-carbon molecule that is then converted into two three-carbon molecules of 3-phosphoglycerate. Each of these molecules is subsequently converted into two three-carbon glyceraldehyde 3-phosphate molecules. A complex series of chemical reactions is needed to regenerate RuBP; however excess glyceraldehyde 3-phosphate molecules can be harvested and used to make a six-carbon glucose molecule.
        · If you understand how many carbons make up glyceraldehyde-3-phosphate and glucose, the rest should be fairly straightforward math. A synthetic cellulose fiber that contains 20 glucose molecules would contain six times that number in carbon atoms because glucose has six carbons in its structure, meaning 120 molecules of carbon dioxide would be required to make the fiber.On the other hand, glyceraldehyde-3-phosphate contains three carbons and so would require one third the total number of carbon atoms, which in this case is 40.

  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 the Calvin cycle to determine how many carbon dioxide and glyceraldehyde 3-phosphate molecules would be needed to make a synthetic cellulose fiber that contained 20 glucose molecules.
        · If you got the correct answer, well done! If you got an incorrect answer, did you recall how many carbon dioxide molecules the Calvin cycle can fix per turn? Did you remember how many carbon atoms are in a glyceraldehyde 3-phosphate molecule, and how many of these are required to make one glucose molecule? Were you able to calculate the total number of carbon dioxide and glyceraldehyde-3-phosphate molecules based on this information?