If you exposed a C4 plant to 14CO2 in the light, which would be the first organic molecule labeled with 14C?

Question

A.  oxaloacetate
B.  malate
C.  pyruvate
D.  phosphoenolpyruvate (PEP)

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 how carbon fixation in C3, C4, and CAM plants? How does photosynthesis differ in these plants? What other information is related to the question?

  Choose AnswerDo you have all necessary information to determine which organic molecule would be first to be labeled with 14C in a C4 plant?

  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

A.  oxaloacetate

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine which organic molecule would be the first to be labeled with 14C in a C4 plant.
What type of thinking is required?
       · You are being asked to dissect, or analyze, which molecule in a C4 plant would be labeled with 14C first.

  Gather Content
What do you already know about how carbon fixation in C3, C4, and CAM plants? How does photosynthesis differ in these plants? What other information is related to the question?
        · Recall that plants are evolutionarily adapted to particular climates and environments. Part of a plant’s ability to adapt to an environment has to do with how and where it metabolizes carbon, and what happens to the machinery that fixes carbon when conditions are not optimal. It also has to do with the plant’s ability to balance intake of carbon dioxide with loss of water in hot, dry environments. C4 and CAM plants essentially use two strategies to address environmental stressors; separation of light reactions and carbon fixation by space and by time.

  Choose Answer
Do you have all necessary information to determine which organic molecule would be first to be labeled with 14C in a C4 plant?
        · C4 and CAM plants use different strategies to deal with hot temperatures and water loss issue during the day. C4 plants acquire carbon dioxide and transport it in a different form to a separate location before making it available for the Calvin cycle. CAM plants acquire carbon dioxide at night when it is cooler and water loss is less likely to happen and store it until daytime when photosynthesis can take place.
        · Since we are talking about a C4 plant here, let’s focus on how that plant takes in carbon dioxide in its adverse environment. Recall that a C4 plant first locks carbon dioxide onto a three-carbon molecule to form a four-carbon oxaloacetate molecule. Thus, a carbon dioxide molecule labeled with 14C would first be incorporated into oxaloacetate before any of the other molecules.

  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 which molecule would be the first to be labeled with 14C in a C4 plant.
        · If you got the correct answer, well done! If you got an incorrect answer, were you able to identify which molecules receive carbon dioxide in C4 plants? Did you remember that oxaloacetate is a four-carbon molecule? Were you able to recognize that 14C from the carbon dioxide must end up in oxaloacetate because it is the first molecule formed during carbon fixation in C4 plants?