If you tagged organic carbon inside a chloroplast with a fluorescent label, the location most likely to have a high concentration of labeled carbon would be in the

Question

A.  Stroma
B.  Thylakoid membrane
C.  Between the outer and inner membranes
D.  Inside the thylakoid

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 photosynthesis and where these processes take place in chloroplasts? What other information is related to the question?

  Choose Answer
Do you have all necessary information to determine the most likely location?

  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.  Stroma

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine where in a plant cell a high concentration of labeled carbon would be if you tagged organic carbon.
What type of thinking is required?
        · You are being asked to break down, or analyze, where in a chloroplast you would find a high concentration of labeled organic carbon.

  Gather Content
What do you already know about photosynthesis and where these processes take place in chloroplasts? What other information is related to the question?
        · Recall that photosynthesis is comprised of the light reactions and the Calvin cycle, both of which occur inside chloroplasts. During the light reactions, which take place in the thylakoid membranes, energy from the sun is captured using molecules like chlorophyll to remove electrons from water, excite them to a higher energy level, and to use redox reactions in order to produce ATP and NADPH.These products are then exported outside the thylakoid to the stroma where the Calvin cycle then uses ATP and NADPH produced during the light reactions to fix inorganic carbon into inorganic form within chloroplasts.
        · Remember that chloroplasts are comprised of various compartments by the outer and inner chloroplast membranes as well as the thylakoid membrane. Given what the information provided in the question, where do you think the most labeled organic carbon might be located?

  Choose Answer
Do you have all necessary information to determine the most likely location?
        · Recall that ATP and NADPH produced by the light reactions in the thylakoid membrane are exported to the stroma, which is the location of the Calvin cycle and also inorganic carbon is fixed from the atmosphere into an organic molecular form (e.g carbohydrate).
        · Because the thylakoid membrane is involved in the light reactions, it is unlikely to be the location for labeled carbon in this question. Likewise, we know that it can’t be inside the thylakoid because no carbon fixation takes place there. Considering that the stroma is where carbon fixation takes place, it is also the most likely location for labeled carbon in the chloroplast.

  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 what you know about where in chloroplasts the light reactions and the Calvin cycle take place to determine the most likely location of labeled organic carbon.
        · If you got the correct answer, good job! If you got an incorrect answer, did you recall that photosynthesis is made up of the light reactions and the Calvin cycle, and that only the Calvin cycle is involved with carbon fixation? Were you able to remember that the light reactions are associated with the thylakoid membranes and therefore could be eliminated as possibilities? Were you able to determine that, because the Calvin cycle is located in the stroma and the purpose of the Calvin cycle is to fix carbon, the stroma must be the most likely location?