The ATP generated from cellular respiration is not sufficient to drive the Calvin cycle in plants, even if appropriate levels of NADPH and CO2 are present. Why not?

Question

A.  Plants do not undergo cellular respiration
B.  Breaking down sugar to provide the energy needed to synthesize sugar would be a futile cycle
C.  The Calvin cycle requires more ATP than can possibly be made from cellular respiration
D.  Cellular respiration and photosynthesis do not happen in the same cells in plants

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, photosynthesis, and cellular respiration in plants? What other information is related to the question?

  Choose Answer Do you have all the information need to determine why ATP from cellular respiration needs to be supplemented with ATP from the light reactions?

  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

B.  Breaking down sugar to provide the energy needed to synthesize sugar would be a futile cycle

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine why ATP generated during cellular respiration is insufficient to drive the Calvin cycle in plants even when there is plenty of NADPH and CO2.
What type of thinking is required?
        · You are being asked to break down possible scenarios, or analyze, why there isn’t enough ATP produced from cellular respiration to drive the Calvin cycle even when NADPH and carbon dioxide are not limited.

  Gather Content
What do you already know about the Calvin cycle, photosynthesis, and cellular respiration in plants? What other information is related to the question?
        · Recall that photosynthesis is comprised of the light reactions and the Calvin cycle. ATP and NADPH, the main products of the light reactions, provide the energy and reducing power needed during the Calvin cycle to fix carbon dioxide from the atmosphere into an organic form.
        · Have you ever wondered how plants continue to operate during the night when the light reactions are not producing ATP and NADPH? Remember that plants also contain mitochondria in addition to chloroplasts; that means they are able to metabolize the sugars they produce during photosynthesis to produce ATP needed to operate a wide variety of cellular processes.
        · How efficient do you think it would be for a plant to operate the Calvin cycle using only ATP from cellular respiration?

  Choose Answer Do you have all the information need to determine why ATP from cellular respiration needs to be supplemented with ATP from the light reactions?
        · Let’s approach answering this question logically. Plants possess mitochondria, so the answer that says plants don’t undergo cellular respiration is clearly incorrect. And the fact that mitochondria exist in the same cell at the same time as chloroplasts indicates that answer is also not an option.
        · The Calvin cycle and the process of fixing carbon into an organic form from atmospheric carbon is an inherently energy-intensive process; it simply takes a great deal of energy to overcome entropy and create the more ordered organic molecules in the Calvin cycle. And while cellular respiration does produce ATP, it doesn’t produce enough to overcome the inherent energy inefficiency, nor does cellular respiration produce the NADPH needed during to fix carbon.
        · It’s not that cellular respiration can’t produce enough ATP, it’s that there wouldn’t be enough ATP production to cover the plant cell’s energy costs and still have enough left over to make excess carbohydrate. Thus, breaking down the sugar needed to provide the energy needed to make more sugar would be a zero sum proposition.
  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 why ATP produced during plant cellular respiration is insufficient to drive the Calvin cycle even when NADPH and carbon dioxide levels are sufficient.
        · If you got the correct answer, well done! If you got an incorrect answer, did you recall that plant cells contain mitochondria and chloroplasts? Were you able to determine why ATP from the light reactions and cellular respiration are needed to meet plant cell energy costs? Were you able to infer how inherently inefficient making sugar to break it down for energy to make sugar again would be?