When legumes with nitrogen-fixation nodules are given chemical fertilizers with high nitrogen concentrations, they abandon support of the nodules and end the symbiosis. Why?

Question

A.  The mineral nutrients inhibit nitrogenase activity.
B.  Nitrogen gas is no longer available in the soil.
C.  The plant can conserve valuable energy sources by terminating the symbiotic relationship.
D.  The dissolved chemical nutrients are toxic to Rhizobium bacteria.
E.  Dissolved nitrogen uncurls the root hairs, releasing the nodule.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you already know about nitrogen-fixation nodules? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

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.  The plant can conserve valuable energy sources by terminating the symbiotic relationship.


Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the benefit of nitrogen-fixation nodules.
· What type of thinking is required?
        o You are being asked to take what you already know and apply it to  a situation in which the environment of a plant has changed.
· What key words does the question contain and what do they mean?
        o Legume, which is a plant such as a bean or a pea that puts its seeds in a long case.
        o Nitrogen-fixation nodule, which is a structure that contains nitrogen-fixing bacteria.
        o Symbiosis, which refers to two organisms that live together.

Gather Content
· What do you already know about nitrogen-fixation nodules? How does it relate to the question?
        o Legumes form nodules when they are in nitrogen-poor soil.
        o Nodules contain nitrogen-fixing bacteria that take unusable atmospheric nitrogen and convert it into a usable form.
        o This helps to mitigate the nitrogen-poor environment.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o The only change is that nitrogen is more freely available. Since this has occurred, the plant no longer requires the nitrogen-fixing bacteria. These bacteria are kept a cost, which is the oxygen and carbohydrates that they require. By no longer supported the nodules, the plant conserves resources.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
       o To answer this question, you must connect the role of the nitrogen-fixing bacteria in the nodules with the nitrogen that they make available. Since nitrogen is newly added to the soil in the fertilizer and therefore readily available, the plant no longer needs the nodules.

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?

· Apply level:
       o This question asked you to understand the main reason that it is beneficial to a plant to retain nodules. Answering this question correctly depended on your ability to use the function of these nodules in a new situation. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you remember that nodules function to make nitrogen available in nitrogen-poor soils, or that this would no longer be necessary if nitrogen is readily available? Did you have trouble extending the role of nodules to determine the correct answer?