You a given a plant tissue in lab and asked to determine if the tissue is a source or a sink. Microscopic analysis reveals an abundance of colorless parenchyma cells with plastids. Only one biochemical test reacts positively with your sample. In the presence of iodine, the plastids turn a dark purplish color. Based on this information you determine your sample is

Question

A.  a source because your sample is rich in carbohydrates.
B.  a source because your sample contains plastids.
C.  a sink because your sample is rich in carbohydrates.
D.  both a source and sink because it contains both plastids and carbohydrates.

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 the function of a sink in a plant? 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.  a sink because your sample is rich in carbohydrates.

Clarify Question
What is the key concept addressed by the question?
        · The key concept is that a sink can be differentiated by the presence of stored carbohydrates.
What type of thinking is required?
        · You are being asked to take what you already know apply it to the analysis of unknown tissue to determine whether the tissue is a source or a sink.
What key words does the question contain and what do they mean?
        · Source, which is the part of the plant that is photosynthetic.
        · Sink, which is the part of the plant that uses or stores carbohydrates.
        · Iodine, can be used as an indicator for starch.

Gather Content
What do you already know about the function of a sink in a plant? How does it relate to the question?
        · Colorless tissue is not photosynthetic.
        · The product of photosynthesis is glucose.
        · Glucose is stored by plants as starch.
        · A positive iodine test for starch turns blue black in color.

Consider Possibilities
What other information is related to the question? Which information is most useful?
        · Content specific to key concept.

Choose Answer
Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        · Sources are photosynthetic, so they are green in color. They would not contain colorless plastids.

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 apply what you know about sources and sinks to a sample of unknown origin. Answering this question correctly depended on your ability to use these ideas about sources and sinks in a new situation¼ If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you remember that sinks are sites of carbohydrate use and storage, or that iodine indicates starch by turning blue-black? Did you have trouble extending these concepts to determine the correct answer?