Cardiac muscle cells are connected by special junctions called intercalated discs. Intercalated discs provide strength between cells of tissues which exhibit high mechanical stress, strong flexible connections between tissue cells, and electrical excitability between the cells. Using this information, which junctions are present in intercalated discs?

Question

A.  Tight, plasmodesmata, and adherens
B.  Tight, plasmodesmata, and desmosomes
C.  Gap, adherens, and desmosomes
D.  Gap, desmosomes, and hemidesmosomes
E.  Adherens, tight, and gap

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 know about junctions? 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.  Gap, adherens, and desmosomes

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the types of junctions found in an intercalated disk.
· What type of thinking is required?
        o You are being asked to apply your knowledge of the attributes found in each junction to predict which would be present in an intercalated disk.
· What key words does the question contain and what do they mean?
        o Junctions called intercalated disks – junctions are structures found between cells.  They can be adhesive – holding cells together, or communicating – allowing cells to send electrical impulses or compounds between adjacent cells.

Gather Content
· What do you know about junctions? How does it relate to the question?
        o There are several classes of junctions with different functions.
Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Plasmodesmata are found in plants and would not be in heart tissue.
        o The heart muscle cells do not need to prevent molecules from moving between the cells, so they would not need gap junctions.
        o Heart cells do not need to migrate, so they would not require hemidesmosomes.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Because heart muscle cells need to contract and relax constantly for the life of the organism, the cells must be connected by strong flexible connections capable of withstanding high mechanical stress.  Desmosomes and adherens junctions are capable of these two functions respectively.  In addition, once a region of the heart starts to contract, that electrical impulse must move through the wall of the heart so all of the muscle beats in a smooth rhythm.  Gap junctions allow signaling molecules to move from one heart muscle cell to the next carrying this message and keeping the heart in rhythm.

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?
        o This question asked you to apply the definitions of different types of junctions to predict which would be present in the intercalated disks holding heart muscle cells together. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you have trouble recalling the definitions of the different cellular junctions?  Did you realize that there were three different junctions being described in the question?