A lab technician is preparing to dispose of a rat and a frog that were euthanized earlier in the day for a scientific study. Although the two animals died at the same time, the rat has rigor mortis while the frog does not yet show any signs of it. What is the best explanation for this time difference in the onset of rigor mortis?

Question

A.  The rat has higher concentrations of myoglobin in its muscles than the frog.
B.  All the frog's muscles are fast-twitch muscles.
C.  The rat's muscles have a greater density of myofilaments than the frog's muscles.
D.  The frog has lower concentrations of glycogen in its muscles than the rat.
E.  The rat is able to synthesize more ATP than the frog.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you know about rigor mortis? What other information is related to the question?

Choose Answer
· Given what you now know, what information 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 rat's muscles have a greater density of myofilaments than the frog's muscles.

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about rigor mortis.
· What type of thinking is required?
        o You are being asked to apply your knowledge about rigor mortis.

Gather Content
· What do you know about rigor mortis? What other information is related to the question?
        o In death, the cell can no longer produce ATP, and therefore the cross-bridge cycle cannot be broken—causing the muscle stiffness of death called rigor mortis. A living cell, however, always has enough ATP to allow the myosin heads to detach from actin. It takes several minutes for the cells to use up their supplies of ATP in the absence of oxygen and typically a few hours for rigor mortis to occur. Once established rigor mortis will persist for about 12 hours.

Choose Answer
· Given what you now know, what information is most likely to produce the correct answer?
        o Without ATP, the myosin cross-bridges in the muscles will not detach from the actin filaments and the muscles enter rigor mortis. A reduced ability to synthesize ATP or a faster rate of using it up will speed up the rate at which different muscles enter into rigor mortis. If the rat's muscles have a greater density of myofilaments than the frog's muscles, they will have more cross bridges to break and will remain in rigor mortis longer. If the rat had more myoglobin, glycogen, or ATP than the frog then it would have more of a delay in rigor mortis occurring, which is the opposite of what was observed.

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 your knowledge about rigor mortis. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you think that more myoglobin, glycogen, or ATP would increase the rate of rigor mortis? Did you think that rigor mortis had already ended in the frog?