How would an earthworm stretch its body to reach a patch of dirt after crossing a hot sidewalk?

Question

A.  Contraction of the circular muscles
B.  Contraction of the longitudinal muscles
C.  Relaxing the chaetae (setae)
D.  Pulling on the chaetae (setae)

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 earthworm locomotion?

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

A.  Contraction of the circular muscles

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses earthworm locomotion.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.

Gather Content
· What do you already know about earthworm locomotion?
        o The basic annelid body plan is a tube within a tube.
        o The coelomic fluid creates a hydrostatic skeleton that gives each segment rigidity, like an inflated balloon.
        o Annelids move by contraction of the circular and longitudinal muscles against the hydrostatic skeleton.
        o When circular muscles are contracted around a segment, the segment decreases in diameter, so the coelomic fluid causes the segment to elongate.
        o When longitudinal muscles contract, the segment shortens, so the coelomic fluid causes the segment to increase in diameter.
        o Alternating these contractions and confining them to only some segments allows the worms to move in complex ways.
        o In most annelid groups, each segment possesses bristles of chitin called chaetae or setae. By extending the chaetae in some segments so that they protrude into the substrate and retracting them in other segments, the worm avoids slipping.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o To stretch or elongate the body, an annelid contracts the circular muscles around the segment. This causes the segment to get longer.

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 The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that the two sets of muscles in an earthworm – circular and longitudinal – allow it to transform its body in different ways?