To your chagrin, you and your labmate have discovered that you both labeled your petri dishes “A”, “B”, and “C”. How can you distinguish your sea urchin gastrula embryos from her frog gastrula embryos?
A. Unlike frogs, sea urchins are deuterostomes which form the anus first and the mouth second.
B. Sea urchin cells migrate inside to form the archenteron, whereas in frogs proliferation of dividing cells from the dorsal lip populate the inside of the embryo.
C. Sea urchins have relatively yolk-poor eggs with similar animal and vegetal poles, whereas frogs have large amounts of yolk distinguishing the vegetal pole from the animal pole.
D. Frogs have an animal pole and vegetal pole, whereas urchins have only a vegetal pole.
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 eggs? 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?
C. Sea urchins have relatively yolk-poor eggs with similar animal and vegetal poles, whereas frogs have large amounts of yolk distinguishing the vegetal pole from the animal pole.
Clarify Question
What is the key concept addressed by the question?
· This question is asking you to differentiate the embryos of two different species based on their morphology.
What type of thinking is required?
· Analyze level:
o This is an analyze question because you have to break the embryos of sea urchins and frogs into their component pieces to understand how they differ.
Gather Content
What do you already know about eggs? What other information is related to the question?
· Frogs, as members of the Phylum Chordata, and sea urchins, as members of the Phylum Echinodermata, are both deuterostomes.
· Deuterostomes and protostomes are the two major embryological pathways into which animal species can be divided.
· Deuterostomes do not form their mouth from the first embryological opening, while protostomes do form their mouth from the first embryological opening.
· Animal species differ in the amount of yolk that is deposited in eggs. This can be used to distinguish the embryos of different species.
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
· Frogs and sea urchins are both deuterstomes, and the differences between protostomes and deuterstomes are not visually apparent at gastrulation, so this answer can be disregarded.
· Both sea urchins and frogs have animal and vegetal poles in their embryos, so differentiating them does not involve the lack of either pole.
· The yolk content of sea urchin and frog embryos differs significantly, and this can be used to distinguish one from the other. Sea urchin eggs have little yolk, while frog eggs have so much yolk that it displaces the animal pole.
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?
· Analyze level:
o Answering this question correctly depended not only on distinguishing between sea urchin and frog embryos, but on your ability to break down, or analyze, the differences that are present in the eggs of these creatures. If you got an incorrect answer, did you remember that components of sea urchin eggs include little yolk, or that the yolk in frog eggs is proportionally much greater? Did you have trouble breaking down the differences in egg composition to determine the correct answer?
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