MCAT Biology Question 33: Answer and Explanation
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Question: 33
3. From which of the following layers does the notochord form?
- A. Ectoderm
- B. Mesoderm
- C. Endoderm
- D. Archenteron
Correct Answer: B
Explanation:
A rod of mesodermal cells called the notochord develops along the longitudinal axis just under the dorsal layer of ectoderm. Through inductive effects from the notochord, the overlying ectoderm starts bending inward and forms a groove on the dorsal surface of the embryo. The dorsal ectoderm will eventually pinch off and develop into the spinal cord and brain. While the neural tube forms from ectoderm, the notochord itself is mesodermal.