MCAT Biology – Germ Layers

The lining of the digestive tract and the respiratory tract develops from which germ layer?

I. Endoderm
II. Mesoderm
III. Ectoderm

a) I only

b) II only

c) III only

d) I and II

Explanation
The lining of the digestive tract and the respiratory tract develops from the endoderm. As a rule of thumb for the MCAT, think of the fetus developing from a tube. Skin and nervous systems develop from ectoderm (outside of tube), digestive tract and respiratory tract from endoderm (inside of tube), and cardiovascular, skeletal, and muscle tissues develop from mesoderm (in-between outside and inside of tube). On MCAT questions, tissues will almost always develop from one germ-layer only.

I. Endoderm
II. Mesoderm
III. Ectoderm

a) I only, correct.

b) II only, incorrect.

c) III only, incorrect.

d) I and II, incorrect.

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