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MCAT Biology Question — Relevant Connection

Which of the following correctly indicates the order and relevant connection between the listed terms:

I. Zygote → Blastula → Gastrula
II. Morula → Inner Cell Mass → Placenta
III. Gastrula → Ectoderm → Neural Tissue


A) I only
B) I and II only
C) I and III only
D) II and III only



When the embro begins forming, it passes through four general stages: Zygote, Morula, Blastula, Gastrula. Thus (I) gets the order of the listed terms correct (although it skips the morula stage). After the gastrula develops, organogenesis follows. In that process, organ systems develop from the three primary germ layers: endoderm, mesoderm, ectoderm. The ectoderm gives rise to epidermis and the tissues of the nervous system. Thus (III) indicates the correct connections.

(II) is false because it lists the placenta coming from the inner cell mass. The inner cell mass develops into the embryo. It is the trophoblasts surrounding the inner cell mass that become the placenta.

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