Section Test:Embryogenesis

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Topics Covered

This Section Test deals with the basic MCAT embryogenesis topics. How a zygote develops into a multicellular entity, what the different cell layers are, and the processes of differentiation. See Embryogenesis for the article relating to this section test.

Section Test

1. During cleavage the single large cell of the zygote is converted into a?

multicellular embryo consisting of smaller cells called blastomeres
→ While all the answers are correct in a sense, the cleavage phase specifically ends when the divisions have ended and a group of blastomeres are left, all the other answers occur as part of later stages of development.
three-layered embryo called a gastrula
multicellular embryo with a blastopore and an archenteron
fetus

2. In examining a frog blastula, it is found to be made up of ~60 cells, how many cleavages have taken place since the zygote stage?

2
4
6
8
→ During cleavage, each cell in the embryo splits into two, thus beginning at the zygote the number of cells increases as 1, 2, 4, 8, 16, 32, 64, which works out to be about 6 divisions.

3. One difference between the blastula and gastrula stages of development is that?

cells in the blastula are more differentiated than those in the gastrula
there are more cells in a blastula stage than in the gastrula stage
there are more cell layers in the blastula stage than in the gastrula stage
the blastula is made of a layer of cells with a hollow inside while the gastrula is also hollow but has an opening
→ The blastula is the result of the morula from the cleavage phase rearranging to become hollow. Given time a region of cells cave back inwards creating a second layer inside with a cavity. This two layered mass of cells with a cavity and opening to the outside is known as the gastrula.

4. Which one of the following describes the correct sequence of stages during embryogenesis?

cleavage, blastula formation, gastrulation
cleavage, gastrulation, blastula formation
blastula formation, gastrulation, cleavage
gastrulation, cleavage, blastula formation
→ The correct order of events starting from a zygote is cleavage, blastula formation, followed by gastrulation. These are basically the events needed to go from one large cell, to many smaller cells, to a hallow ball of cells.

5. The brain of humans develops from?

endoderm
mesoderm
ectoderm
both ectoderm and endoderm
→ During neurolation, a small group of ectoderm cells pinch off to form the neuronal tube, which then differentiate to form the brain and spinal cord.

6. During gastrulation, the primitive __________ forms.

eye
gut
nervous system
heart
→ the inner cavity of the gastrula, known as the archenteron, becomes the inside of the gut.

7. Drugs, alcohol, and radiation can disrupt human embryonic development. These exposures have the most severe effects on the fetus if they occur during the first three months of gestation because at this time?

substances can most easily enter the embryo through the placenta
the embryo has not yet been implanted in the wall of the uterus
the mother's hormone levels are highest
the most drastic and rapid changes are occurring in the embryo
→ Because all subsequent developmental changes rely on the first initial divisions, any mutations can drastically alter later events.

8. What is the embryonic source of the skeleton, muscles, and circulatory system?

mesoderm
ectoderm
endoderm
all three germ layers
→ The mesoderm develops into most of the inner parts of the body, excluding some organs and the digestive system which come from the endoderm.

9. If there was an abnormality in the lining of the bladder in the embryo, this would arise from the

ectoderm
endoderm
mesoderm
blastomere
→ the endoderm develops into the inner lining of the digestive system, which include the bladder.

10. A mutation in the embryonic mesoderm could effect all of the following organs/tissues except?

heart
epidermis
blood vessels
connective Tissue
→ With the exception of the epidermis, which comes from the ectoderm, all the remaining answers are derived from the mesoderm layer.

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