Chapter 03 Formation of Germ Layers and Early Tissue and Organ Differentiation

Chapter 03  Formation of Germ Layers and Early Tissue and Organ Differentiation

Complete Chapter Questions And Answers
 

Sample Questions

MULTIPLE CHOICE

Directions: Each group of questions below consists of a numbered list of descriptive words or phrases accompanied by a diagram with certain parts indicated by letters and a list of lettered headings. For each numbered word or phrase, select the lettered part or heading that matches it correctly and then insert the letter in the space to the right of the appropriate number. Sometimes more than one numbered word or phrase may be correctly matched to the same lettered part or heading.

1.
________ Notochordal process
a.
A
b.
B
c.
C
d.
D
e.
E

ANS: B
The notochordal process is a rod-shaped structure composed of cells derived from the primitive node of the primitive streak. It is the primordium of the notochord, a cellular structure that defines the primordial axis of the embryo.

2.
________ Site of the prechordal plate
a.
A
b.
B
c.
C
d.
D
e.
E

ANS: A
The site of the prechordal plate is indicated in the drawing by a dotted oval to indicate that it is not visible from the dorsal surface of the embryonic disc. The prechordal plate is a circular area of thickened embryonic endoderm in the cranial part of the roof of the umbilical vesicle. The prechordal plate, together with the overlying embryonic ectoderm, later constitutes the oropharyngeal membrane.

3.
________ Gives rise to most of the embryonic mesoderm
a.
A
b.
B
c.
C
d.
D
e.
E

ANS: D
The primitive streak, a linear band of epiblast, gives rise to mesoderm mainly during the third week. The mesoderm extends laterally and becomes continuous with the extraembryonic mesoderm on the amnion and umbilical vesicle.

4.
________ Primitive pit

ANS: C
The primitive pit is a depression in the primitive node at the cranial end of the primitive streak. It extends into the notochordal process and forms the notochordal canal. Thus, it is the entrance to the notochordal canal. The pit later forms the opening of the neurenteric canal, which temporarily connects the amniotic cavity with the umbilical vesicle.

5. ________ Aggregation of angioblasts
A.
Allantois
B.
Primitive streak
C.
Notochord
D.
Blood island
E.
Neural plate

ANS: D
Splanchnic mesenchymal cells known as angioblasts aggregate to form isolated masses called blood islands, which develop into vascular endothelium and primordial blood cells. Blood islands form first on the umbilical vesicle, chorion, allantois, and connecting stalk, but they develop in the embryo about 2 days later.