Chapter 1

Question 1

Match these descriptions of cleavage along planes to the name of the plane.
1. Divides an animal into its dorsal and ventral sides
2. Divides an animal into its anterior and posterior
3. Divides an animal into its left and right sides

A. Mid-sagittal
B. Transverse plane/cross-section
C. Coronal/Horizontal

Answer 1

1C
2B
3A

Question 2

What marks the start of organogenesis?

Answer 2

Neurulation

Question 3

Name the key stages in amphibian embryonic development.

Answer 3

Egg, Morula, Blastula, Gastrula, Neurula

Question 4

What are some key features of the following stages of amphibian embryonic development?
Morula, Blastula, Gastrula, Neurula

Answer 4

Morula: The beginning of cleavage
Blastula: Cells dividing asynchronously
Gastrula: Cell has blastocoel and blastopore, beginning to form germ layers from invagination, the formation of germ layers marks the end of gastrulation
Neurula: Neurulation, gastrulation is done

Question 5

What is the difference between holoblastic and meroblastic cleavage?

Answer 5

In holoblastic cleavage, the yolk is thin and evenly distributed and divides along with the cells.
In meroblastic cleavage, the yolk is too thick to divide with the cells, thus there forms a clear separation between the yolk and the dividing cells in the developing embryo.

Question 6

What is a key difference during gastrulation between a human and amphibian embryo?

Answer 6

In amphibians, the formation of the blastopore and the invagination of cells marks gastrulation.
In humans, it’s the formation of the primitive streak and the node

Question 7

What is the function of the notochord?

Answer 7

It dictates ectoderm’s formation into the neural tube and is formed from the mesoderm during gastrulation.

Question 8

What are the two basic cell types in the embryo? What germ layers do they originate from?

Answer 8

Epithelial cells: Attached in a sheet
Mesenchymal cells: individualized, can be motile

Question 9

Can epithelial cells transition to mesenchymal? What about the reverse?

Answer 9

Both are possible. EMT or MET. Gene controlled.

Question 10

What is a difference between early cell division and cell division during gastrulation?

Answer 10

Early cell division is fast and synchronous, cell division during gastrulation is asynchronous and slower

Question 11

What is invagination?

Answer 11

The infolding of an epithelium of cells

Question 12

What is involution?

Answer 12

The inward movement of an expanding outer layer so it spreads over the internal surface of the rest of the external cells

Question 13

What is ingression?

Answer 13

Individual cells from the surface become mesenchymal and move to the cells interior.

Question 14

What is delamination?

Answer 14

A cellular sheet splits into two parallel sheets. It differs from ingression as it forms a new epithelial sheet instead of just mesenchymal cells.

Question 15

What is epiboly?

Answer 15

Epithelial sheets spreading as a unit to enclose deeper layers of the embryo.

Question 16

What is convergent extension?

Answer 16

Movement of lateral cells of germ layers to the midline, leads to a convergence of those cells along the medial to lateral axis and an extension anteriorally and posteriorally.