Test 3 Unit 4

Question 1

Describe the different steps of cleavage.

Answer 1

1. Cleavage divisions of Zygote into 2 cells, 4 cells,… and more
2. Morula: solid ball/layer of cells
3. Divisions continue, the ball/layer hollows out
4. Blastula: hollow ball of blastomeres (cells)

Question 2

Describe the components of the blastula.

Answer 2

• Blastula: hollow ball of blastomeres
• Blastomeres: cells of the blastula
• Blastocoel: fluid-filled cavity

Question 3

What are the different tissues/structures of the gastrula?

Answer 3

Ectoderm, endoderm, mesoderm, archenteron, blastopore

Question 4

What will the different tissues/structures of the gastrula lead to in the formation of organs?

Answer 4

Ectoderm: skin and nervous system
Endoderm: digestive and respiratory tracts
Mesoderm: muscles, bones and circulatory system
Archenteron: gut
Blastopore: mouth/anus

Question 5

Explain cell divisions and gastrulation in amphibian eggs.

Answer 5

1. Fertilization of the egg inside the animal pole
2. Rotation of the pigment layer towards site of fertilization
3. 1st cytoplasmic division ⊥ to grey crescent
4. Many cleavage divisions
5. Gastrulation: invagination of the blastocoel
6. Animal half encloses the vegetal half.

Question 6

Explain cell divisions and gastrulation in bird eggs.

Answer 6

• Yolk occupies almost the entire volume*
  1. Cleavage divisions form a blastodisc at the top of the yolk.
  2. Blastodics separates into 2: epiblast and hypoblast
  3. epiblast cells migrate towards middle and cells migrate downward and form the mesoderm
  4. Mesoderm splits in 2, forms coelum (fluid-filled cavity)
  5. Cells migrate towards the outside = Gastrulation
  6. Archenteron (interior of digestive cavity) is formed

Question 7

What is the main difference(s) between amphibian and bird cleavage and gastrulation?

Answer 7

Cleavage: amphibian is 1/2 yolk (vegatal) 1/2 none, and bird id full yolk
Gastrulation: bird has opposite migration where ectoderm and mesoderm move downward around the sides of the endoderm and will enclose the coelum.

Question 8

How do transcription factors regulate the differentiation of stem cells?

Answer 8

the primitive layers develop into organs with transcription factors. Under genetic control, some cells of primitive layers differentiate into the wanted organ.

Question 9

Give an example of the regulation of the differentiation of stem cells by transcription factors?

Answer 9

Somite → Myoblast → Skeletal muscle cells

Somites are blocks of mesoderm cells in mammals that form along both sides of the notochord and they can differentiate into skeletal muscle cells with the transcription factors MyoD (determination), myogenin and MEF (differentiation).