Chapter 54-Animal Development

Question 1

3 events of fertilization

Answer 1

1. sperm penetration and membrane fusion
2. egg activation
3. fusion of nuclei

Question 2

How does sperm penetration occur

Answer 2

• protective layer of egg eaten away by sperm digestive enzymes located in acrosome
• allows sperm nucleus to enter directly into eggs cytoplasm

Question 3

Egg activation

Answer 3

• dramatic increase in levels of free intracellular Ca2+ ions in egg shortly after sperm makes contact with plasma membrane
• act as second messengers to initiate changes

Question 4

Block to polyspermy

Answer 4

• Rapid transient change in membranc potential

- contical granules remove sperm receptors

Question 5

3 effects of sperm penetration

Answer 5

1. triggers egg to complete meiosis
2. triggers a cytoplasmic rearrangement
3. causes a sharp increase in protein synthesis and metabolic activity in general

Question 6

Fusion of nuclei

Answer 6

haploid sperm and haploid egg nuclei fuse to form diploid nucleus of zygote

Question 7

cell cleavage

Answer 7

-rapid division of zygote into a larger and larger number of smaller and smaller cells forminga solid ball of cells called morula

Question 8

Blastula

Answer 8

forms from morula

-hollow ball of cells

Question 9

Animal pole

Answer 9

portion with no or little yolk

Question 10

vegetal pole

Answer 10

portion with yolk

Question 11

Thing that most affects cleavage pattern of animal embryo

Answer 11

relative amount of nutritive yolk in egg

Question 12

Eggs with little/no yolk

Answer 12

• holoblastic cleavage

- invertebrates, amphibians, mammals

Question 13

Eggs with large amounts of yolk

Answer 13

• meroblastic cleavage

- embryo forms thin cap on yolk

Question 14

Blastocyst composed of..

Answer 14

• trophoblast-outer layer of cells, contributes to placenta
• blastocoel-central fluid filled cavity
• inner cell mass-located at one end, forms developing embryo

Question 15

Gastrulation

Answer 15

• process involving complex series of cell shape changes and cell movements that occurs in blastula
• establishes basic body plan and creates 3 primary germ layers (ectoderm-exterior, mesoderm-middle, endoderm-inner)

Question 16

Gastrulation in mammals

Answer 16

• embryo develops from inner cell mass

- embryo gastrulates as if it was sitting in a ball of yolk

Question 17

Extraembryonic membranes

Answer 17

• amnion, chorion, yolk sac, allantois
• only in adaptation to life on dry land
• nourish and protects developing embryo

Question 18

Amniotic membrane

Answer 18

-encloses amniotic fluid

Question 19

Chorion

Answer 19

-contributes to placenta in mammals

Question 20

Yolk sac

Answer 20

-food source in bird embryos

Question 21

Allantois

Answer 21

• unites with chorion in birds, forming a structure used for gas exchange
• in mammals, contributes blood vessels to the developing umbilical cord

Question 22

organogenesis

Answer 22

• formation of organs in their proper locations

- follows rapidly on heels of gastrulation

Question 23

Notochord

Answer 23

• forms from mesoderm
• region of dorsal ectodermal cells situated above notochord thickens to form the neural plate
• cells of the neural plate fold together to form the neural tube
• will become brain and spinal chord