Stages of Development

Question 1

Stages of development

Answer 1

• Gamete formation
• Fertilization
• Cleavage
• Gastrulation
• Organogenesis
• Growth

Question 2

Gamete

Answer 2

mature haploid male or female germ cell

Question 3

Egg components

Answer 3

• Components of a normal somatic cell
• Yolk: Provides energy during development
• Polarity

Question 4

Polarity

Answer 4

• Animal pole: contains most of the cytoplasm & nucleus
• Vegetal pole: contains most of the yolk

Question 5

Distribution of yolk in egg

Answer 5

• Isolethical
• Mesolethical
• Telolecthical
• Centrolethical

Question 6

Isolethical

Answer 6

• Very little yolk evenly distributed through egg
• Typical of placental mammals, tunicates, echinoderms, cephalochordates, and molluscs

Question 7

Mesolethical

Answer 7

• Moderate amount of yolk concentrated at vegetal pole
• Typical of amphibians

Question 8

Telolethical

Answer 8

• Abundance of yolk densely concentrated at vegetal pole
• Typical of birds, reptiles, fish, monotremes, some amphibians

Question 9

Centrolethical

Answer 9

• Large centrally located mass of yolk
• Typical of arthropods

Question 10

Developmental patterns associated with amount of yolk

Answer 10

Lots of yolk:
* Direct development
* Telolethical eggs

Little yolk:
* Indirect development
* isolecithal, mesolecithal eggs

Question 11

Fertilization

Answer 11

Gametes unite to form a zygote

Question 12

Cleavage

Answer 12

• Embryo divides repeatedly without growth
• Occurs more easily in cytoplasm than in yolk
• Egg cell becomes many smaller cells called blastomeres

Question 13

Holoblastic cleavage

Answer 13

• Complete and equal division of cells
• Isolethical and mesolethical eggs

Question 14

Meroblastic cleavage

Answer 14

• Restricted to a small area of egg
• Telolethical and centrolethical eggs

Question 15

Cleavage direction

Answer 15

• Radial cleavage
• Spiral cleavage

Question 16

Blastula

Answer 16

• Zygote formed at the end of cleavage
• 1 germ layer

Question 17

Blastocoel

Answer 17

Fluid-filled cavity around which the cells form

Question 18

Gastrulation

Answer 18

Converts blastula into a 2- to 3-layered embryo

Question 19

Gastrula

Answer 19

• Embryo at the end of gastrulation
• 2-3 germ layers

Question 20

Formation of 2nd germ layer

Answer 20

Invagination of blastula

Question 21

Mesoderm

Answer 21

• 3rd germ layer
• Formed from endoderm between endoderm and ectoderm

Question 22

Gut cavity (archenteron/gastrocoel)

Answer 22

Internal pouch formed from invagination of blastula

Question 23

Blastopore

Answer 23

Opening to the gut cavity

Question 24

Ectoderm

Answer 24

Outer layer of cells (lining of the blastocoel)

Question 25

Endoderm

Answer 25

Inner layer of cells (lining of the invagination)

Question 26

Blind gut

Answer 26

Gastrula has one opening

Question 27

Complete gut

Answer 27

Gastrula has two openings

Question 28

Coelom

Answer 28

Cavity completely surrounded by mesoderm

Question 29

Organogenesis

Answer 29

1st event = formation of the nervous system * Formed from the ectoderm 1st functional organ = heart * Formed from the mesoderm Organogenesis takes place during the first 8 weeks

Question 30

Growth

Answer 30

Longest phase in animal development