Lecture 4 - metazoan development

Question 1

what are the 3 types of ova

Answer 1

1) isolethical - evenly distributed yolk
2) telolethical - conc of yolk in vegetal pole
3) centrolethical - conc of yolk in middle

Question 2

what type of fertilisation to sea urchins have and why are they useful?

Answer 2

external - used as a model species for looking at development

Question 3

describe an acrosomal reaction

Answer 3

• sperm touches egg membrane causes series of reactions:
• sodium ions flow into egg
• potential of egg plasma membrane changes to positive
• sets of chain reaction

Question 4

what does the acrosomal reaction work to do

Answer 4

fast block to polyspermy

Question 5

describe the cortical reaction

Answer 5

• change in membrane potential results in release of calcium
• cortical granules fuse with plasma membrane
• vitelline layer is polymerised and fertilisation membrane forms

Question 6

what is the job of the cortical reaction

Answer 6

slow block to polyspermy

Question 7

what does the change in plasma membrane potential cause

Answer 7

• metabolic changes e.g. protein synthesis

- PH changes

Question 8

3 main stages of development

Answer 8

1) cleavage (division)
2) gastrulation
3) organogenesis

Question 9

3 types of cleavage and what types of ova they occur in

Answer 9

1) complete cleavage - isolecithal
2) incomplete cleavage (just on top)- telolecthical
3) superficial (round the outside) - centrolecthical
- different amounts of yolk have varying effects on cleavage patterns

Question 10

what is inderterminate cleavage

Answer 10

radial - cleavage planes parallel or perpendicular to vertical axis

Question 11

what is determinate cleavage

Answer 11

spiral - plane of division is diagonal to vertical axis of embryo - embryo twists as it develops

Question 12

describe a morula and blastula

Answer 12

morula - solid ball of cells

blastula - hollow ball of cells

Question 13

define gastrulation

Answer 13

when a blastula forms into a gastrula - cells in vegetal pole buckle in forming blastopore and archenteron

Question 14

what does triploblastic mean

Answer 14

3 body layers

Question 15

what are the 3 primary germ layers

Answer 15

1) endoderm - gut
2) ectoderm - outer covering
3) mesoderm - muscles, blood system

Question 16

acoelomate

Answer 16

lack body cavity - solid layer of mesoderm

Question 17

pseudocoelomate

Answer 17

body cavity only partially lined by mesoderm

Question 18

coelomate

Answer 18

body cavity lined completely by mesoderm

Question 19

2 main branches of metazoans

Answer 19

1) protostomes

2) deuterostomes

Question 20

describe protostomes

Answer 20

cleavage = spiral +determinate 
coelom = formed by proliferation of cells
blastopore = mouth first anus second

Question 21

describe deuterostomes

Answer 21

cleavage = radial + interdeterminate 
coelom = formed by pocketing out of archenteron 
blastopore = anus first

Question 22

what is the difference between direct and indirect development

Answer 22

direct = no larval stage 
indirect = larval stage

Question 23

what types of eggs are likely to be produced in tough and rich environments

Answer 23

tough = lots of yolk + fewer eggs 
rich = lots of eggs and little yolk