lecture 2 - 01/10/24

Question 1

What is fertilisation?

Answer 1

Fusion of sperm and egg

Question 2

What is cleavage?

Answer 2

mitotic cell division after fertilisation
- no time for cells to increase in size

Question 3

What are the 2 types of cleavage?

Answer 3

spiral and radial

Question 4

Describe spiral cleavage

Answer 4

seen in protostomes animals

cell pattern rotates by 45 degrees
e.g. pond snail

Question 5

Describe radial cleavage

Answer 5

seen in deuterostomes animals
cells stack in an aligned manner
e.g. sea urchin

Question 6

Describe the blastula stage

Answer 6

• dividing cells are aligned in the outer layer
• inside of the embryos forms a cavity called
  ‘blastocoel’
• cells in blastula stage are not easily
  differentiated

Question 7

What does the blastocoel contain?

Answer 7

salt water

Question 8

What are the 3 germ layers?

Answer 8

ectoderm
mesoderm
endoderm

Question 9

What is a germ layer?

Answer 9

• a group of cells which are specified to
  become certain cell fates
• formed at the late blastula stage

Question 10

What does the ectoderm form in humans?

Answer 10

neutral plate
- forebrain
- midbrain
- hindbrain
- spinal cord

neutral crest

placodes
- eyes
- nose
- ear

epidermis (skin)

Question 11

What does the mesoderm form in humans?

Answer 11

muscle
bone
kidney
heart
blood

Question 12

What does the endoderm form in humans?

Answer 12

intestine
pharynx
liver
stomach

Question 13

Describe the trend between complexity and number of germ layers

Answer 13

As number of germ layers increases, complexity increases

Question 14

What is the term for 2 germ layers?

Answer 14

diploblastic

Question 15

What is the term for 3 germ layers?

Answer 15

triploblastic

Question 16

What does evolution of germ layers allows?

Answer 16

it allows the development of different tissues with complex functions

Question 17

How many germ layers does porifera have?

Answer 17

no germ layers

Question 18

How many germ layers does Ctenophora and Cnidaria have?

Answer 18

2
diploblastic

Question 19

How many germ layers do the Bilateria have?

Answer 19

3
triploblastic

Question 20

Describe Gastrulation

Answer 20

rearrangement of cells
- involution and internalisation of mesoderm
and endoderm cells

specification of cell fates
- ectoderm > epidermis, neuron
- mesoderm > muscle, blood etc.
- endoderm > digestive system

Question 21

What is radial symmetry?

Answer 21

one main axis

Question 22

What is bilateral symmetry?

Answer 22

Plane of symmetry runs from anterior to posterior.

Question 23

Explain the evolution of symmetrical animals

Answer 23

asymmetrical –> radially symmetrical –> bilaterally symmetrical

Question 24

What is the exception that breaks the bilaterally symmetrical rule in the bilateral?

Answer 24

echinoderms are bilateria but have lost bilateral symmetry

Question 25

Why is bilateral symmetry important?

Answer 25

It facilitated dorsal-ventral differentiation of more complex tissue development

Question 26

What groups are in protostomia?

Answer 26

ecdtysozoa lophotorochozoa

Question 27

What is the difference between cleavage pattern in protostomes and deuterostomes?

Answer 27

protostomes = spiral cleavage deuterostomes = radial cleavage

Question 28

What is the difference between cell fates during cleavage in protostomes and deuterostomes?

Answer 28

protostomes = determinate cleavage - tissue e.g. skin, muscle deuterostomes = indeterminate cleavage - complete larvae

Question 29

Protostomes vs deuterostomes mouth or anus first?

Answer 29

protostomes - blastopore forms mouth deuterostomes - blastopore forms anus

Question 30

Do acoelomates have a body cavity?

Answer 30

no body cavity space between gut and muscular wall filled with masses of cells - mesenchyme

Question 31

Do pseudocoelomates have a body cavity?

Answer 31

yes - pseudocoel muscle (mesoderm derived) present only on outer side of pseudocoel no mesoderm surrounding internal organs

Question 32

Do coelomates have a body cavity?

Answer 32

yes - coelom internal organs surrounded by muscular tissue - peritoneum coelom is enclosed both inside and out by mesoderm

Question 33

Explain the evolution and complexity of body cavity

Answer 33

acoelomate --> pseudocoelomate --> coelomate gets more complex -->

Question 34

How do earthworms move?

Answer 34

peristalsis bristles anchor the worm and muscles manipulate the fluid in the coelom flattening and lengthen sections of the animal allowing it to move

Question 35

What is a hydrostatic skeleton?

Answer 35

closed body compartment filled with fluid under pressure

Question 36

Are fluids compressible?

Answer 36

fluids are relatively uncompressible