Development

Question 1

Sexual reproduction

Answer 1

● Haploid sperm meets haploid egg
↳diploid Zygote
● Diploid stage dominates life cycle
Zygote undergoes Cleavage (Cleavage causes cell division without cell growth, i.e. not changing the overall size of the embryo, like splitting a party balloon into sections)
↳Blastula (hollow ball) The hollow ball forms an invagination (like a pouch)
that sets up the tissue layers that will ultimately
form the adult body parts.
● Blastula undergoes Gastrulation
↳Gastrula

Question 2

Exceptions to sexual
reproduction

Answer 2

● Fragmentation (e.g.
planarians, sea stars)
● Parthenogenesis (e.g. aphid giving birth to live young via unfertilised egg)

Question 3

Ectoderm, Endoderm, Mesoderm

Answer 3

● Ectoderm – surface of embryo, outer animal layer
● Endoderm – lines developing digestive tract
● Mesoderm – between Ectoderm and Endoderm

Question 4

Diploblastic and Triploblastic

Answer 4

Diploblastic
2 germ layers e.g. jelly fish

Triploblastic
3 germ layers e.g. all bilateral Animals

Question 5

Body cavity (coelom - hollow cavity)

Answer 5

Fluid/air filled space between digestive tract and outer wall
Function -
Cushioning of organs, Allows organs to grow and
move, Act as hydrostatic skeleton

Question 6

Acoelomates,Pseudocoelomates, Coelomates - body cavity

Answer 6

• Acoelomates – no body cavity at all e.g. flatworms
• Pseudocoelomates – formed when mesoderm only partially enters the blastocoel, e.g. nematodes
• Coelomates – formed from tissue derived
  from mesoderm e.g. earthworm

Question 7

Axes of symmetry

Answer 7

● None (sponges)
● Radial – no left or right, no front or back
● Bilateral – 2 axis of orientation front to back & left and right

Question 8

Animal Body Plans

Answer 8

A body plan is “an assemblage of morphological and developmental features shared among a group of animals” typically featuring:
● Symmetry
● Embryonic tissue layers
● Body cavities (also segmentation, appendage disposition…)

Question 9

Cambrian explosion

Answer 9

Most animal body plans were established during the cambrian explosion
Cambrian explosion c. 539 Ma - a period of just 13-25 million years when
almost all complex animal life appears in the fossil record

Question 10

Avalon explosion

Answer 10

Avalon explosion c. 575 Ma – a pre-cambrian event that might have established more
complex animals than previously thought

Question 11

Main differences between Protostome Annelids,
Hexapods, Crustaceans &
Molluscs
Deuterostome Echinoderms
& Chordates

Answer 11

● Cleavage type
● Coelom formation
● Fate of the Blastopore

Question 12

Protostomes - cleavage

Answer 12

In protostomes, when cleaving from 4-cells to 8-cells, the cells twist. This carries on in further cell divisions to create a spiral-shaped embryo
They also have determinate cleavage, meaning each cell’s fate to become different tissue types is pre-determined

Question 13

Deutrostomes - cleavage

Answer 13

In deuterostomes they have radial cleavage, so do not spiral. Each cell’s fate is also indeterminate, meaning any cell has the capacity to become any other future
tissue type. This means that identical twins are possible in deuterostomes

Question 14

Protostomes - coelom

Answer 14

In protostomes the coelom is formed inside the
mesoderm from the outset, as a pouch from the archenteron

Question 15

Deuterostomes - coelom

Answer 15

In deuterostomes the coelom forms through folds in the archenteron

Question 16

Blastophore

Answer 16

The blastopore is that first invagination that forms in the blastula when it goes through gastrulation
It’s the fate of this hole that gives rise to the names of these two groups, either forming the mouth or anus

Question 17

Homeotic Transformations

Answer 17

When one body part grows in the wrong place this is called a homeotic transformation, these have been a focus of research because you can easily look for mutants in wild or artificially mutated populations

Question 18

Hox genes

Answer 18

Regulatory genes that
tell the developing embryo where to form different limbs/organs (but not
how to form them)
Hox genes (and other regulatory genes) all contain the same short of
DNA sequences called Homeoboxes

Question 19

What are the genes controlling developmental pathways and networks

Answer 19

They are highly
conserved in bilateria
Pax 6*
Hox*
Brachyury
Distalless*
BMP4/Chordin

Question 20

Direct Development

Answer 20

The juvenile form largely
resembles the adult form

Question 21

Indirect development

Answer 21

The animal’s
juvenile stages are morphologically
distinct from the adult, with sometimes multiple transient stages of maturation e.g. typical insect life cycle involves:
egg→ larva→ pupa→ adult

Question 22

The animal kingdom is a
monophyletic clade called …

Answer 22

Metazoa

Question 23

Most phyla belong to …

Answer 23

Bilateria

Question 24

Ecdysozoa

Answer 24

includes
arthropods, nematodes +
other phyla, they typically:
● Excrete exoskeleton
● Undergo moult

Question 25

Lophorophozoa

Answer 25

Includes annelids, molluscs and many other phyla.
They either:
● Develop a lophophore (crown ciliated tentacles involved in feeding (e.g. Brachiopods & ectoprocts), OR
● Have a distinctive development stage called Trochophore larva (e.g. molluscs & annelids)