Eukaryotes and Cambrian explosion W5L1

Question 1

Eukaryotes origin

Answer 1

endosymbiotic origin

evident in genetics of different cell parts

Question 2

Eukaryotes sexual reproduction

Answer 2

greater genetic variability > evolution

greater diversity and disparity •

Question 3

Eukaryotes size

Answer 3

larger size thank bacteria cells
resources
metabolism
this can easiyl place fossil cells bcs little chance that internal structures will prevail so other diagnostic features

Question 4

Endosymbiotic events

Answer 4

ndosymbiotic events (bacterial cell eats other cell) → organelles in  cells
various engulfing events → eventually genetically coded → complex cells with remnants of engulfed prey inside them

Question 5

bacterial cells reproduce

Answer 5

bacterial cells (prokaryotes) reproduce asexually (cloning/ splitting)

Question 6

eukaryotes reproduce

Answer 6

eukaryotes can also produce asexually (single cell algae) but also add sexual reproduction
recombining genetic material
mixing DNA “speeding up evolution”

Question 7

Snowball earth

Answer 7

single cells can live under ice but most organisms struggle

little pulse of banded iron formations, relatede to end of one snowball earth

Question 8

Precambrian provides

Answer 8

the Precambrian geological record provides context for the timing, environmental conditions
and types of early life
• the record reveals a very long period (~3.5 b.y.) characterised by small, microbial organisms,
prior to the rapid emergence of large metazoans
• nevertheless, this interval saw the emergence of life, anoxygenic phyotosynthesis, then oxygenic
photosynthesis, oxygenation of the planetary surface, aerobic respiration and eukaryotic cells

Question 9

Ediacaran Fauna

Answer 9

Ediacaran fossils 540-580 Ma
• large, relatively complex and diverse structures (radial, bilateral)
• unmineralized, i.e., soft bodied
• appeared after the final snowball episode (Gaskiers)
diverse group of animals
Ediacaran animals as precursors for “ real animal” still big gap betwee new ones

Question 10

Animals definition

Answer 10

Animals are multicellular eukaryotic organisms that usually consume organic material, breathe oxygen, are able to move, can reproduce sexually

Question 11

Animal body definition

Answer 11

everal distinct body plans defined by number of enveloping walls of tissue and presence or absence of coelom (body cavity)

Question 12

parazoan

Answer 12

groups of cells in 2 layers not differentiated into tissue types

Question 13

Diploblastic

Answer 13

2 layers separated by the acellular, gelatinous mesogloea

Question 14

Triploblastic

Answer 14

3 layers of tissues from the outside in: the ectoderm, mesoderm and endoderm. Also bilateral symmetry

Question 15

Animal cells

Answer 15

Animals are unique in having the ball of cells of the early embryo develop into a hollow ball or blastula
Around 12 major animal groups or phyla, 35 in total

Question 16

EEdiacaran fossils

Answer 16

Ediacarans preserved as moulds/casts/impression
often in sands, shallow-water environments
no mineralised skeletons
some multicellular fossils

Question 17

Ediacaran fossils perserved

Answer 17

no predation or scavenging
 pervasive microbial mats
 low oxygen?
different ocean chemistry
 pyrite ‘crusts’
silica cementation?
usually get eaten scavenged immediately, will be deconstructed (bacteria etc) 
so kinda strange that the fossils are still present 
must have been unusual environment

Question 18

Ediacaran animals meaning

Answer 18

why did they go extinct?
are they the precurosur, well gap in evolutional
are the Ediacaran fossils remains of animals?
what happened to the Ediacarans?
extinction?, gave rise to other animals?
when did true animals appear?

Question 19

How reliable ediacaran fossil record?

Answer 19

embryo fossil evidence
molecular clock evidence
stromatolite decline
trace fossils
• is the Cambrian explosion ‘real’
why the acceleration of animal evolution?
environmental trigger?
genetic trigger?
• why rapid ‘disparity’ followed by 530 my of stablility?
problems
correlation and dating of unfossiliferous rocks
preservation: old rocks, soft-bodied and or small animals?

Question 20

Molecular clock evidence

Answer 20

biomarker to date where fossils were found
but markers often dont match - they more suggest that fossil record didnt cpature it as “explosion”
given the discrepancies there is still a period where a lot happened

Question 21

why cambrian expolsion

Answer 21

Oxygen
 when did the rise occur?
threshold
 respiration
ozone
• predation - ‘arms race’
evolution of eumetazoans
move into planktonic niche
food that allows to move out into new habitats
eyes for the first time
first time using sight senses, for hunting
• climate - oceans
post-Snowball Earth
 genetic ‘leap’
trigger genes, e.g., Hox genes, allow spinal shape
neural tissue

Question 22

Tommotian

Answer 22

Lower cambrain, small shelly fauna

sponges and mullosc

Question 23

Burgess SHale

Answer 23

really changed how Cambrian was percieved, unique window cambrain life
submarine landside deposit
• high diversity (120 spp.)
• ~98% soft bodied
more mature ecosystem
Simple ecosystem
40% trilobites, 25% worms
Preservation as carbon films
soft bodied animals

Question 24

Anthropod as

Answer 24

rthropod as first Apex predator maybe
“normal” animals many many arthropods
primitive arthropods such as Opabinia

Question 25

fossil record of precambrian tells us

Answer 25

evolution of eumetazoan grade and predation ecological strategy led to
acceleration of evolution
• last common ancestor of eumetazoans was a sponge
• trigger may have been lack of food following a snowball glaciation forcing a
switch in trophic strategy
• move into the pelagic realm may have driven second Ordovician radiation
• rapidity of disparity due to expansion of regulatory genes acting on
relatively conservative animal genome