Lecture 4: Origin of Prokaryotes and Eukaryotes

Question 1

Rocks of suitable age contain three types of fossil evidence for prokaryote life:

Answer 1

1) Fossil Stromatolites
2) Fossil microorganisms
- silicified in cherts
- resistant cell walls called acritarchs preserved in siltstones
3) Carbonaceous matter that can be identified chemically as the product of ancient life

Question 2

Fossil stromatolites:

Answer 2

cyanobacteria on surface & anaerobic bacteria in centre

1) sediment settles
2) live substances rise to surface
3) etc keeps going

Question 3

cherts

Answer 3

silica grown as nodules

Question 4

where are siltstones positioned?

Answer 4

bottom of ocean

Question 5

Prokaryotes dominated the planet for

Answer 5

some 2 billion years

Question 6

Prokaryotes remain..

Answer 6

relatively unchanged to the present day

Question 7

by 3,500 Ma we have…

Answer 7

advanced prokaryote life in the oceans. Consisted on complex and diverse communities of stromatolite forming communities on the floors of shallow seas & free living prokaryotes floating around in the oceans.
Both communities include cyanobacteria that produce oxygen as a biproduct of their metabolism.

Question 8

The oxygen as a biproduct from the cyanobacteria means the-

Answer 8

environment becomes aerobic

Question 9

Evidence for the earth becoming aerobic:

Answer 9

• banded iron formations
• pyritic conglomerates
• red beds

Question 10

BIFs

Answer 10

Banded Iron Formations

Question 11

Early Oxygen Sinks:

Answer 11

1) Volcanic gases that readily combine with O2 (N–NO & NO2; H–H2O; CH4—CO2; H2S–SO4)
2) Dissolved iron that scavenged O2 to form BIFs
3) Microorganisms carrying out aerobic respiration (O2 + organic matter = H2O + CO2 + cellular energy). The earliest organisms were no doubt facultative, respiring aerobically when O2 was available, but switching back to anaerobic fermentation when it was in short supply

Question 12

2 consideration for considering the origin of eukaryotes

Answer 12

• when were conditions suitable for the origin of eukaryotes
• fossil evidence for eukaryotes

Question 13

by 2 billion years ago some acritarchs are large enough to,,

Answer 13

suggest that they were Eukaryotes

Question 14

2 theories of how eukaryotic cell originated:

Answer 14

1) Symbiosis

2) Elaboration of cell membrane

Question 15

Symbiosis steps:

Answer 15

1) Thermoplasma-like Archaebacterium (nucleosome-like containing chromosome) is engulfed by photo-eukaryote cell = Eukaryotic cell

Question 16

Symbiosis has been used to explain the origin of eukaryote:-

Answer 16

• mitochondria
• Chloroplasts
• Flagella & Cilia
• mitosis?