1: Origin of prokaryotes & eukaryotes

Question 1

What are the 3 types of fossil evidence for prokaryote life?

Answer 1

1) fossil stromatolites
2) fossil microorganisms
3) Carbonaceous matter

Question 2

Describe 2 ways in which microorganisms can be fossilised

Answer 2

Silicified in cherts (rare, 3D preservation on bacteria)
Resistant cell walls (acritarchs preserved in siltstones)

Question 3

What are BIFs?

Answer 3

Banded Iron Formations

Question 4

Describe early oxygen sinks

Answer 4

• Volcanic gases (early atmosphere) readily react with O2 (released by photosynthesising bacteria)
  N→NO & NO2, H→H2O, CH4→CO2,
• Dissolved iron that scavenged O2 to form BIFs
• Early microorganisms were facultative

Question 5

Early microorganisms were faculative, what does this mean?

Answer 5

respiring aerobically when O2 available but switching to anaerobic when in short supply

Question 6

Where does evidence for early O2 sinks come from?
+ explain how they evidence this

Answer 6

BIFs → suggests iron in oceans has been used up by O2

Red beds → can only form if O2 in atmosphere
At some point 2bya the atmosphere became aerobic

Pyritic conglomerates → iron pyrate (fools gold)

Question 7

Describe the great oxygenation event

Answer 7

• Occurred somewhere between 2.4-1.8 Ma
• Huronian Ice age around this time, caused by the elimination of atmospheric methane during the GOE
• Anaerobic organisms forced into small areas that remain anaerobic e.g deep sea floor

Question 8

Fossil evidence for eukaryotes

Answer 8

By 2 billion years (atmosphere just turning aerobic) some acritarchs were large enough to suggest they were eukaryotes

Question 9

What are the 3 theories for the origin of eukaryotes?

Answer 9

1) Symbiosis (Cell engulfs smaller microorganism)
2) Elaboration of cell membrane
3) Multiple symbiotic events

Question 10

Describe the symbiosis theory in relation to mitochondria

Answer 10

Have own DNA
Independently replicate during mitosis
Semi-autonomous
Independent purple bacteria that could respire aerobically that were engulfed by anaerobic bacteria
Mitochondria all related - probably engulfed just once

Question 11

Describe the theorised origin of chloroplasts

Answer 11

Cyanobacteria
Similar to mitochondria
Engulfed by bacteria to allow them to photosynthesis