Lecture Two

Question 1

What organisms followed the anaerobic autotrophs and when did this occur?

Answer 1

Photoautotrophs with oxygenic photosynthesis. Developed around 3.5 billion years ago.

Question 2

What was the key innovation of photoautotrophs that gave them an advantage over the anaerobes?

Answer 2

Their use of water as the electron donor (water is split). The advantage came about because water was very plentiful. Oxygen is a by-product of this (hence the term oxygenic photosynthesis).

Question 3

What were the first fossil organisms?

Answer 3

Cyanobacteria, occurred in stromatolites 3.5 BYA.

Question 4

How are stromatolites formed?

Answer 4

The photosynthetic bacteria grows in mounds that are eventually covered by debris (primarily Calcium carbonate which precipitates out of the water). As the bacteria get covered they die, while new bacteria grows on top of the debris. This occurs again and again, producing a fossilized layered rock that is able to preserve.

Question 5

What Canadian reserves have plenty of stromatolites?

Answer 5

Red Lake, Ontario.
Steep Rock Lake, Ontario.
Yellowknife, NWT.

Question 6

Where do modern stromatolites grow?

Answer 6

Shark Bay, Western Australia. There is approximately 3 billion cyanobacteria/m2.

Question 7

Where are modern stromatolites found?

Answer 7

Generally in hot or hyper-saline environments where they are free from grazing and burrowing animals (generally reach 1.5 metres high, while ancient ones can get up to 10 m)

Question 8

Where Cyanobacteria the first life forms?

Answer 8

Unlikely, however they are likely the first life form that had hard parts that could fossilize.

Question 9

How did oxygen appear in the atmosphere?

Answer 9

Ferrous iron suspended in solution was very plentiful in ancient anoxic oceans. Once oxygenic photosynthesis started with the advent of Cyanobacteria, oxygen accumulated in the atmosphere and the surface waters of the ancient seas. This resulted in the oxidation of ferrous iron to ferric iron in these surface waters.
Ferric iron, with oxygen attached, precipitated to the sediments - leaving banded iron formations. By 2 BYA the ferrous iron within the oceans had largely been precipitated to the ocean floor.

Question 10

What is the iron content of the oceans like today?

Answer 10

Currently very low in solution because most of it has been locked up in sediments following oxidation.

Question 11

Is there more oxygen in the atmosphere (currently) or in banded iron formations?

Answer 11

There is currently 20x more oxygen in BIFs than in the atmosphere as a result of billions of years of oxygen production by photosynthesis.

Question 12

What did early biodiversity on earth consist of from 3.5 BYA to 2.2 BYA?

Answer 12

Only of prokaryotes.

Question 13

How long have Cyanobacteria occupied the earth?

Answer 13

For at least 3.5 BY and had been the dominant life form for more than 1.5 BY.

Question 14

What three effects did the build up of oxygen in the atmosphere have?

Answer 14

1. A rapid expansion in the biodiversity of aerobic microorganisms (with a concurrent reduction in anaerobic prokaryotes).
2. The first ice age (snowball Earth)
3. Providing the atmosphere needed for the next major evolutionary step (origin of eukaryotes)

Question 15

What major extinction even is not included in the major five and occured 2.2 BYA?

Answer 15

The Great Oxygenation Event

Question 16

What is The Great Oxygenation Event?

Answer 16

When the iron on Earth had absorbed as much oxygen as it could hold, the remainder remained in the atmosphere. Free oxygen was toxic to anaerobic organisms, and wiped out most of the Earth’s anaerobic inhabitants. Eventually aerobic organisms (including Eukaryotes) evolved to take advantage of the new oxygen.

Question 17

What was the Huronian glaciation and what triggered it?

Answer 17

The Huronian glaciation was triggered by free oxygen reacting with atmospheric methane, greatly reducing its concentration. The Huronian glaciation was the longest snowball Earth episode in Earth’s history.

Question 18

True or False: Archaea and bacteria developed from a common ancestor?

Answer 18

True.

Question 19

What do Archaea have genes similar to?

Answer 19

Archaea have genes similar to both bacteria and eukaryotes because eukaryotes branched off from archaeans millions of years later.

Question 20

Are archaeans more closely related to eukaryotes or bacteria?

Answer 20

Eukaryotes.

Question 21

What is the evolution of eukaryotic life based on?

Answer 21

Endosymbiosis; one species (the endosymbiont) living within another species (the host). This development of organelles is known to be from the plasma membrane itself. The addition of the energy source of the cell (mitochondria and chloroplasts) are thought to have occurred via failed phagocytosis. Heterotrophic cell, already possessing some organelles, acquired chloroplasts by incorporating Cyanobacteria as the endosymbiont (mitochondria were derived by other symbionts).
Normally the engulfed cell would be digested, instead a mutualistic symbiotic relationship evolved. The host cell provided inorganic nutrients (Nitrogen and Phosphorus) and shelter (membrane); cyanobacterium and mitochondria provided energy. As the symbiosis grew and the hose became more interdependent, the two become a single organisms, or an obligate mutualistic relationship.

Question 22

What is the fact the Eukaryotic chloroplast has cyanobacterial properties evidence for?

Answer 22

Evidence for the theory of endosymbiosis.

Question 23

What cyanobacterial properties does the Eukaryotic chloroplast have?

Answer 23

Remnant DNA in chloroplast are similar to cyanobacterial DNA in that its circular and lacking histones (proteins found in eukaryotic cell nuclei that package and order the DNA into nucleosomes).
Ribosomes in chloroplast are similar to cyanobacterial ribosomes (small).
Nucleotide sequences of DNA and ribosomal RNA are similar.

Question 24

What is the fact that actual cyanobacteria occur within the cells of many organisms evidence for?

Answer 24

Evidence for the theory of endosymbiosis

Question 25

What are examples of cyanobacteria occurring within the cells of organisms?

Answer 25

1. Diatoms (for nitrogen fixation)
2. Fungi (nitrogen fixation)
3. Lichens
4. Cycads (land plants).

Question 26

What is the Theory of Secondary Endosymbiosis?

Answer 26

A eukaryote engulfing another eukaryote’ explains how other algae obtained chloroplasts (e.g. Protista and Chromista). These ideas are more complex and often unresolved.

Question 27

What evidence supports the Theory of Secondary Endosymbiosis?

Answer 27

Occurrence of more than two envelopes around the chloroplast of some algae.
Small nuclei and eukaryotic-sized ribosomes are found outside the two inner chloroplast envelopes, but inside the chloroplast itself, thus it must have initially been a eukaryote.

Question 28

What is the rise of eukaryotic multicellular organisms directly linked to?

Answer 28

The rise in oxygen levels due to the effect of size on the surface volume to ration and oxygen’s ability to diffuse into aerobic cells. Large cells have a significantly harder time diffusing oxygen into their centre than smaller cells, thus larger cells need a higher level of oxygen to develop and thrive.

Question 29

When do Eukaryotic cells first appear?

Answer 29

Between 2-2.5 BYA.

Question 30

When do multicellular eukaryotes first appear?

Answer 30

1.5 BYA.

Question 31

When are three of the six kingdoms present by?

Answer 31

1.5 BYA.

Question 32

What are the two theories for multicellular evolution?

Answer 32

1. Cells found each other and aggregated to form colonies.

2. Cells remained attached after cell division years ago.

Question 33

What are some advantages to being multicellular?

Answer 33

Increased protection from the environment (less surface area exposed to the environment); get larger and become a better predator; division of labour, specialization of cells in organism, more efficient.

Question 34

What are some disadvantages to being multicellular?

Answer 34

The larger you get the more you must specialize because most of your cells are not able to communicate directly with the environment.