Origin of microbial life, evolution, and modern diversity

Question 1

Describe the de Novo hypothesis of the origin of life on Earth

Answer 1

Life originated on Earth from a primordial non-oxidising atm including of H2O, H2, CO2, and N

Question 2

Describe the Panspermia hypothesis of the origin of life on Earth

Answer 2

Life arrived on Earth, preformed as spores, enveloped in mantle formed by a collision between between a life-bearing planet and comet/meteorite

Question 3

What must be true is the de Novo hypothesis is true?

Answer 3

The assembly of macromolecules into primitive wells would have included the evolution of proteins to RNA to DNA

Question 4

What would have happened to protocells in the de Novo hypothesis?

Answer 4

They would have evolved to LUCA and then to modern prokaryotic cells

Question 5

Describe LUCA

Answer 5

Anaerobic, hyperthermophilic, halophilic, and chemolithotrophic

Question 6

Where did LUCA obtain energy and carbon from?

Answer 6

Inorganic sources
Used H2 and H2S as e- donors and CO2 as e- accpetor
Fixed CO2 as carbon source

Question 7

According to the organic soup theory, what would the first prokaryotic cells have been?

Answer 7

Heterotrophs that could live without free oxygen
Fed on externally available, abiotically synthesised organic molecules

Question 8

Why did autotrophy emerge?

Answer 8

To sustain life because abiotic synthesis was rate-limiting and the demand could not be met

Question 9

Describe the two types of autotrophs that emerged to sustain life

Answer 9

Chemolithotrophs obtain energy from oxidation of inorganic compounds
Photolithotrophs obtain energy by converting sunlight into chemical energy

Question 10

According to the surface metabolist theory, what would the first cells have been?

Answer 10

Autotrophs

Question 11

What conditions allowed the evolution of the first eukaryotic organisms?

Answer 11

Protection from U.V. by the ozone layer
Increased O2 acts as e- acceptor for high energy metabolism

Question 12

What orgenelles were needed by new photosynthesising and respiring cells?

Answer 12

Chloroplasts and mitochondria (respectively)

Question 13

How were the first chloroplasts and mitochondria developed?

Answer 13

Endosymbiosis of primitive cells and cyanobacteria-like organisms

Question 14

What are Whittaker’s 5 Kingdoms based on?

Answer 14

Nutrition (photosynthesis, absorption, ingestion)
Dominated by plants, fungi, and animals

Question 15

What are Woese’s 3 Domains based on?

Answer 15

Evolutionary relationships inferred by sequence comparision (rRNA genes)
Dominated by microorganisms

Question 16

Why is there bias in our understanding of microbial diversity?

Answer 16

It is largely based on cultured organisms

Question 17

What is the result of prokaryotes being less limited than eukaryotes by conditions?

Answer 17

They have a higher proportion of carbon biomass

Question 18

What is the most physiologically diverse bacterial group? What are the five types?

Answer 18

Proteobacteria
α, β, γ, δ, ε

Question 19

Briefly describe alphaproteobacteria

Answer 19

Agricultural importance
Includes nitrate oxidisers, and N-fixers
Includes purple non-sulphur bacteria (anoxygenic photosynthesis)

Question 20

Briefly describe betaproteobacteria

Answer 20

Biotechnological importance
Includes soil contaminant degraders

Question 21

Briefly describe deltaproteobacteria

Answer 21

Includes sulphate-reducers and Fe(III), Mn(IV), and S-reducers

Question 22

Briefly describe gammaproteobacteria

Answer 22

Includes anoxygenic photosynthetic purple sulphur bacteria

Question 23

Briefly describe epsilonproteobacteria

Answer 23

Includes chemolithotrophic sulphur bacteria
Includes types of digestive system pathogens

Question 24

Describe green sulphur bacteria

Answer 24

Anoxygenic photosynthetic bacteria that use sulphide (not water) as e- donor for reducing CO2 fixation

Question 25

What is the CFB group of bacteria?

Answer 25

Cytophaga/Flavobacterium/Bacteriodes

Question 26

Describe Cytophaga and relatives

Answer 26

Fish pathogen that can degrade macromolecules

Question 27

Describe Flavobacteria and relatives

Answer 27

Common in most aerobic environments
Gram -tive
Yellow pigmented

Question 28

Describe Bacteriodes and relatives

Answer 28

Anaerobic
Gram -tive
Some are pathogenic, commonly found in mammalian intestinal tract

Question 29

Give five examples of groups of bacteria

Answer 29

CFB, Fibrobacter, Cyanobacteria, Chlamydia, Green sulphur bacteria

Question 30

Give two groups of Euryarchaeota

Answer 30

Methanogens and extreme halophiles

Question 31

Give four other phyla of Archaea

Answer 31

Thermoplasma, Thermococcales, Archaeoglobus, Crenarchaeota

Question 32

What are the three main groups of Eukarya?

Answer 32

Animals, fungi, plants

Question 33

Describe Protozoa

Answer 33

Single-cell eukaryotes with no chlorophyll, that graze on bacteria
Form symbiosis with algae and can be pathogenic

Question 34

Describe viruses

Answer 34

DNA or RNA surrounded by protein case
Infects all cellular life forms