C17 Sample Questions from Brock

Question 1

The microorganisms that are thought to resemble the first cellular forms of life on Earth are
A) H2-oxidizing hyperthermophiles.
B) acidophilic
C) the Nanoarchaeota.
D) fermentative thermophiles.

Answer 1

A) H2-oxidizing hyperthermophiles.

Chapter 17 discusses how the earliest forms of life likely thrived in hot, anaerobic environments, much like the conditions where H2-oxidizing hyperthermophiles are found today. These organisms utilize H2 as an energy source, a metabolism thought to be ancient.

Question 2

Which statement is TRUE of methanogenic and extremely halophilic Archaea?
A) The methanogens are obligate aerobes; the extreme halophiles are obligate anaerobes.
B) The methanogens are obligate anaerobes; the extreme halophiles are mostly obligate aerobes.
C) Both the methanogens and the extreme halophiles are obligate aerobes.
D) Both the methanogens and the extreme halophiles are obligate anaerobes.

Answer 2

B) The methanogens are obligate anaerobes; the extreme halophiles are mostly obligate aerobes.

Methanogens are strict anaerobes, poisoned by oxygen. While some extreme halophiles can grow anaerobically, most require oxygen for respiration.

Question 3

Archaea are
A) primarily ancient organisms that have not evolved very much in the last billion years.
B) phylogenetically diverse, but functionally restricted to extremophiles and chemolithotrophs.
C) a group of diverse microorganisms that inhabit almost every environment on Earth, including the colon of humans and other mammals.
D) functionally diverse, but restricted to thermophilic or hyperthermophilic environments.

Answer 3

C) a group of diverse microorganisms that inhabit almost every environment on Earth, including the colon of humans and other mammals.

Archaea are remarkably diverse, occupying a wide range of habitats, from extreme environments to more common ones like the human gut. They are not limited to extremophiles.

Question 4

Which of the following types of metabolisms is NOT found in Archaea?
A) photosynthesis
B) chemolithotrophy
C) chemoorganotrophy
D) aerobic respiration

Answer 4

A) photosynthesis.

While some archaea use light for energy (e.g., bacteriorhodopsin in haloarchaea), they do not perform photosynthesis using chlorophyll-based systems like bacteria and eukaryotes.

Question 5

Some of the largest naturally occurring plasmids occur in the
A) methanogens.
B) Archaea lacking cell walls.
C) extreme halophiles.
D) genus Thermococcus.

Answer 5

A) methanogens.

Methanogens are indeed known to harbor some of the largest naturally occurring plasmids, particularly those belonging to the genus Methanosarcina. These plasmids often carry genes involved in various metabolic processes, including those related to methane production.

Question 6

Most haloarchaea use which of the following for electron donors?
A) amino and organic acids
B) carbohydrates
C) lipids
D) nucleic acids

Answer 6

A) amino and organic acids.

Haloarchaea primarily utilize amino acids and organic acids as electron donors for their energy metabolism in their high-salt environments.

Question 7

Some strains of haloarchaea exhibit
A) anoxic growth at the expense of sugar fermentation.
B) anaerobic respiration.
C) anoxygenic photosynthesis.
D) light-driven ATP synthesis under oxygen-limiting conditions.

Answer 7

D) light-driven ATP synthesis under oxygen-limiting conditions.

Haloarchaea can use bacteriorhodopsin to generate ATP from light, especially when oxygen is scarce.

Question 8

The cytoplasmic proteins of Halobacterium are
A) highly acidic.
B) highly basic.
C) generally neutral.
D) variable, depending on the species.

Answer 8

B) highly basic.

To maintain function in high salt concentrations, halophilic archaeal proteins have adaptations like a high proportion of acidic amino acids on their surfaces and highly basic cores. This helps prevent denaturation and precipitation in their salty cytoplasm.

Question 9

Retinal in prokaryotes is part of
A) photosynthesis.
B) phototaxis.
C) light-driven ATP synthesis.
D) light-driven ATP synthesis and phototaxis.

Answer 9

D) light-driven ATP synthesis and phototaxis.

Retinal, bound to bacteriorhodopsin, is involved in light-driven ATP synthesis. It’s also crucial for phototaxis, directing the movement of the archaea towards optimal light conditions.

Question 10

Methanogens
A) produce methane as a part of their energy metabolism.
B) utilize methane as an energy source.
C) process and store methane to detoxify it.
D) produce, utilize, and detoxify methane.

Answer 10

A) produce methane as a part of their energy metabolism.

The defining characteristic of methanogens is their ability to produce methane (CH4) as a byproduct of their anaerobic metabolism.

Question 11

What best describes the methanogens?
A) They are a monophyletic group.
B) They are phylogenetically similar.
C) They are a diverse group that is spread across at least 7 orders.
D) They are functionally but not phylogenetically diverse group.

Answer 11

C) They are a diverse group that is spread across at least 7 orders.

Methanogens are phylogenetically diverse, distributed across multiple orders within the Methanobacteriota.

Question 12

Most known methanogens are nonhalophilic
A) psychrophiles.
B) mesophiles.
C) thermophiles.
D) extremophiles.

Answer 12

B) mesophiles.

While some methanogens are extremophiles (thermophiles or psychrophiles), the majority are mesophiles, preferring moderate temperatures.

Question 13

Which of the following are NOT substrates for methanogens?
A) acetate and pyruvate
B) carbon dioxide, carbon monoxide, and formate
C) glucose and sucrose
D) methanol and methylamine

Answer 13

C) glucose and sucrose.

Methanogens utilize a limited range of substrates, primarily one-carbon compounds or acetate. They cannot metabolize complex sugars like glucose and sucrose.

Question 14

In most salt lakes, which microbial group is the major oxygenic phototroph?
A) cyanobacteria
B) Dunaliella, a eukaryotic alga
C) halophilic Archaea
D) purple nonsulfur bacteria

Answer 14

B) Dunaliella, a eukaryotic alga.

Dunaliella is a halotolerant green alga often found as the dominant phototroph in salt lakes, outcompeting most other photosynthetic organisms in these hypersaline conditions.

Question 15

What special adaptation(s) has/have Thermoplasma evolved to survive in hot acidic environments?
A) Thermoplasma stabilize their cytoplasmic membrane by incorporation of tetraether lipoglycans in the cytoplasmic membrane.
B) Thermoplasma have a reinforced cell wall containing basic amino linkers in the peptidoglycan.
C) Thermoplasma excrete hydrogen ions and import hydroxyl ions.
D) Thermoplasma are highly motile to avoid destruction.

Answer 15

A) Thermoplasma stabilize their cytoplasmic membrane by incorporation of tetraether lipoglycans in the cytoplasmic membrane.

The tetraether lipoglycans form a rigid monolayer membrane, providing stability in the harsh hot and acidic environment.

Question 16

What characteristic do bacterial mycoplasmas and the archaeal Thermoplasma and Ferroplasma have in common?
A) contain plasmids
B) hyperthermophilic
C) lack cell walls
D) relatively large genomes from duplicated genes

Answer 16

C) lack cell walls.

Both bacterial mycoplasmas and the archaeal Thermoplasma and Ferroplasma species lack cell walls. This unique characteristic makes them distinct from most other bacteria and archaea, which typically possess cell walls.

Question 17

Which genus within Archaea is capable of growth at the hottest temperature recorded of 122°C?
A) Methanopyrus
B) Thermoproteus
C) Thermosphaera
D) Pyrococcus

Answer 17

A) Methanopyrus.

Methanopyrus kandleri holds the record for the highest growth temperature of any organism, thriving at a scorching 122°C.

Question 18

Which archaeal phylum contains many extreme halophiles, methanogens, some marine hyperthermophiles, and Thermoplasma?
A) Thermoproteota
B) Methanobacteriota
C) Nanoarchaeota
D) Nitrososphaerota

Answer 18

B) Methanobacteriota.

The Methanobacteriota is a diverse phylum encompassing methanogens, many halophiles, some hyperthermophiles, and Thermoplasma.

Question 19

What makes the metabolism of Ferroglobus interesting in the context of evolution?
A) Ferroglobus is an anaerobic iron-oxidizing chemolithotrophic autotroph that may represent a key metabolism that allowed for the oxidation of ferrous iron without molecular oxygen.
B) Ferroglobus can use H2 or H2S as electron acceptors in its energy metabolism and is thermophilic, thus representing the earliest hypothesized forms of life.
C) Ferroglobus lacks cell walls and becomes encrusted in oxidized iron, suggesting that it may be an ancestor of other archaeans that lack cell walls.
D) Ferroglobus is both an iron- and nitrate-reducer and is probably the last common ancestor of all iron- and nitrate-reducing organisms.

Answer 19

A) Ferroglobus is an anaerobic iron-oxidizing chemolithotrophic autotroph that may represent a key metabolism that allowed for the oxidation of ferrous iron without molecular oxygen.

Ferroglobus’s metabolism is significant because it demonstrates how iron oxidation could occur in anaerobic conditions on early Earth, before the accumulation of oxygen.

Question 20

Which of the following bioenergetic processes CANNOT occur in hyperthermophiles?
A) chemoorganotrophy
B) chemolithotrophy
C) photosynthesis
D) chemoorganotrophy and chemolithotrophy

Answer 20

C) photosynthesis.

While some Archaea can use light for ATP production, they do not perform oxygenic or anoxygenic photosynthesis. Hyperthermophiles utilize chemolithotrophic or chemoorganotrophic metabolisms.

Question 21

Which of the following is TRUE about the crenarchael genera Sulfolobus?
A) Sulfolobus grows in sulfur-rich hot alkaline springs.
B) Sulfolobus is an anaerobic chemolithotroph.
C) Sulfolobus can grow chemoorganotrophically.
D) Sulfolobus is a gram-positive rod.

Answer 21

C) Sulfolobus can grow chemoorganotrophically.

While Sulfolobus is primarily known for its aerobic chemolithotrophic metabolism using sulfur, it can also grow chemoorganotrophically on organic carbon sources.

Question 22

____ is a strict anaerobe with irregularly disc-shaped cells and an optimum growth temperature of 105°C. It grows chemolithotrophically on H2 with S0 as an electron acceptor or chemoorganotrophically on complex mixtures of organic compounds.
A) Pyrodictium
B) Pyrolobus
C) Pyrobaculum
D) Desulfurococcus

Answer 22

A) Pyrodictium.

Pyrodictium fits the description of a strict anaerobe, irregularly disc-shaped, hyperthermophilic, and capable of both chemolithotrophic and chemoorganotrophic growth.

Question 23

Many archaeal hyperthermophiles are ________: however, Staphylothermus is a chemoorganotroph.
A) chemolithotrophs
B) mixotrophs
C) parasites
D) photoheterotrophs

Answer 23

A) chemolithotrophs.

Many hyperthermophilic archaea obtain energy from inorganic compounds (chemolithotrophy), but Staphylothermus is an exception, relying on organic matter.

Question 24

The factor that most affects the thermostability of a protein is its
A) highly hydrophobic core regions.
B) folding pattern.
C) ionic surface interactions.
D) number of hydrogen bonds.

Answer 24

B) folding pattern.

The specific 3D structure (folding pattern) of a protein is crucial for its thermostability, determining its resistance to denaturation at high temperatures.

Question 25

One factor that seems to aid in maintaining lipid stability in hyperthermophilic Archaea is that dibiphytanyl tetraether lipids form a(n)
A) covalently bonded monolayer cytoplasmic membrane.
B) interlocking bilayer cytoplasmic membrane.
C) interlocking lattice with the cell wall.
D) pseudomembrane immediately inside the cytoplasmic membrane.

Answer 25

A) covalently bonded monolayer cytoplasmic membrane.

The dibiphytanyl tetraether lipids in some Archaea form a monolayer membrane, which is more stable at high temperatures than the typical bilayer structure.

Question 26

One unusual feature of Pyrococcus is that
A) it incorporates carbon dioxide via the acetyl-CoA pathway.
B) it is very motile due to a tuft of polar archaealla.
C) it incorporates carbon dioxide via the reverse citric acid cycle.
D) it is a thermophilic aerobic chemoorganotroph that uses elemental sulfur.

Answer 26

C) it incorporates carbon dioxide via the reverse citric acid cycle.

Pyrococcus uses the reverse citric acid cycle (also known as the reductive TCA cycle) for carbon fixation, a pathway found in some other anaerobic autotrophs.

Question 27

What is the minimum concentration of sodium chloride that an extreme halophile requires for growth?
A) 1.5 M
B) 4 M
C) 6 M
D) 10 M

Answer 27

A) 1.5 M.

Extreme halophiles require high salt concentrations, with a minimum usually around 1.5 M NaCl for growth.

Question 28

Cellular integrity and cell wall stabilization of the Halobacterium are aided by
A) potassium ions.
B) chloride ions.
C) magnesium ions.
D) sodium ions.

Answer 28

D) sodium ions.

Sodium ions play a crucial role in stabilizing the cell wall and cytoplasmic membrane of Halobacterium.

Question 29

Halobacterium salinarum and certain other extreme halophiles carry out light-driven synthesis of ATP under what condition?
A) low oxygen concentrations
B) low light
C) high oxygen concentrations
D) high carbon dioxide concentrations

Answer 29

A) low oxygen concentrations.

When oxygen is limited, Halobacterium salinarum uses bacteriorhodopsin to generate ATP from light.

Question 30

Laboratory isolation of Nanoarchaeum equitans requires the presence of
A) fatty acids.
B) oxygen.
C) Ignicoccus.
D) sunlight.

Answer 30

C) Ignicoccus.

Nanoarchaeum equitans is an obligate symbiont (or parasite) of the crenarchaeon Ignicoccus, and cannot be cultivated in its absence.

Question 31

Thermostable proteins tend to have additional features that improve thermostability. Which of the following is NOT one of these features?
A) increased ionic interactions on the protein surfaces
B) highly hydrophilic cores
C) decreased tendency of the protein to unfold
D) highly hydrophobic cores

Answer 31

B) highly hydrophilic cores.

Thermostable proteins typically have highly hydrophobic cores, which contribute to their stability at high temperatures.

Question 32

Extremely halophilic Archaea often form ________, probably in order to access _______.
A) stalks / nutrients
B) intracellular inclusions / elemental sulfur
C) gas vesicles / oxygen
D) intracellular membranes / sunlight

Answer 32

C) gas vesicles / oxygen.

Some halophilic Archaea form gas vesicles to maintain buoyancy in the water column, allowing them to access oxygen and light for energy generation.

Question 33

Compatible solutes counteract the tendency of a cell to become
A) buoyant in high ionic strength environments.
B) hyperosmotic in low ionic strength environments.
C) dehydrated in high ionic strength environments.
D) viscous in low ionic strength environments.

Answer 33

C) dehydrated in high ionic strength environments.

Compatible solutes help maintain cell turgor pressure and prevent dehydration in high-salt environments by balancing the osmotic pressure.

Question 34

The ribosomes of Halobacterium require high levels of _____ for stability and activity.
A) KCl
B) NaCl
C) NaSO4
D) acidic amino acid

Answer 34

A) KCl.

High potassium chloride concentrations are necessary for the stability and function of Halobacterium ribosomes.

Question 35

The cytoplasmic membrane of Thermoplasma contains a lipopolysaccharide-like material called lipoglycan that
A) never contains sugars such as glucose.
B) forms an unusual and flexible cell wall.
C) contributes to membrane stability.
D) may be present or absent dependent upon the temperature.

Answer 35

C) contributes to membrane stability.

The lipoglycan in Thermoplasma’s membrane contributes to its stability, particularly in the acidic environments where it thrives.

Question 36

Thermoproteotes whose optimal growth temperature is over 80°C are called
A) hyperthermophiles.
B) thermophiles.
C) extreme halophiles.
D) halophiles.

Answer 36

A) hyperthermophiles.

Thermoproteotes with optimal growth temperatures above 80°C are classified as hyperthermophiles.

Question 37

Hot sulfur-rich environments associated with terrestrial sulfur-rich springs are called
A) acid-mine drainage.
B) hydrothermal vents.
C) solfataras.
D) terrestrial volcanoes.

Answer 37

C) solfataras.

Solfataras are hot, sulfur-rich environments often associated with volcanic activity.

Question 38

T/F: Thus far, only Archaea have been found in the salt lakes, while Bacteria and Eukarya are noticeably absent.

Answer 38

False. While Archaea are often dominant in salt lakes, bacteria and even some eukaryotes (like Dunaliella) can also be found there.

Question 39

T/F: Replacing sodium with potassium can satisfy the requirement for sodium in the halobacteria

Answer 39

False. Potassium cannot fully replace the specific requirement for sodium in halobacteria. Sodium plays a crucial role in stabilizing cell walls and certain enzymes.

Question 40

T/F: Many halophiles require a high ionic environment for survival.

Answer 40

True. High ionic concentrations are essential for the survival of halophiles.

Question 41

T/F: The acetoclastic methanogens are mainly classified within one order.

Answer 41

True. Acetoclastic methanogens (those that use acetate) are primarily classified within the order Methanosarcinales.

Question 42

T/F: Some thermoproteota (crenarchaeotes) have growth optima above the boiling point of water (at atmospheric pressure).

Answer 42

True. Some Thermoproteota can grow at temperatures exceeding 100°C, the boiling point of water at standard pressure.

Question 43

T/F: Some species, mostly classified as Methanobacteriota, have archaeal histones that may contribute to DNA stability as well as having other functions.

Answer 43

True. Certain Methanobacteriota possess histone-like proteins that contribute to DNA stability and potentially other cellular functions.

Question 44

T/F: While many Archaea are bacilli or cocci, unusual morphologies such as square, flattened and irregular discs have also been identified in certain species.

Answer 44

True. Archaea exhibit a variety of cell shapes, including unusual morphologies like squares and irregular discs.

Question 45

T/F: Archaeal histones assist in maintaining the DNA in a double-stranded form at very high temperatures in species of Methanobacteriota.

Answer 45

True. Archaeal histones in some Methanobacteriota help maintain DNA stability at high temperatures.