C14 Sample Questions from Brock

Question 1

The metabolic diversity of photosynthetic bacteria stems from different
A) bacteriochlorophylls and pigments they contain.
B) chlorophylls they can have and organic compounds they can produce.
C) light-harvesting complexes, electron donors, and organic compounds they produce.
D) unrelated taxa capable of photosynthesis.

Answer 1

A) bacteriochlorophylls and pigments they contain.

Metabolic diversity in photosynthetic bacteria is largely influenced by the variety of bacteriochlorophylls and other pigments, which enable them to capture light energy across different wavelengths.

Question 2

Whether an organism is classified as a photoheterotroph or a photoautotroph depends on its
A) energy source.
B) carbon source.
C) oxygen requirements.
D) carbon and energy sources.

Answer 2

D) carbon and energy sources.

Classification into photoheterotroph (using light for energy but relying on external organic carbon sources) or photoautotroph (using light for energy and CO2 for carbon source) hinges on both energy and carbon source utilization.

Question 3

In photosynthesis, NADH and NADPH are produced from NAD + and NADP+ by
A) oxidation reactions.
B) reduction reactions.
C) both oxidation and reduction reactions.
D) neither oxidation nor reduction reactions.

Answer 3

B) reduction reactions.

NADH and NADPH are formed through the reduction of NAD+ and NADP+, respectively, indicating the gain of electrons (reduction).

Question 4

Bacteriochlorophyll and chlorophyll contain ________ as a cofactor.
A) iron (II)
B) iron (III)
C) magnesium
D) manganese

Answer 4

C) magnesium

Both bacteriochlorophyll and chlorophyll have magnesium at their molecular core, crucial for their light-absorbing properties.

Question 5

Which of the following is NOT a role of carotenoids?
A) as accessory pigments
B) photoprotection
C) to produce singlet oxygen
D) to quench toxic oxygen species

Answer 5

C) to produce singlet oxygen

Carotenoids are known for photoprotection (quenching excessive energy and preventing damage) and as accessory pigments, but they are not primarily involved in producing singlet oxygen; rather, they often protect against its damaging effects.

Question 6

Proteomic analysis of a microbial community indicated an abundance of phycobiliproteins. Which phototrophic group is likely active and abundant in this community?
A) cyanobacteria
B) eukaryotic phototrophs
C) green bacteria
D) prochlorophytes

Answer 6

A) cyanobacteria

Phycobiliproteins are characteristic light-harvesting pigments found predominantly in cyanobacteria and some eukaryotic algae.

Question 7

At some of the lowest light concentrations, ______ can still grow well due to their _______, which effectively harvest photons for energy.
A) green bacteria / antenna pigments
B) green bacteria / chlorosomes
C) purple bacteria / antenna pigments
D) purple bacteria / chlorosomes

Answer 7

B) green bacteria / chlorosomes

Green bacteria utilize chlorosomes, highly efficient light-harvesting structures, enabling growth at very low light intensities.

Question 8

Phycoerythrin is
A) the red phycobiliprotein.
B) the blue phycobiliprotein.
C) a type of carotenoid.
D) a green carotenoid.

Answer 8

A) the red phycobiliprotein.

Phycoerythrin is indeed known for its red fluorescence, a type of phycobiliprotein involved in light harvesting.

Question 9

Two separate photosystems involved in electron flow is a hallmark of
A) anoxygenic phototrophs.
B) green sulfur bacteria.
C) oxygenic phototrophs.
D) purple bacteria.

Answer 9

C) oxygenic phototrophs.

Oxygenic phototrophs, like plants and cyanobacteria, characteristically employ two photosystems (PSI and PSII) in linear electron flow, producing oxygen.

Question 10

Membrane vesicles known as chromatophores, which function in photosynthesis, are commonly found in
A) algae.
B) green sulfur bacteria.
C) most autotrophic organisms.
D) purple phototrophic bacteria.

Answer 10

D) purple phototrophic bacteria.

Chromatophores are specialized membrane vesicles involved in photosynthesis, typically found in purple bacteria.

Question 11

ʺSpecial pairʺ is the name given to the ______ in the photochemical complex of the purple bacteria.
A) two bacteriochlorophyll a molecules
B) two bacteriochlorophyll b molecules
C) two quinones
D) two reaction centers

Answer 11

A) two bacteriochlorophyll a molecules

The “special pair” refers to the closely associated pair of bacteriochlorophyll a molecules at the heart of the reaction center in purple bacteria.

Question 12

What will happen to a cyanobacterium that has its photosystem II (PSII) blocked?
A) Additional electron acceptors, such as NADP+, will be required to oxidize oxygen and overcome the lost PSII process.
B) Anoxygenic photosynthesis only using photosystem I (PSI) could occur by using cyclic photophosphorylation and an alternative electron donor such as H2
C) It will die from being unable to obtain energy for photosynthesis.
D) Photons will generate excessive reactive oxygen species and the cyanobacterium will die as a consequence.

Answer 12

B) Anoxygenic photosynthesis only using photosystem I (PSI) could occur by using cyclic photophosphorylation and an alternative electron donor such as H2

Blocking PSII would prevent linear electron flow, but cyanobacteria could potentially continue with cyclic photophosphorylation using PSI, albeit with different electron donors.

Question 13

Which group of microorganisms would the Calvin cycle LEAST likely be found in?
A) purple Bacteria
B) chemolithotrophic Bacteria
C) cyanobacteria
D) anoxygenic Chloroflexus

Answer 13

B) chemolithotrophic Bacteria

The Calvin cycle is a CO2 fixation pathway primarily associated with photoautotrophs and some chemoautotrophs that fix CO2; chemolithotrophs might use other fixation pathways or not fix CO2 at all.

Question 14

The process by which electrons from the quinone pool are forced against the thermodynamic gradient to reduce NAD+ to NADH is called reverse
A) proton motive force.
B) reduction.
C) electron transport.
D) energy flow.

Answer 14

A) proton motive force.

Reverse electron flow against the proton motive force gradient requires energy, often to reduce NAD+ to NADH in certain metabolic contexts.

Question 15

The path of electron flow in oxygenic phototrophs is referred to as the scheme.
A) E
B) S
C) Q
D) Z

Answer 15

D) Z

The Z scheme illustrates the linear electron flow from water to NADP+ in oxygenic photosynthesis, resembling the letter Z due to its shape on energy level diagrams.

Question 16

Plastocyanin is a
A) membrane-bound sac found in certain bacteria.
B) photosynthetic pigment found in some bacteria.
C) copper-containing protein in photosystem II that donates electrons to photosystem I.
D) blue-green bacterium known for its unusual photoreactive complex.

Answer 16

C) copper-containing protein in photosystem II that donates electrons to photosystem I.

Plastocyanin is a copper-containing electron carrier protein involved in transferring electrons from PSII to PSI in oxygenic photosynthesis.

Question 17

The Calvin cycle
A) is responsible for the fixation of CO2into cell material.
B) utilizes both NAD(P)H and ATP.
C) requires both ribulose bisphosphate carboxylase and phosphoribulokinase.
D) uses CO2, NAD(P)H, and ATP to make biomass with ribulose bisphosphate carboxylase and phosphoribulokinase.

Answer 17

D) uses CO2, NAD(P)H, and ATP to make biomass with ribulose bisphosphate carboxylase and phosphoribulokinase.

The Calvin cycle is a CO2 fixation pathway that utilizes NAD(P)H and ATP, involving key enzymes like ribulose bisphosphate carboxylase and phosphoribulokinase.

Question 18

Regarding CO2 fixation mechanisms in the autotrophic green sulfur bacteria,
A) Chlorobium uses the reverse citric acid cycle, and Chloroflexus uses the hydroxypropionate pathway.
B) Chlorobium uses the hydroxypropionate pathway, and Chloroflexus uses the reverse citric acid cycle.
C) both Chlorobium and Chloroflexus use the reverse citric acid cycle.
D) both Chlorobium and Chloroflexus use the hydroxypropionate pathway.

Answer 18

A) Chlorobium uses the reverse citric acid cycle, and Chloroflexus uses the hydroxypropionate pathway.

Chlorobium is known for using the reverse citric acid cycle, while Chloroflexus uses the 3-hydroxypropionate pathway.

Question 19

In most cases, the final product of sulfur oxidation is
A) hydrogen sulfide.
B) elemental sulfur.
C) sulfate.
D) thiosulfate.

Answer 19

C) sulfate.

Sulfate is the most common end product of sulfur oxidation in many sulfur-oxidizing bacteria.

Question 20

Identifying carboxysomes in a bacterium suggests it
A) contains the reverse citric acid cycle.
B) has a deficient Calvin cycle and accumulated CO2.
C) is in a carboxylic acid rich environment and is storing excess quantities for potentially harsh conditions.
D) will use the Calvin cycle to convert the concentrated into biomass.

Answer 20

D) will use the Calvin cycle to convert the concentrated CO2 into biomass.

Carboxysomes are organelles that contain RuBisCO and are involved in CO2 concentration for the Calvin cycle, indicating the bacterium uses this pathway for CO2 fixation.

Question 21

Ferrous iron (Fe2+) oxidation generally occurs in environments with
A) alkaline conditions.
B) high H+
C) high oxygen content.
D) little or no light present.

Answer 21

B) high H+.

Ferrous iron oxidation is often favored in acidic (high H+) environments, where Fe2+ is more soluble.

Question 22

Alternative autotrophic routes to the Calvin cycle such as the reverse citric acid cycle and the hydroxypropionate pathway are unified in their requirement for
A) CO2.
B) coenzyme A.
C) NAD(P)H.
D) organic compound(s) formed.

Answer 22

C) NAD(P)H.

Many alternative CO2 fixation pathways, like the reverse citric acid cycle and hydroxypropionate pathway, require reducing power in the form of NAD(P)H.

Question 23

The aerated upper layer of soil is likely to have ___________ concentrations of H2 for aerobic H2-oxidizing Bacteria, so these bacteria likely ________.
A) high / thrive in such conditions by not competing with chemoorganotrophs
B) high / generate important reducing equivalents as byproducts for other microorganisms in the soil
C) low / do not occur in such habitats
D) low / will need a chemoorganotrophic way to grow as well

Answer 23

C) low / do not occur in such habitats.

Aerated (oxygen-rich) environments, like the upper layer of soil, are less likely to have significant H2 concentrations due to rapid oxidation.

Question 24

What metabolic advantage do cells have in storing the elemental sulfur byproduct from sulfide oxidation?
A) The cells avoid producing transport energy waste to secrete the sulfur.
B) The byproduct serves as an electron reserve for subsequent oxidation.
C) Sulfur decreases the intracellular acidification for non-acid-tolerant sulfide oxidizers.
D) The byproduct can be used for other biosynthetic pathways that use sulfur, such as Rieske Fe-S proteins.

Answer 24

B) The byproduct serves as an electron reserve for subsequent oxidation.

Stored elemental sulfur can be oxidized later, providing electrons for energy production when other substrates are scarce.

Question 25

A cell that lacks sulfite reductase but can still oxidize sulfur for energy could be identified by
A) adenosine phosphosulfate reductase coupled with substrate-level phosphorylation.
B) electrons being transferred to cytochrome c prior to shuttling them into the electron transport chain.
C) identifying an alternative quinone, flavoprotein, or cytochrome.
D) quantifying the release of sulfate byproduct.

Answer 25

D) quantifying the release of sulfate byproduct.

Without sulfite reductase, sulfur oxidation would likely proceed directly to sulfate, measurable as an end product.

Question 26

The only organisms that perform photosynthesis are ones that produce some form of
A) chlorophyll or bacteriochlorophyll.
B) carotenoids.
C) phycoerythrin.
D) phycocyanin.

Answer 26

A) chlorophyll or bacteriochlorophyll.

These pigments are essential for absorbing light energy in all photosynthetic organisms.

Question 27

Which of the following are NOT found within the photosynthetic gene cluster of Rhodobacter (a purple phototrophic bacterium)?
A) genes encoding reaction center and light-harvesting photocomplexes
B) genes encoding proteins involved in phycobiliprotein biosynthesis
C) genes encoding proteins involved in bacteriochlorophyll biosynthesis
D) genes encoding proteins involved in carotenoid biosynthesis

Answer 27

B) genes encoding proteins involved in phycobiliprotein biosynthesis.

Rhodobacter, a purple bacterium, does not use phycobiliproteins (characteristic of cyanobacteria and some algae) for light harvesting.

Question 28

Anammox is an anaerobic process that generates energy from ______ and forms N2.
A) ammonia
B) ammonium
C) ammonia and nitrate
D) ammonia and nitrite

Answer 28

D) ammonia and nitrite.

Anammox bacteria convert ammonia and nitrite into nitrogen gas (N2) in the absence of oxygen.

Question 29

What would likely occur if an anammox bacterium was unable to use ladderane lipids?
A) Ammonium rather than ammonia would be used due to ammonia toxicity to other cellular processes within the anammoxosome.
B) It would require a different source for carbon assimilation.
C) Rates of anammox would be considerably slower due to a lack of localized metabolism.
D) Toxic products of the anammox reaction could kill the cell.

Answer 29

C) Rates of anammox would be considerably slower due to a lack of localized metabolism.

Ladderane lipids are crucial for the unique membrane structures in anammoxosomes, where the anammox reaction occurs; without them, the reaction rate would likely decrease.

Question 30

Which of the following reactions is classified as a heterofermentation?
A) hexose 2 lactate + 2 H+
B) HCOOH H2 + CO2
C) glucose lactate + ethanol + CO2 + H+
D) fructose 3 acetate + 3 H+

Answer 30

C) glucose → lactate + ethanol + CO2 + H+.

Heterofermentation involves the production of more than one type of product (e.g., lactate, ethanol, and CO2) from a single substrate (glucose).

Question 31

Glucose fermentation by Clostridium spp. produces ATP only when acetate and butyrate are produced. Why do these organisms produce acetone and butanol after strong initial activity of generating ATP with acetate and butyrate byproducts?
A) Acetate and butyrate accumulation creates a deadly acidic environment, which acetone and butanol do not.
B) Acetate and butyrate are no longer needed for biosynthetic pathways.
C) Acetone and butanol serve as better sources for NAD(P)+
D) Acetone and butanol production is favored for stability to store intracellular carbon sources for potential nutrient poor conditions.

Answer 31

D) Acetone and butanol production is favored for stability to store intracellular carbon sources for potential nutrient-poor conditions.

Shifting to acetone and butanol production allows for better survival during nutrient scarcity due to their stability and potential for later use.

Question 32

The foul-smelling putrescine byproduct suggests activity of
A) amino acid fermentation by clostridia.
B) secondary fermentation.
C) sulfur-oxidizing bacteria.
D) syntrophic carbohydrate metabolism.

Answer 32

A) amino acid fermentation by clostridia.

Putrescine, a foul-smelling compound, can be a byproduct of amino acid fermentation, particularly in clostridia.

Question 33

A bacterium that catabolizes a compound by linking ion pumps to establish a proton or sodium motive force for energy
A) can circumvent substrate-level and oxidative phosphorylation.
B) makes insufficient energy to grow but enough for cellular maintenance to survive.
C) requires a second bacterium to cooperatively drive the gradient.
D) still requires another carbon substrate to provide a carbon source.

Answer 33

A) can circumvent substrate-level and oxidative phosphorylation.

Using ion pumps can generate a proton or sodium motive force, enabling ATP synthesis without traditional substrate-level or oxidative phosphorylation mechanisms.

Question 34

Which metabolic strategy’s existence suggests rapid growth is NOT always the best strategy to survive in the environment?
A) anaerobic fermentation
B) disproportionation
C) methylotrophy
D) syntrophy

Answer 34

D) syntrophy.

Syntrophic relationships, where organisms cooperate for mutual metabolic benefit, often prioritize survival over rapid growth, highlighting the importance of cooperative strategies in certain environments.

Question 35

Obligate anaerobes can often use __________ electropositive redox couples than facultative anaerobes, and _______ metabolism is most common in this group as well.
A) lower / assimilative
B) lower / dissimilative
C) higher / assimilative
D) higher / dissimilative

Answer 35

B) lower / dissimilative.

Obligate anaerobes typically thrive in low-redox environments, using dissimilative (energy-yielding) metabolic processes with lower electropositive redox couples.

Question 36

In Bacteria, the most common oxidized form of nitrogen is ________ and of sulfur is ______.
A) nitrate / sulfate
B) nitrate / sulfite
C) nitrite / sulfate
D) nitrite / sulfite

Answer 36

A) nitrate / sulfate.

In many bacterial metabolic processes, nitrate is the common oxidized form of nitrogen, and sulfate is the common oxidized form of sulfur.

Question 37

Fermentation often produces CO2, which can be used by _________ as an electron acceptor for energy.
A) acetogens
B) methanotrophs
C) methanogens
D) acetogens and methanogens

Answer 37

D) acetogens and methanogens.

Both acetogens and methanogens can utilize CO2, albeit in different ways: acetogens reduce CO2 to acetate, while methanogens reduce CO2 to methane.

Question 38

How is ATP made by an acetogen during CO2 fixation?
A) Electrons from metal cofactors energize the electron transport chain and drive the proton motive force to activate ATP synthase.
B) Substrate-level phosphorylation of ADP occurs when coenzyme A is removed from acetyl-CoA.
C) It is made using substrate level phosphorylation and an ion motive force.
D) Acetyl CoA is produced from acetate and ATP is produced through substrate level phosphorylation.

Answer 38

B) Substrate-level phosphorylation of ADP occurs when coenzyme A is removed from acetyl-CoA.

Acetogens generate ATP through substrate-level phosphorylation during the conversion of acetyl-CoA to acetate.

Question 39

A researcher lacked the necessary equipment to measure methane production so instead monitored CO2 concentration as an unknown archaeon grew and produced methane. Why might CO2 NOT decrease while methane would still increase?
A) An alternative carbon source such as methanol was used.
B) CO2 is not a carbon source used by methanogens.
C) CO2 was used as an electron donor but not as a carbon substrate.
D) Methanogenic Archaea containing carboxysomes likely made measuring small losses of CO2 difficult to conclude.

Answer 39

C) CO2 was used as an electron donor but not as a carbon substrate.

If CO2 levels didn’t decrease, it might indicate CO2 was used in a manner not directly contributing to methane production, such as in electron donation.

Question 40

Methanogens that use methyl-CoM for biosynthesis use as a substrate.
A) acetate
B) carbon monoxide
C) methane
D) methanol

Answer 40

D) methanol.

Methyl-CoM is involved in the metabolism of methanol (among other substrates) in methanogens, leading to methane production.

Question 41

The serine pathway and ribulose monophosphate pathway can both be used by as a way to incorporate carbon into biomass.
A) acetogens
B) anoxygenic hydrocarbon fermenters
C) methanogens
D) methylotrophs

Answer 41

D) methylotrophs.

Methylotrophs, which grow on one-carbon compounds, can utilize various pathways for assimilating these compounds, including the serine and ribulose monophosphate pathways.

Question 42

What products would be expected to form during anoxic degradation of the seven-carbon compound benzoate following reduction and cleavage of the aromatic ring?
A) 1 three-carbon compound and 1 four-carbon compound
B) 1 three-carbon compound and 2 two-carbon compounds
C) 2 three-carbon compounds and CO2
D) 3 two-carbon compounds and CO2

Answer 42

D) 3 two-carbon compounds and CO2.

Under anoxic conditions, benzoate degradation typically involves reductive steps, leading to the cleavage of the seven-carbon aromatic ring into smaller fragments. A common outcome is the formation of three two-carbon compounds (e.g., acetate or similar short-chain compounds) and one molecule of CO2, reflecting the ring’s breakdown into these smaller units for energy harvesting.

Question 43

Organisms that aerobically catabolize methane use the intermediate for biosynthesis and produce when oxidizing the substrate for energy.
A) CH2O (formaldehyde) / CO
B) CH2O (formaldehyde) / CO2
C) HCOO−(formate) / CO
D) HCOO−(formate) / CO2

Answer 43

B) CH2O (formaldehyde) / CO2.

Aerobic methanotrophs initially convert methane to formaldehyde (CH2O), which can be used for biosynthesis, and ultimately produce CO2 as they fully oxidize methane for energy.

Question 44

Which of the following is the best potential reason that anoxic methane-oxidizing Archaea have not also acquired the ability to reduce sulfate?
A) Sulfate is toxic to these archaeans.
B) Having fewer metabolic capabilities decreases the archaeonʹs genome size and gives it flexibility to interact with other reducing bacteria, such as nitrate bacteria.
C) The archaeans are too rare to survive without the bacteria.
D) The methane-oxidizing Archaea are not capable of acquiring this metabolic capability.

Answer 44

B) Having fewer metabolic capabilities decreases the archaeon’s genome size and gives it flexibility to interact with other reducing bacteria, such as nitrate bacteria.

Specialization in anoxic methane oxidation might offer evolutionary advantages, such as reduced genome size and increased flexibility for symbiotic interactions, allowing these archaea to thrive in specific niches.

Question 45

What metabolism would be favored when there is a lack of electron acceptors?
A) fermentation
B) anoxygenic photosynthesis
C) anoxic ammonia oxidation
D) acetogenesis

Answer 45

A) fermentation.

In the absence of external electron acceptors (e.g., oxygen, nitrate, sulfate), fermentation is a favored metabolic strategy, as it allows organisms to generate energy through substrate-level phosphorylation or other mechanisms that don’t rely on external electron acceptors.

Question 46

T/F: The conversion of light into chemical energy is called photoautotrophy.

Answer 46

TRUE

Photoautotrophy is the process by which light energy is converted into chemical energy, typically in the form of ATP or NAD(P)H, in photosynthetic organisms.

Question 47

T/F: Some purple bacteria harvest light using bacteriochlorophylls.

Answer 47

TRUE

Purple bacteria utilize bacteriochlorophyll, a pigment that plays a crucial role in light harvesting, particularly in the reaction centers of purple bacteria.

Question 48

T/F: Reaction centers ONLY indirectly receive photon energy via light-harvesting molecules.

Answer 48

TRUE

Reaction centers are crucial for initiating photosynthesis, as they directly receive photon energy, converting it into chemical energy that drives the electron flow.

Question 49

T/F: Chlorosomes are present in purple bacteria but absent in green sulfur and green nonsulfur bacteria.

Answer 49

TRUE

Chlorosomes are organelles found in some photosynthetic bacteria, involved in the light-dependent synthesis of ATP.

Question 50

T/F: Carotenoids are hydrophobic accessory pigments and vary widely in the color they can absorb.

Answer 50

TRUE

Carotenoids serve as accessory pigments, helping to absorb light energy and transfer it to the reaction centers, where it’s used to initiate electron flow.

Question 51

T/F: Each chlorophyll and bacteriochlorophyll type is distinguished by its absorption spectrum.

Answer 51

TRUE

Different types of chlorophyll and bacteriochlorophyll have unique molecular structures, leading to distinct absorption spectra, which enable them to capture specific wavelengths of light.

Question 52

T/F: Photooxidation reactions can lead to the production of toxic forms of oxygen and the destruction of the photosynthetic apparatus.

Answer 52

TRUE

Photooxidation reactions involve the light-dependent formation of reactive oxygen species (ROS), which can damage the photosynthetic apparatus.

Question 53

T/F: The Calvin cycle provides autotrophs the ability to convert inorganic carbon into biomass and generate energy during this process.

Answer 53

TRUE

The Calvin cycle is a CO2 fixation pathway that utilizes NAD(P)H and ATP, generating energy for the autotroph.

Question 54

T/F: A bacterium that uses CO2 as an electron source but CANNOT use it as a carbon source is considered a mixotroph

Answer 54

TRUE

Mixotrophy involves using an external electron source (e.g., CO2) for energy, but relying on an internal or external organic compound for carbon, indicating an inability to use CO2 as a carbon source.

Question 55

T/F: Phototrophic purple bacteria such as Rhodobacter species are capable of nitrogen fixation.

Answer 55

FALSE

While some purple bacteria can fix nitrogen, this ability is not universal among phototrophic purple bacteria like Rhodobacter species, which primarily utilize light for energy.

Question 56

T/F: Despite being called the reverse citric acid cycle, this pathway is currently identified as the most ancient and widespread autotrophic pathway.

Answer 56

FALSE

The Calvin-Benson-Bassham (CBB) cycle is often considered the most widespread autotrophic pathway, whereas the reverse citric acid cycle, although ancient, is more limited in its distribution among autotrophs.

Question 57

T/F: Chemolithotrophs that obtain electrons from donors such as sulfide use the same electron transport chains to obtain energy as chemoorganotrophs.

Answer 57

FALSE

Chemolithotrophs utilizing inorganic electron donors (e.g., sulfide) often employ distinct electron transport chains adapted for inorganic substrates, differing from those used by chemoorganotrophs, which rely on organic compounds.

Question 58

T/F: Photosystem I is responsible for splitting a water molecule in the first step of oxygenic electron flow.

Answer 58

FALSE

In oxygenic photosynthesis, Photosystem II (PSII) is responsible for splitting water molecules (H2O) into oxygen (O2), electrons, and protons, marking the first step of oxygenic electron flow, not Photosystem I (PSI).

Question 59

T/F: RubisCO converts ribulose bisphosphate and CO2 into two molecules of 3-phosphoglyceric acid (PGA).

Answer 59

TRUE

RubisCO is an enzyme that catalyzes the conversion of ribulose bisphosphate and CO2, producing ATP.

Question 60

T/F: Organisms grown with CO2 as its sole carbon source must have energy in the form of ATP as well as reducing power.

Answer 60

TRUE

To fix CO2 into organic compounds, organisms need both energy (ATP) and reducing power (e.g., NADPH) to drive the carbon fixation process.

Question 61

T/F: Iron-oxidizing bacteria grow better in alkaline environments where protons are less likely to abiotically convert Fe2+ into Fe3+

Answer 61

FALSE

Iron-oxidizing bacteria typically thrive in acidic environments, where Fe2+ is more stable and can be more easily oxidized to Fe3+, generating energy.

Question 62

T/F: Some sulfur-oxidizing bacteria can simultaneously reduce nitrate, which enables them to grow anaerobically.

Answer 62

TRUE

Certain sulfur-oxidizing bacteria can use nitrate as an electron acceptor, allowing them to grow anaerobically by coupling sulfur oxidation with nitrate reduction.

Question 63

T/F: Due to a chemical equilibrium, a syntrophic relationship can be disrupted if the product from the first partnerʹs metabolism is removed too quickly.

Answer 63

TRUE

In syntrophic relationships, the balance of metabolites is crucial; rapid removal of a product can disrupt this balance, potentially halting the symbiotic process.

Question 64

T/F: Because H2 levels in oxic environments are transient, it is likely that aerobic hydrogen bacteria shift between chemoorganotrophy and chemolithotrophy depending on levels of organic compounds and hydrogen in their habitats.

Answer 64

TRUE

Given the transient nature of H2 in oxic environments, aerobic hydrogen bacteria likely adapt by switching between using H2 (chemolithotrophy) and organic compounds (chemoorganotrophy) for energy.

Question 65

T/F: Some anaerobic bacteria not only use organic compounds as a carbon source but can also use them for energy as well.

Answer 65

TRUE

Many anaerobic bacteria are capable of using organic compounds for both carbon assimilation and energy production through fermentation or anaerobic respiration.

Question 66

T/F: Heterofermentation CANNOT be differentiated from homofermentation based on the compound fermented.

Answer 66

TRUE

Differentiation between hetero- and homofermentation is based on the variety of products formed (multiple in heterofermentation, single in homofermentation), not the compound being fermented.

Question 67

T/F: A monooxygenase can always be distinguished from a dioxygenase by incorporating only one oxygen atom from O2 into the substrate rather than both.

Answer 67

TRUE

By definition, monooxygenases incorporate one O2 atom into the substrate, whereas dioxygenases incorporate both O2 atoms, making this a distinguishing feature.

Question 68

T/F: Reductive dechlorination involves chlorinated organic compounds serving as electron donors and releasing the chloride in inorganic forms.

Answer 68

FALSE

Reductive dechlorination typically involves chlorinated compounds serving as electron acceptors, with the release of chloride ions (inorganic form) as the compounds are dechlorinated.

Question 69

T/F: Fermentation of organic compounds can produce acetate.

Answer 69

TRUE

Acetate is a common product in various fermentation pathways, particularly in those involving the breakdown of carbohydrates or proteins.

Question 70

T/F: The acetyl-CoA pathway is a primary route for carbon source utilization.

Answer 70

TRUE

The acetyl-CoA pathway is indeed a central mechanism for utilizing carbon sources, especially in autotrophic microorganisms that fix CO2 into acetyl-CoA.

Question 71

T/F: When elemental sulfur is provided externally as an electron donor, the organism must attach itself to the sulfur particle because of the extreme insolubility of elemental sulfur

Answer 71

TRUE

Due to elemental sulfur’s insolubility, organisms using it as an electron donor often must be in direct contact with the sulfur particles to facilitate electron transfer.

Question 72

T/F: One result of the oxidation of reduced sulfur compounds is a rise in the pH of the medium.

Answer 72

FALSE

Oxidation of reduced sulfur compounds typically produces sulfuric acid (H2SO4) as a byproduct, leading to a decrease in pH (more acidic conditions), not an increase.

Question 73

T/F: Bacteria that are capable of oxidizing both iron and sulfur usually have a strong preference for sulfur oxidation because it yields more energy.

Answer 73

FALSE

The preference between iron and sulfur oxidation for energy production can vary among bacteria, depending on environmental conditions and the specific metabolic pathways involved.

Question 74

T/F: Beta-oxidation exclusively removes two carbons at a time to catabolize fatty acids regardless of the carbon chain length

Answer 74

TRUE

Beta-oxidation is a process that systematically shortens fatty acid chains by removing two-carbon units (acetyl-CoA) in each cycle, applicable to fatty acids of various lengths.

Question 75

T/F: Bacteria that degrade aromatic compounds with reductions steps rather than oxygenase activity prior to ring fission are likely to be anaerobes

Answer 75

TRUE

The use of reduction steps before ring fission in aromatic compound degradation is characteristic of anaerobic metabolic pathways, as oxygenases typically require oxygen to initiate ring breakdown.