MMG 421 - EXAM 3 QUESTIONS WITH
100% CORRECT ANSWERS LATEST
VERSION 2025/2026.
Chemolithotrophic bacteria and archaea obtain energy and electrons from inorganic sources -
ANS true
PMF refers to the process of e- shuttling from an e- donor to NAD+ - ANS false
protons
purple sulfur bacteria and green sulfur bacteria utilize H2S as e- donor in phototrophy, and as a
result produce elemental sulfur as a product of their photosynthesis, a process called
anoxygenic photosynthesis - ANS true
the redox potential (also called reduction potential) of an element participating in a respiration
metabolism represents its potential to donate e- in that metabolism, and is measured in units of
volts - ANS true
in reverse e- flow in a cell membrane, an e- originating from an external e- donor moves
towards a more electropositive e- acceptor - ANS false
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,electronegative instead of electropositive
reverse e- flow is required by many, if not most, chemolithotrophs other than hydrogen
oxidizers and is facilitated by PMF - ANS true
a dissimilatory metabolic rxn is one in which the metabolic end product of the redox rxn is
incorporated into microbial biomass - ANS false
assimilatory instead of dissimilatory
a mixotroph is a microorganism that utilizes an inorganic chemical for e- and energy, but an
organic source of C - ANS true
a bacterial cell is able to detect concentration gradients of chemicals over space (distance)
through tumble/run random-walk motion - ANS false
over time instead of over space
a high N:P ratio in the aquatic environments of cyanobacteria is favorable for nitrogen fixation
because of the high energy demand of this metabolism - ANS false
low N:P instead of high N:P
an e- acceptor in respirations, oxygen provides the least energy yield when coupled with any
given e- donor, compared to all other e- acceptors such as nitrate, Fe3+, sulfate, etc. -
ANS false
high energy yield instead of least energy yield
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, sulfide can be oxidized both aerobically and anaerobically to sulfate by microorganisms to
complete the sulfur cycle - ANS true
nitrifiers are microorganisms that reduce nitrate to nitrogen gas (via intermediates) under
anaerobic conditions. - ANS false
denitrifiers instead of nitrifiers
denitrifiers are microorganisms that oxidize ammonium to nitrate (via intermed) typically under
aerobic conditions - ANS false
nitrifiers instead of denitrifiers
nitrate can serve as an e- acceptor in anaerobic oxidation of methane and elemental sulfur,
thereby coupling nitrogen cycle transformations to booth the carbon and sulfur cycles via
microbial metabolisms - ANS true
anammox refers to anaerobic oxidation of ammonium to nitrogen gas by planctomycete
bacteria in the oceans with nitrate as e- acceptor, and represents a key mechanism for
transformation of ammonium in deep ocean water - ANS true
nitrogen fixation is a high energy yielding microbial metabolism, surpassing even aerobic,
oxidative respiration in gibbs free energy - ANS false
demanding instead of yielding
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
100% CORRECT ANSWERS LATEST
VERSION 2025/2026.
Chemolithotrophic bacteria and archaea obtain energy and electrons from inorganic sources -
ANS true
PMF refers to the process of e- shuttling from an e- donor to NAD+ - ANS false
protons
purple sulfur bacteria and green sulfur bacteria utilize H2S as e- donor in phototrophy, and as a
result produce elemental sulfur as a product of their photosynthesis, a process called
anoxygenic photosynthesis - ANS true
the redox potential (also called reduction potential) of an element participating in a respiration
metabolism represents its potential to donate e- in that metabolism, and is measured in units of
volts - ANS true
in reverse e- flow in a cell membrane, an e- originating from an external e- donor moves
towards a more electropositive e- acceptor - ANS false
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,electronegative instead of electropositive
reverse e- flow is required by many, if not most, chemolithotrophs other than hydrogen
oxidizers and is facilitated by PMF - ANS true
a dissimilatory metabolic rxn is one in which the metabolic end product of the redox rxn is
incorporated into microbial biomass - ANS false
assimilatory instead of dissimilatory
a mixotroph is a microorganism that utilizes an inorganic chemical for e- and energy, but an
organic source of C - ANS true
a bacterial cell is able to detect concentration gradients of chemicals over space (distance)
through tumble/run random-walk motion - ANS false
over time instead of over space
a high N:P ratio in the aquatic environments of cyanobacteria is favorable for nitrogen fixation
because of the high energy demand of this metabolism - ANS false
low N:P instead of high N:P
an e- acceptor in respirations, oxygen provides the least energy yield when coupled with any
given e- donor, compared to all other e- acceptors such as nitrate, Fe3+, sulfate, etc. -
ANS false
high energy yield instead of least energy yield
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, sulfide can be oxidized both aerobically and anaerobically to sulfate by microorganisms to
complete the sulfur cycle - ANS true
nitrifiers are microorganisms that reduce nitrate to nitrogen gas (via intermediates) under
anaerobic conditions. - ANS false
denitrifiers instead of nitrifiers
denitrifiers are microorganisms that oxidize ammonium to nitrate (via intermed) typically under
aerobic conditions - ANS false
nitrifiers instead of denitrifiers
nitrate can serve as an e- acceptor in anaerobic oxidation of methane and elemental sulfur,
thereby coupling nitrogen cycle transformations to booth the carbon and sulfur cycles via
microbial metabolisms - ANS true
anammox refers to anaerobic oxidation of ammonium to nitrogen gas by planctomycete
bacteria in the oceans with nitrate as e- acceptor, and represents a key mechanism for
transformation of ammonium in deep ocean water - ANS true
nitrogen fixation is a high energy yielding microbial metabolism, surpassing even aerobic,
oxidative respiration in gibbs free energy - ANS false
demanding instead of yielding
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
