MICROBIOLOGY EXAM 2 PRACTICE TEST 2026
QUESTIONS WITH CORRECT ANSWERS
GRADED A+
◉ Redox reactions refer to a pair of reactions in which a particular
oxidation is coupled to a corresponding reduction.Although neither
can occur independently of the other, it can be helpful to write each
oxidation or reduction as a half reaction to help us understand & to
calculate the flow of energy.In this exercise, sort each listed half
reaction as either an oxidation or a reduction. Answer: Oxidation:
H2 → 2H+ + 2e-
HS- → S0 + 2H+ + e-
NADH + H+ → NAD+ + 2H+ + 2e-
Ca0 → Ca+2 + 2e-
Reduction:
½O2 + 2H+ + 2e- → H2O
,FAD + 2H+ + 2e- → FADH2
Fe3+ + e- → Fe2+
acetaldehyde + 2e- + 2 H+ → ethanol
◉ What process is illustrated by the diagram below?
A. fermentation
B. reverse electron flow
C. anaerobic respiration
D. aerobic respiration
E. glycolysis Answer: D. aerobic respiration
◉ Table 14.1 is called the "electron tower" & it is a convenient way
of organizing biologically important redox pairs.All of the half
reactions are written as reductions in the Table.Reactions with the
most negative reduction potentials (E°') & positive standard free
energy changes (ΔG°') are at the top,while those reactions with the
most positive E°' & most negative ΔG°' values are at the bottom.This
means that the reduced forms of the couples (in the blue column)
near the top are good electron donors,while the oxidized forms of
redox pairs (in the red column) near the bottom are good electron
acceptors.
Use the values in the chart above to estimate whether a bacterium
could grow by oxidizing NO2- to NO3- when using elemental sulfur
(S0) as a terminal electron acceptor. Choose one:
A. Yes, because the ΔG°' of the combined reaction would be positive.
,B. No, because the ΔG°' of the combined reaction would be negative.
C Answer: C. No, because the ΔG°' of the combined reaction would be
positive.
◉ Consider the case of Acidothiobacillus ferridoxans, an acidophilic
iron oxidizer that obtains energy from the oxidation of ferrous iron
(Fe2+) to ferric iron (Fe3+) at pH 2.Under these conditions, the E°' of
the Fe3+/Fe2+ redox pair is extremely electropositive (+770 mV),
close to the E°' of the half O2/H2O pair (+820 mV).You can see that
very little potential energy is to be gained from iron oxidation when
there are equimolar concentrations of reactants & products.In
reality, A. ferridoxans is restricted to iron-rich habitats such as acid-
mine-drainage streams.Iron oxidizers can be successful in these
environments because a ten-fold ratio of reactants to products . . .
Choose one:
A. increases the E°' by 60 mV per electron.
B. decreases the E°' by 60 mV per electron.
C. decreases the E°' by 60 mV per proton.
D. increases the E°' by 60 mV per proton. Answer: A. increases the
E°' by 60 mV per electron.
◉ In a typical Gram-negative bacterium such as E. coli, proteins
known as cytochromes (which are sometimes part of larger
complexes known as oxidoreductases) are localized to the Answer:
inner plasma membrane
, ◉ Energy from cellular metabolism is converted to ATP by respiring
organisms.Place the following steps in the correct order. Answer: 1)
Glycolysis and TCA cycle generate NADH & FADH
2) NADH and FADH are oxidized by electron transport proteins
3) Electron transport releases energy that is used to translocate H+
4) An electrochemical gradient of protons is established (delta p)
5) Influx of H+ through ATP synthase drives ATP production
◉ The intracellular concentration of sodium ions in E. coli is about
10 mM. If an E. coli sample is placed into a solution with a sodium
concentration of 100 mM and a sodium ionophore is added, what
happens to the cells' ability to create ATP via ATP synthase?
Choose one:
A. ATP synthesis capacity increases because the Δp becomes more
negative due to a more negative Δψ.
B. ATP synthesis capacity decreases because the Δp becomes less
negative due to a less negative Δψ.
C. ATP synthesis capacity decreases because the Δp becomes more
negative due to an increased ΔpH.
D. ATP synthesis capacity decreases because the Δp becomes less
negative due to a decreased ΔpH. Answer: B. ATP synthesis capacity
decreases because the Δp becomes less negative due to a less
negative Δψ.
QUESTIONS WITH CORRECT ANSWERS
GRADED A+
◉ Redox reactions refer to a pair of reactions in which a particular
oxidation is coupled to a corresponding reduction.Although neither
can occur independently of the other, it can be helpful to write each
oxidation or reduction as a half reaction to help us understand & to
calculate the flow of energy.In this exercise, sort each listed half
reaction as either an oxidation or a reduction. Answer: Oxidation:
H2 → 2H+ + 2e-
HS- → S0 + 2H+ + e-
NADH + H+ → NAD+ + 2H+ + 2e-
Ca0 → Ca+2 + 2e-
Reduction:
½O2 + 2H+ + 2e- → H2O
,FAD + 2H+ + 2e- → FADH2
Fe3+ + e- → Fe2+
acetaldehyde + 2e- + 2 H+ → ethanol
◉ What process is illustrated by the diagram below?
A. fermentation
B. reverse electron flow
C. anaerobic respiration
D. aerobic respiration
E. glycolysis Answer: D. aerobic respiration
◉ Table 14.1 is called the "electron tower" & it is a convenient way
of organizing biologically important redox pairs.All of the half
reactions are written as reductions in the Table.Reactions with the
most negative reduction potentials (E°') & positive standard free
energy changes (ΔG°') are at the top,while those reactions with the
most positive E°' & most negative ΔG°' values are at the bottom.This
means that the reduced forms of the couples (in the blue column)
near the top are good electron donors,while the oxidized forms of
redox pairs (in the red column) near the bottom are good electron
acceptors.
Use the values in the chart above to estimate whether a bacterium
could grow by oxidizing NO2- to NO3- when using elemental sulfur
(S0) as a terminal electron acceptor. Choose one:
A. Yes, because the ΔG°' of the combined reaction would be positive.
,B. No, because the ΔG°' of the combined reaction would be negative.
C Answer: C. No, because the ΔG°' of the combined reaction would be
positive.
◉ Consider the case of Acidothiobacillus ferridoxans, an acidophilic
iron oxidizer that obtains energy from the oxidation of ferrous iron
(Fe2+) to ferric iron (Fe3+) at pH 2.Under these conditions, the E°' of
the Fe3+/Fe2+ redox pair is extremely electropositive (+770 mV),
close to the E°' of the half O2/H2O pair (+820 mV).You can see that
very little potential energy is to be gained from iron oxidation when
there are equimolar concentrations of reactants & products.In
reality, A. ferridoxans is restricted to iron-rich habitats such as acid-
mine-drainage streams.Iron oxidizers can be successful in these
environments because a ten-fold ratio of reactants to products . . .
Choose one:
A. increases the E°' by 60 mV per electron.
B. decreases the E°' by 60 mV per electron.
C. decreases the E°' by 60 mV per proton.
D. increases the E°' by 60 mV per proton. Answer: A. increases the
E°' by 60 mV per electron.
◉ In a typical Gram-negative bacterium such as E. coli, proteins
known as cytochromes (which are sometimes part of larger
complexes known as oxidoreductases) are localized to the Answer:
inner plasma membrane
, ◉ Energy from cellular metabolism is converted to ATP by respiring
organisms.Place the following steps in the correct order. Answer: 1)
Glycolysis and TCA cycle generate NADH & FADH
2) NADH and FADH are oxidized by electron transport proteins
3) Electron transport releases energy that is used to translocate H+
4) An electrochemical gradient of protons is established (delta p)
5) Influx of H+ through ATP synthase drives ATP production
◉ The intracellular concentration of sodium ions in E. coli is about
10 mM. If an E. coli sample is placed into a solution with a sodium
concentration of 100 mM and a sodium ionophore is added, what
happens to the cells' ability to create ATP via ATP synthase?
Choose one:
A. ATP synthesis capacity increases because the Δp becomes more
negative due to a more negative Δψ.
B. ATP synthesis capacity decreases because the Δp becomes less
negative due to a less negative Δψ.
C. ATP synthesis capacity decreases because the Δp becomes more
negative due to an increased ΔpH.
D. ATP synthesis capacity decreases because the Δp becomes less
negative due to a decreased ΔpH. Answer: B. ATP synthesis capacity
decreases because the Δp becomes less negative due to a less
negative Δψ.
