Week 7

Question 1

Which of the following best explains why E. coli prefers aerobic respiration over anaerobic respiration when oxygen is available?
A) ATP yield is higher due to a more efficient electron transport chain
B) Oxygen directly provides energy for ATP synthesis
C) Fermentation produces more reducing power than respiration
D) Anaerobic respiration prevents substrate-level phosphorylation

Answer 1

Answer: A
Explanation: Oxygen serves as the final electron acceptor in aerobic respiration, producing the highest ATP yield. The electron transport chain in aerobic conditions is more efficient, allowing E. coli to generate more energy compared to anaerobic respiration.

Question 2

Why do chemolithotrophs require additional pathways like the Calvin cycle to grow?
A) They lack the ability to use organic molecules for energy
B) Inorganic electron donors do not provide carbon for biosynthesis
C) They produce more reducing power than they consume
D) Electron transport in chemolithotrophs bypasses ATP generation

Answer 2

Answer: B
Explanation: Chemolithotrophs obtain energy from inorganic molecules but still require carbon to build cellular components. Since their electron donors (e.g., Fe²⁺, NO₂⁻) do not contain carbon, they rely on CO₂ fixation pathways like the Calvin cycle.

Question 3

In what situation would a microorganism rely on fermentation instead of respiration, despite the presence of a terminal electron acceptor like NO₃⁻?
A) When the proton motive force cannot be maintained
B) When glucose is not available as an energy source
C) When the electron acceptor is not efficiently reduced
D) When ATP levels are already high

Answer 3

Answer: A
Explanation: If the organism cannot efficiently transfer electrons to NO₃⁻ (due to enzyme limitations or unfavorable redox potential), it will switch to fermentation, which regenerates NAD⁺ without using an external electron acceptor.

fermentation and respiration both regenerate NAD+ in different ways , No3 is part of the ETC,

Question 4

What is a primary advantage of bacteriorhodopsin-driven phototrophy compared to chlorophyll-based photosynthesis?
A) It does not require an electron transport chain
B) It produces more ATP per photon absorbed
C) It captures light across a broader spectrum of wavelengths
D) It generates more reducing power for biosynthesis

Answer 4

Answer: A
Explanation: Bacteriorhodopsin acts as a light-driven proton pump, generating a proton gradient directly without needing an electron transport chain. This makes it a simpler and efficient system in some archaea.

Question 5

When does fermentation occur? What cellular processes are involved?

Answer 5

Occurs when there is no oxygen and there is an abundance of sugars. ETC is not involved but glycolysis is involved

Question 6

Which of the following is true for fermentation?
A. The final electron acceptor is an inorganic molecule
B. The final electron acceptor is an organic molecule
C. The final electron acceptor is pyruvate
D. The final eletron acceptor is NADH

Answer 6

The final electron acceptor is an organic molecule such as pyruvate
b and c

Question 7

What is the difference of the strutures of pyruvate and lactate/

Answer 7

Pyruvate had a carbonyl group and lactate has an alcohol group

(Carbonyl is reduced to an alcohol)

Pyruvate + NADH —> Lactate + NADH+

Question 8

What process produces lactic acid?
A. Glycolysis
B. ETC

Answer 8

Glycolysis

Question 9

What is common beween fermentation and respiration? And whats different between the two

Answer 9

Common: both processes oxidize NADH to regenerate NAD+

Differences: respiration (glycolysis + CAC + oxidative phosphorylation) conserves more energydue to oxidative phosphorylation and creates way more ATP

both regenerate NAD+ in different ways

Question 10

Are inorganic electron donors such as H2, H2S, Fe2+, NH4+, etc, capable of conducting fermentation? Then List the organism type

Answer 10

No, thhey cannot. These organisms do not possess organic molecules like glucose to undergo fermentarion.These organisms are chemolithotrophs

Question 11

What are organic electron donors (chemiorganotrophs) capable of (in terms of cellular processes)

Answer 11

Fermentation, anaerobic respiration, and aerobic respiration

Question 12

What is the difference if an electron donor is not h20 and if the electron donor is h20 in phototrophs?

Answer 12

H20 electron donors undergo oxygenic photosynthesis

Non h20 electron donors undergo anoxygenic photosynthesis

Question 13

What does light provide?
A. Aerobic respiration and PMF
B. Anaerobic respiration and PMF
C. Electron transport and PMF

Answer 13

Light provides energy for electron transport and generates the PMF

Question 14

Why is oxygen considered the most efficient terminal electron acceptor in microbial metabolism?
A) Oxygen has the highest reduction potential, allowing the greatest energy yield from electron transfer
B) Oxygen generates ATP directly by acting as an energy source in oxidative phosphorylation
C) Oxygen is required for all forms of metabolism, including fermentation and anaerobic respiration
D) Oxygen prevents the need for proton motive force (PMF) by accepting electrons without forming water

Answer 14

Oxygen is the best because its conversion to water yields the greatest gibbs free energy

Oxygen has the highest reduction potential

Question 15

What is a key difference between the final stage of aerobic and anaerobic respiration?
A) In aerobic respiration, the last cytochrome transfers electrons to O₂, while in anaerobic respiration, nitrogen reductase transfers electrons to NO₃⁻ or other acceptors
B) Anaerobic respiration does not use a cytochrome system, whereas aerobic respiration does
C) Aerobic respiration generates fewer protons per electron transferred than anaerobic respiration
D) Anaerobic respiration produces more ATP because nitrogen reductase is more efficient than cytochrome oxidase

Answer 15

Explanation: In aerobic respiration, the final cytochrome (cytochrome oxidase) transfers electrons to O₂, forming water (H₂O). In anaerobic respiration, nitrate reductase (or other reductases) transfers electrons to NO₃⁻, reducing it to NO₂⁻, N₂O, or N₂. Aerobic respiration generally generates more protons across the membrane, leading to a higher proton motive force (PMF) and ATP yield than anaerobic respiration.

Question 16

What is the difference between the final electron acceptors in aerobic respiration and anaerobic respiration?

Answer 16

Aerobic uses oxygen as a final electron acceptor usinf cytochrome bo3, and lots of energy is generated, and protons ae produced

Anaerobic respiration uses enzyme nitrogen reductase to reduce NO3-, no extra protons produced, and less energy is produced

Question 17

Why do some bacteria preferentially use the reductive TCA cycle over the Calvin cycle for carbon fixation?
A) It requires less ATP per molecule of CO₂ fixed
B) It does not require NADPH for reducing power
C) It generates more intermediates for biosynthesis
D) It is better suited for high-oxygen environments

Answer 17

Answer: A
Explanation: The reductive TCA cycle is more ATP-efficient than the Calvin cycle, making it preferable in energy-limited environments. It allows some chemolithoautotrophs to fix carbon while using less energy.

Question 18

What would happen if a nitrogen-fixing bacterium had a defective nitrogenase enzyme?
A) It would switch to using nitrate (NO₃⁻) as a nitrogen source
B) It would be unable to grow even if ammonia (NH₃) were available
C) It would increase oxygen consumption to compensate
D) It would rely on fermentation to regenerate reducing power

Answer 18

Answer: A
Explanation: Nitrogenase is essential for converting N₂ into biologically usable ammonia. If it were defective, the bacterium would need to rely on an alternative nitrogen source like nitrate or ammonia from the environment.

Question 19

What is the most likely reason anoxygenic phototrophs evolved to use sulfur (S²⁻) instead of water (H₂O) as an electron donor?
A) Oxygen is a toxic byproduct of water oxidation
B) Sulfur provides a higher redox potential for ATP synthesis
C) Water oxidation requires more complex enzymatic pathways
D) Sulfur donates electrons directly to NAD(P)+ for biosynthesis

Answer 19

Water oxidation requires more complex enzyme pathways

Explanation: Splitting water into oxygen and protons is an energetically demanding process requiring photosystem II. Anoxygenic phototrophs evolved a simpler system using sulfur compounds, which are easier to oxidize.

Question 20

What would happen if an organism using the Calvin cycle had a defective RuBisCO enzyme?
A) CO₂ fixation would halt completely
B) The cell would switch to using organic carbon sources
C) More ATP would be required to complete the cycle
D) Oxygen would accumulate, disrupting redox balance

Answer 20

Answer: B
Explanation: RuBisCO is essential for fixing CO₂ in the Calvin cycle. If defective, the cell would need to switch to heterotrophic metabolism, relying on organic carbon sources instead.

Question 21

What distinguishes the assimilation of sulfate (SO₄²⁻) from nitrate (NO₃⁻) in bacterial metabolism?
A) Sulfate must be reduced to H₂S before incorporation into biomolecules
B) Nitrate is more energy-intensive to assimilate than sulfate
C) Both require an electron donor, but sulfate assimilation produces ATP
D) Nitrate is directly incorporated into amino acids, whereas sulfate is not

Answer 21

Answer: A
Explanation: Sulfate must first be reduced to H₂S through assimilatory sulfate reduction before being incorporated into amino acids like cysteine. Nitrate, in contrast, can be reduced to ammonia and directly used.

Question 22

If a bacterium is growing in a nutrient-rich environment but has no access to oxygen or nitrate, what will most likely happen?
A) It will switch to anaerobic respiration using sulfate as an electron acceptor
B) It will increase fermentation rates to generate ATP
C) It will undergo oxidative stress due to electron accumulation
D) It will use alternative electron donors like hydrogen gas (H₂)

Answer 22

Answer: B
Explanation: Without oxygen or nitrate, the bacterium cannot use respiration and will rely on fermentation, which regenerates NAD⁺ to sustain glycolysis and ATP production.

Question 23

A term used for an organism that obtains its reducing power from oxidation or inorganic molecules, almost all are extremophiles:
A. Chemoorganotrophs
B. Chemolithotrophs
C. Phototrpohs

Answer 23

Chemolithotrophs

Question 24

Iron oxide is present in chemolithotrophs. Iron oxide is insoluble and cannot be transported inside of the cell. How will the bacteria oxidize iron?
A. Using electrically conductive flagella
B. Using electrically conductive pili

Answer 24

Using electrically conductive pilli (final electron acceptor is outside of the cell, electrons travel through conductive pilli to reduce iron oxide minerals)

Question 25

What does oxygenic photosynthesis, anoxygenic photosynthesis, and nonhotosynthetic phototrophs use to function?

Answer 25

Oxy = use water as an electron donor to make O2 Anoxygenic = uses sulfide as an electron donor to make sulfate Nonphotosynthetic= use bacteriorhodopsin (enzyme) to generate a PMF

Question 26

A student has written the following: “ATP is enzymatically synthesized by the αβ subunits of the ATP synthase when electrons are flowing into the cell, but it could also be hydrolyzed in the reverse direction.” What is your assessment of their answer? A. The statement is true B. The statement would be true if “αβ subunits” were changed to “ac12 subunits” C. The statement would be true if the word “electrons” were changed to “protons” D. None of the above

Answer 26

correct: C protons flow into the cell (the intermembrane space) - electrons flow through the membrane - Abeta subunits changing to ac12 units is still true

Question 27

Which of the following enzymes is found in E. coli when it is growing in soil (where it is exposed to light and air)? A. Cytochrome C B. Nitrate reductase C. Lactate dehydrogenase (converts pyruvate to lactate) D. Cytochrome bo3

Answer 27

Cytochrome bo3 - cytochrome c is not found in ecoli - b uses nitrate reductase for anaerobic conditions - c is used for fermentation

Question 28

A scientist is conducting an experiment where they put E. coli in a flask containing media with glucose and essential nutrients but no nitrate. The scientist then replaces the air in the flask with nitrogen gas and seals the flask with parafilm, which is flexible but not permeable to gas. They then incubate the flask for two days at 37° C. When the scientist returns to analyze what happened to the flask, which of the following scenarios did they see?

Answer 28

cloudy=growth occurs parafilm budgling = fermentation creates gas, expands parafilm fermentation has occured because no oxygen or nitrate is present , therefore C is the correct option

Question 29

The TCA cycle operates in: A. Aerobic respiration B. Fermentation C. Anaerobic respiration D. Aerobic and anaerobic respiration E. All of the above

Answer 29

solution D. Tca cycle does not operate during fermentation (fermentation is not glycolysis) *tca cycle uses pyruvate, acetyl-coa, and NAD+ although all processes useémake NAD+, fermentation is the only option that regenerates NAD+ without the TCA cycle since fermentation gets NAD+ directly from oxidizing pyruvate

Question 30

is fermentation the same as glycolysis? why or why not? what are the similarities and differences?

Answer 30

no they do not mean the same thing. fermentation - regenerates NAD+ to keep glycolysis running - produces no atp - anaerobic conditions - makes lactic acid or lactate, ethanol and CO2 in yeast glycolysis : - breaks down glucose into pyruvate and makes ATP - makes 2 ATP - makes pyruvate, NADH, and ATP

Question 31

how are fermentation and glycolysis connected?

Answer 31

fermentation depends on glycolysis to supply pyruvate and NADH

Question 32

how do the usage of pyruvate differ in glycolysis and fermentation

Answer 32

fermentation uses pyruvate as a final electron acceptor to make lactate, pyruvate is also an intermediate glycolysis makes pyruvate as one of its products, which can be used to make many different molecules

Question 33

If Paracoccus ended up with a mutation in Complex 1 that made the protein(s) non-functional, what would the bacteria most likely use as a final electron acceptor? A.Oxygen B.Nitrate C.Lactate D.All of the above E.None of the above

Answer 33

oxygen bc you can still get electrons from complex 2 - not nitrate bc paracoccus is not ecoli and does not use nitrate, paracoccus only does aerobic respiration - not lactate because paracoccus is aerobic and does not undergo fermentation

Question 34

A chemolithotroph that uses aerobic respiration is most likely to use: A. H2 as an energy source and electron donor B. Sunlight as an energy source and H2 as an electron donor C. Glucose as an energy source and electron donor D. Sunlight as an energy source and glucose as an electron donor E. All of the above

Answer 34

A

Question 35

Is it possible for an aerobe to grow using only glycolysis (i.e. stopping at pyruvate)? A. Yes, because all amino acids and nucleotides can be made from intermediates of glycolysis B. Yes, because glycolysis produces ATP C. No, because the pool of oxidized NAD+ would get used up D. No, because oxidative phosphorylation is required to help cells deal with oxygen

Answer 35

the answer is C because glycolysis needs NAD+ to be regenerating via fermentation (fermentation needs pyruvate) stopping at pyruvate means no fermentation, which means no ETC or fermentation in anerobes. glycolysis will stop when NAD+ is reduced to NADH, making continued atp production impossible

Question 36

A student has written the following statement on an exam: “Bacteria that use anaerobic respiration use a terminal electron acceptor that is not oxygen because oxygen is toxic to these bacteria.” What is your assessment of the student’s statement? A. The statement is correct B. The statement would be correct if the word “not” were removed C. The statement would be correct if the word “oxygen” were replaced with nitrate D. None of the above

Answer 36

none of the above because - ocygen is tocxic is an incorrect statement - the question is not specific to bacteria metabolism type - not true for ALL bacteria that are anaerobic find that oxygen is toxic to them

Question 37

An oxygenic phototroph uses: A. Light to generate NADH and electrons from water to make complex molecules B. Light to generate NADH and electrons from oxygen to make complex molecules C. Light to generate ATP and electrons from water to make complex molecules D. Light to generate ATP and electrons from oxygen to make complex molecules

Answer 37

c

Question 38

Bacteria that use H2S as an electron source could be: A. Chemolithotrophs B. Anoxygenic phototrophs C. Both A and B D. Neither A nor B

Answer 38

both

Question 39

Bacteriorhodopsin: A. Is the first step in the electron transport chain in some archaea B. Uses accessory pigments like β-carotene to capture light C. Converts the energy from photons to proton motive force through isomerization of retinal D. All of the above

Answer 39

Converts the energy from photons to proton motive force through isomerization of retinal incorrect: a-not necessarily b-does not use b-carotene

Question 40

Which of the following statements about ribulose-1,5- bisphosphate is true? A. It is a precursor for the synthesis of ATP B. It is used and then regenerated in the Calvin cycle C. It can be found in the carboxysome D. All of the above

Answer 40

It is used and then regenerated in the Calvin cycle C. It can be found in the carboxysome

Question 41

Nitrogen assimilation, specifically the fixation of N₂ to NH₃ by nitrogenase, requires a high ATP input. What is the primary reason for this high energy demand? A. Breaking the triple bond in N₂ requires a significant amount of energy input due to its high bond dissociation energy. B. The process occurs in anaerobic conditions, requiring ATP to compensate for the absence of oxidative phosphorylation. C. Nitrogenase must actively pump protons to generate a proton motive force, which is essential for NH₃ production. D. The reduction of NH₃ to amino acids is an endergonic reaction that must be continuously driven by ATP hydrolysis.

Answer 41

Breaking the N≡N triple bond requires significant energy because it is one of the strongest chemical bonds in nature, making nitrogen fixation highly ATP-intensive.

Question 42

Which of the following amino acids is not made from pyruvate? A. Valine B. Alanine C. Aspartate D. Histidine

Answer 42

histidine, it is synthesized in the pentose phosphate pathway aspartate comes from oxaloacetate (from pyruvate) Valine (amino acid chaing derived from pyruvate)

Question 43

Which pathway is directly responsible for synthesis of 5, 7, and 8 carbon sugars found in bacterial LPS and capsules? A. Reductive TCA cycle B. Pentose phosphate pathway C. Glycolysis D. Calvin cycle

Answer 43

pentose phosphate pathway because it is reponsible for sugar arrangement