Fermentation (anaerobic respiration) MCQs With Answer

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Fermentation (anaerobic respiration) MCQs With Answer

Fermentation, a form of anaerobic respiration, is vital for B. Pharm students to understand energy metabolism, redox balance, and bioprocessing. This concise guide covers core concepts — glycolytic flux, pyruvate fates, NAD+/NADH regeneration, key enzymes (lactate dehydrogenase, pyruvate decarboxylase), and differences between fermentation and anaerobic respiration using alternate electron acceptors. It also links microbial fermentation types, industrial applications (ethanol, lactic acid, antibiotics), ATP yield, and physiological relevance in hypoxic tissues. These targeted points help bridge biochemistry with pharmaceutical manufacturing and clinical implications. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary purpose of fermentation in cells?

  • To generate large amounts of ATP by oxidative phosphorylation
  • To regenerate NAD+ from NADH so glycolysis can continue
  • To fully oxidize glucose to CO2 and H2O
  • To synthesize amino acids from pyruvate

Correct Answer: To regenerate NAD+ from NADH so glycolysis can continue

Q2. Which enzyme catalyzes the conversion of pyruvate to lactate in homolactic fermentation?

  • Pyruvate dehydrogenase
  • Lactate dehydrogenase
  • Pyruvate carboxylase
  • Alcohol dehydrogenase

Correct Answer: Lactate dehydrogenase

Q3. How many net ATP molecules are produced per glucose molecule during typical fermentation from glycolysis?

  • 36 ATP
  • 2 ATP
  • 30 ATP
  • 0 ATP

Correct Answer: 2 ATP

Q4. Which product is characteristic of alcoholic fermentation performed by Saccharomyces species?

  • Lactic acid
  • Ethanol and CO2
  • Propionic acid
  • Acetone and isopropanol

Correct Answer: Ethanol and CO2

Q5. In fermentation, what is the immediate electron acceptor that allows NADH oxidation?

  • Oxygen
  • Pyruvate or its derivatives
  • Nitrate
  • Sulfate

Correct Answer: Pyruvate or its derivatives

Q6. Which statement best distinguishes fermentation from anaerobic respiration?

  • Fermentation uses external inorganic electron acceptors like nitrate; anaerobic respiration does not
  • Fermentation involves substrate-level phosphorylation only; anaerobic respiration uses an electron transport chain with alternate acceptors
  • Both processes produce identical ATP yields
  • Anaerobic respiration occurs only in eukaryotes

Correct Answer: Fermentation involves substrate-level phosphorylation only; anaerobic respiration uses an electron transport chain with alternate acceptors

Q7. Which pathway is the source of pyruvate that enters fermentation?

  • Citric acid cycle
  • Glycolysis (Embden-Meyerhof pathway)
  • Pentose phosphate pathway
  • β-oxidation of fatty acids

Correct Answer: Glycolysis (Embden-Meyerhof pathway)

Q8. Which product is typical of heterolactic fermentation?

  • Only lactic acid
  • Lactic acid, ethanol, and CO2
  • Butyric acid only
  • Acetone and ethanol only

Correct Answer: Lactic acid, ethanol, and CO2

Q9. The enzyme pyruvate decarboxylase requires which cofactor in alcoholic fermentation?

  • Biotin
  • Thiamine pyrophosphate (TPP)
  • NADP+
  • FAD

Correct Answer: Thiamine pyrophosphate (TPP)

Q10. Which type of fermentation is commonly used in yogurt production?

  • Propionic fermentation
  • Homolactic fermentation by Lactobacillus and Streptococcus thermophilus
  • Butanediol fermentation
  • Mixed acid fermentation by Enterobacteriaceae

Correct Answer: Homolactic fermentation by Lactobacillus and Streptococcus thermophilus

Q11. Which intermediate is directly reduced to form ethanol during yeast fermentation?

  • Acetyl-CoA
  • Acetaldehyde
  • Pyruvate
  • Oxaloacetate

Correct Answer: Acetaldehyde

Q12. Mixed acid fermentation by E. coli produces which major products?

  • Acetone and isopropanol
  • Lactate only
  • Lactate, acetate, succinate, ethanol, CO2, and H2
  • Butyric acid and acetoacetate only

Correct Answer: Lactate, acetate, succinate, ethanol, CO2, and H2

Q13. Which test differentiates mixed acid fermenters from butanediol fermenters?

  • Catalase test
  • Methyl red and Voges-Proskauer tests
  • Oxidase test
  • Indole test

Correct Answer: Methyl red and Voges-Proskauer tests

Q14. In lactic acid fermentation in muscle, what causes the accumulation of lactate during intense exercise?

  • Excess oxygen supply
  • Increased pyruvate and NADH due to high glycolytic flux and limited oxidative phosphorylation
  • Inhibition of glycolysis
  • Complete oxidation of glucose in mitochondria

Correct Answer: Increased pyruvate and NADH due to high glycolytic flux and limited oxidative phosphorylation

Q15. Which organism is known for propionic acid fermentation used in cheese ripening?

  • Propionibacterium
  • Clostridium botulinum
  • Lactococcus lactis
  • Saccharomyces cerevisiae

Correct Answer: Propionibacterium

Q16. Which fermentation product is a precursor for nylon and biodegradable polymers in industrial biotechnology?

  • Ethanol
  • Lactic acid
  • Acetone
  • Hydrogen sulfide

Correct Answer: Lactic acid

Q17. During anaerobic fermentation, how is ATP generated?

  • Substrate-level phosphorylation in glycolysis and fermentation steps
  • Oxidative phosphorylation via oxygen
  • ATP synthase using nitrate gradient
  • Photophosphorylation only

Correct Answer: Substrate-level phosphorylation in glycolysis and fermentation steps

Q18. Which enzyme converts acetaldehyde to ethanol in yeast, regenerating NAD+?

  • Alcohol dehydrogenase
  • Aldehyde oxidase
  • Acetyl-CoA synthetase
  • Formate dehydrogenase

Correct Answer: Alcohol dehydrogenase

Q19. What is the net NADH change after glycolysis and homolactic fermentation per glucose?

  • Net gain of 2 NADH
  • No net change in NADH (NADH produced in glycolysis is reoxidized by lactate formation)
  • Net loss of 2 NADH
  • Net gain of 4 NADH

Correct Answer: No net change in NADH (NADH produced in glycolysis is reoxidized by lactate formation)

Q20. Butyric acid fermentation is commonly associated with which genus?

  • Clostridium
  • Streptococcus
  • Bifidobacterium
  • Lactobacillus

Correct Answer: Clostridium

Q21. Which cofactor is reduced to NADH during glycolysis and must be reoxidized during fermentation?

  • FADH2
  • NAD+
  • Biotin
  • Coenzyme A

Correct Answer: NAD+

Q22. In industrial ethanol fermentation, which factor most strongly affects ethanol yield?

  • pH, temperature, yeast strain, and substrate concentration
  • Atmospheric oxygen concentration only
  • Presence of light
  • Amount of inorganic phosphate only

Correct Answer: pH, temperature, yeast strain, and substrate concentration

Q23. Which product formation helps bacteria maintain intracellular pH during fermentation?

  • CO2 and volatile acids (acid production can lower pH; some pathways consume protons or produce neutral products)
  • Only ethanol production raises pH always
  • O2 production
  • ATP hydrolysis only

Correct Answer: CO2 and volatile acids (acid production can lower pH; some pathways consume protons or produce neutral products)

Q24. Which fermentation pathway yields 2,3-butanediol as a major product?

  • Mixed acid fermentation
  • Butanediol fermentation (via acetoin intermediate)
  • Propionic fermentation
  • Homoacetic fermentation

Correct Answer: Butanediol fermentation (via acetoin intermediate)

Q25. Which molecule acts as an electron sink in many fermentations allowing redox balance?

  • ATP
  • Pyruvate derivatives (e.g., acetaldehyde, oxaloacetate)
  • Oxygen
  • Glucose-6-phosphate

Correct Answer: Pyruvate derivatives (e.g., acetaldehyde, oxaloacetate)

Q26. What is the role of formate hydrogenlyase in mixed fermentation?

  • Converts formate to CO2 and H2, influencing redox balance
  • Oxidizes ethanol to acetaldehyde
  • Synthesizes ATP via proton pumping
  • Reduces nitrate to nitrite

Correct Answer: Converts formate to CO2 and H2, influencing redox balance

Q27. Which bacterial fermentation produces acetone and butanol industrially?

  • Clostridial ABE fermentation (Acetone-Butanol-Ethanol)
  • Propionic fermentation
  • Homolactic fermentation
  • Butanediol fermentation

Correct Answer: Clostridial ABE fermentation (Acetone-Butanol-Ethanol)

Q28. Which condition favors fermentation over respiration in facultative anaerobes?

  • High oxygen availability
  • Low oxygen or absence of terminal electron acceptors and high glycolytic substrate flux
  • Excess nitrate as electron acceptor
  • High ATP/ADP ratio

Correct Answer: Low oxygen or absence of terminal electron acceptors and high glycolytic substrate flux

Q29. Why is ATP yield lower in fermentation compared to aerobic respiration?

  • Fermentation uses oxidative phosphorylation more efficiently
  • Fermentation relies mainly on substrate-level phosphorylation and lacks a high-efficiency electron transport chain using O2 as terminal acceptor
  • Fermentation produces more NADH for oxidative phosphorylation
  • Fermentation completely oxidizes substrates to CO2

Correct Answer: Fermentation relies mainly on substrate-level phosphorylation and lacks a high-efficiency electron transport chain using O2 as terminal acceptor

Q30. In pharmaceutical fermentation processes, sterility is critical because:

  • Contaminants can alter product yield, produce toxins, or consume substrate
  • Sterility increases the rate of glycolysis
  • Non-sterile conditions favor higher ethanol production always
  • Sterility is only aesthetic and not functionally important

Correct Answer: Contaminants can alter product yield, produce toxins, or consume substrate

Q31. Which metabolite accumulates in pyruvate kinase deficiency affecting fermentation in erythrocytes?

  • Excess ATP
  • Increased 2,3-bisphosphoglycerate and decreased ATP, leading to hemolytic anemia; fermentation (glycolysis) compromised
  • Increased oxidative phosphorylation
  • Excess glycogen synthesis only

Correct Answer: Increased 2,3-bisphosphoglycerate and decreased ATP, leading to hemolytic anemia; fermentation (glycolysis) compromised

Q32. Which analytical method is commonly used to monitor fermentation product concentrations in process control?

  • Gas chromatography, HPLC, and spectrophotometry
  • Light microscopy only
  • Gel electrophoresis only
  • Mass spectrometry never used

Correct Answer: Gas chromatography, HPLC, and spectrophotometry

Q33. Which fermentation increases NADPH rather than NADH to support biosynthetic reactions?

  • Homofermentation producing only lactate
  • Pentose phosphate pathway activity provides NADPH; not classical fermentation
  • Alcoholic fermentation by yeast produces NADPH
  • Mixed acid fermentation produces NADPH directly

Correct Answer: Pentose phosphate pathway activity provides NADPH; not classical fermentation

Q34. Which product of fermentation is responsible for the sour taste in fermented dairy products?

  • Ethanol
  • Lactic acid
  • Acetone
  • Hydrogen gas

Correct Answer: Lactic acid

Q35. How does oxygen presence affect NADH reoxidation strategies in facultative anaerobes?

  • Oxygen prevents NADH oxidation
  • In presence of oxygen, NADH is preferentially oxidized via the electron transport chain yielding more ATP; under anaerobic conditions fermentation pathways reoxidize NADH
  • Oxygen always converts fermentation to photosynthesis
  • Oxygen only affects lipid metabolism

Correct Answer: In presence of oxygen, NADH is preferentially oxidized via the electron transport chain yielding more ATP; under anaerobic conditions fermentation pathways reoxidize NADH

Q36. Which intermediate diverts to ethanol production in yeast after pyruvate decarboxylation?

  • Formate
  • Acetaldehyde
  • Acetyl-CoA directly becomes ethanol
  • Succinate

Correct Answer: Acetaldehyde

Q37. Which enzyme deficiency would impair homolactic fermentation in mammals?

  • Hexokinase deficiency only
  • Lactate dehydrogenase deficiency
  • Glucose-6-phosphatase deficiency
  • ATP synthase deficiency only

Correct Answer: Lactate dehydrogenase deficiency

Q38. In heterofermentative lactic acid bacteria, what pathway converts pentoses to lactate and ethanol?

  • Embden-Meyerhof (glycolytic) pathway only
  • Phosphoketolase pathway
  • Citric acid cycle exclusively
  • β-oxidation pathway

Correct Answer: Phosphoketolase pathway

Q39. Which fermentation product is linked to “bloat” in ruminants due to rapid starch fermentation?

  • Ethanol causing intoxication
  • Excessive lactic acid leading to acidosis and gas production
  • Propionate reducing gas
  • Carbon dioxide only with no acids

Correct Answer: Excessive lactic acid leading to acidosis and gas production

Q40. Which pathway allows some bacteria to generate a proton motive force anaerobically using nitrate reduction?

  • Fermentation only, without electron transport
  • Anaerobic respiration via nitrate reductase and electron transport chain
  • Strict glycolysis with no membrane components
  • Photosynthetic electron transport only

Correct Answer: Anaerobic respiration via nitrate reductase and electron transport chain

Q41. In industrial antibiotic production, secondary metabolite formation is often linked to which metabolic state?

  • Log-phase exponential growth with maximum primary metabolism
  • Stationary phase and nutrient limitation that redirect metabolism toward secondary metabolites including fermentation-related processes
  • Strictly aerobic high-oxygen conditions only
  • Complete absence of glycolysis

Correct Answer: Stationary phase and nutrient limitation that redirect metabolism toward secondary metabolites including fermentation-related processes

Q42. Which compound is a common fermentation inhibitor produced at high sugar concentrations and low pH that affects yeast?

  • Glycerol only
  • Ethanol accumulation
  • Nitrite formation
  • Oxygen radicals only

Correct Answer: Ethanol accumulation

Q43. Which fermentation is used in production of Swiss-type cheeses and produces CO2 to form eyes?

  • Homofermentation by Lactococcus
  • Propionic acid fermentation by Propionibacterium producing propionate, acetate, and CO2
  • Alcoholic fermentation by yeast only
  • Butyric fermentation producing no gas

Correct Answer: Propionic acid fermentation by Propionibacterium producing propionate, acetate, and CO2

Q44. During fermentation, which pathway provides reducing equivalents and precursors for biosynthesis in rapidly dividing microbes?

  • Only oxidative phosphorylation
  • Glycolysis and associated branch pathways (e.g., pentose phosphate) for NADPH and biosynthetic precursors
  • Only the citric acid cycle functioning aerobically
  • β-oxidation exclusively

Correct Answer: Glycolysis and associated branch pathways (e.g., pentose phosphate) for NADPH and biosynthetic precursors

Q45. What is the primary reason certain pathogens use fermentation during infection sites?

  • Infection sites are always oxygen-rich
  • Tissue hypoxia and limited oxygen availability force pathogens to rely on fermentative metabolism to survive and produce virulence factors
  • Fermentation provides more ATP than respiration in vivo
  • Fermentation detoxifies host immune molecules directly

Correct Answer: Tissue hypoxia and limited oxygen availability force pathogens to rely on fermentative metabolism to survive and produce virulence factors

Q46. Which metabolic reaction in fermentation directly consumes NADH?

  • Conversion of pyruvate to acetyl-CoA via pyruvate dehydrogenase
  • Reduction of pyruvate to lactate by lactate dehydrogenase
  • Phosphorylation of ADP to ATP by substrate-level phosphorylation
  • Oxidation of NAD+ to NADH

Correct Answer: Reduction of pyruvate to lactate by lactate dehydrogenase

Q47. Which industrial parameter is adjusted to favor production of lactic acid over ethanol in microbial fermentations?

  • Lowering temperature below microbial growth limits
  • Selecting homofermentative lactic acid bacteria and controlling pH, aeration, and substrate to favor lactate formation
  • Increasing oxygen to promote aerobic respiration
  • Adding nitrate as electron acceptor

Correct Answer: Selecting homofermentative lactic acid bacteria and controlling pH, aeration, and substrate to favor lactate formation

Q48. Which vitamin deficiency would impair pyruvate decarboxylation and certain fermentative steps due to lack of TPP?

  • Vitamin C deficiency
  • Thiamine (vitamin B1) deficiency
  • Vitamin D deficiency
  • Vitamin K deficiency

Correct Answer: Thiamine (vitamin B1) deficiency

Q49. Which gas is commonly produced alongside organic acids during anaerobic fermentation and must be managed in bioreactors?

  • Nitrogen only
  • Hydrogen and carbon dioxide
  • Oxygen only
  • Chlorine gas

Correct Answer: Hydrogen and carbon dioxide

Q50. Which statement best summarizes the pharmaceutical relevance of mastering fermentation biochemistry for B.Pharm students?

  • Understanding fermentation is irrelevant to drug production
  • Knowledge of fermentation informs drug impurity formation only
  • Mastering fermentation biochemistry is essential for antibiotic and biologic production, optimizing yields, controlling contaminants, and linking metabolism to drug action and toxicity
  • Fermentation knowledge only helps in clinical diagnosis and not in manufacturing

Correct Answer: Mastering fermentation biochemistry is essential for antibiotic and biologic production, optimizing yields, controlling contaminants, and linking metabolism to drug action and toxicity

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