Media for fermentation MCQs With Answer

Introduction: This quiz series on Media for Fermentation is designed specifically for M.Pharm students studying Bioprocess Engineering and Technology. It focuses on the composition, function and practical selection of media used in microbial and cell fermentations. Questions cover defined vs complex media, carbon and nitrogen sources, trace elements, buffers, sterilization methods, selective and differential media, osmotic and pH control, antifoams, gelling agents and media optimization principles relevant to pharmaceutical fermentations. The set balances conceptual understanding with applied knowledge needed for designing, preparing and troubleshooting fermentation media in lab and industrial settings, helping students prepare for exams and practical work.

Q1. What is the primary role of the carbon source in fermentation media?

• Provide osmotic balance for cells
• Serve as energy source and carbon skeleton for biosynthesis
• Act as a sterilizing agent
• Function as a gelling agent in solid media

Correct Answer: Serve as energy source and carbon skeleton for biosynthesis

Q2. Which statement best distinguishes a defined (synthetic) medium from a complex medium?

• Defined media contain peptones and yeast extract while complex media use pure chemicals
• Defined media have all components known chemically and in exact amounts; complex media contain undefined extracts
• Complex media are always sterile filtered; defined media are always autoclaved
• Complex media never support rapid growth whereas defined media always do

Correct Answer: Defined media have all components known chemically and in exact amounts; complex media contain undefined extracts

Q3. Which medium is a classical defined minimal medium commonly used for Escherichia coli?

• LB (Luria–Bertani) broth
• M9 minimal medium
• YPD medium
• SDB (Sabouraud Dextrose Broth)

Correct Answer: M9 minimal medium

Q4. Which of the following is a common rich (complex) medium used for general bacterial cultivation?

• M9 medium
• LB (Luria–Bertani) broth
• Mineral salts medium
• Defined synthetic medium I

Correct Answer: LB (Luria–Bertani) broth

Q5. What is the main purpose of phosphate salts (e.g., KH2PO4 / K2HPO4) in many fermentation media?

• Act as antifoam agents
• Provide buffering capacity and a source of phosphorus
• Serve as primary carbon sources
• Function as solidifying agents

Correct Answer: Provide buffering capacity and a source of phosphorus

Q6. Which gelling agent is thermostable and widely used for preparation of solid microbiological media?

• Gelatin
• Agar
• Polyethylene glycol
• Cellulose

Correct Answer: Agar

Q7. Typical standard autoclave conditions for sterilizing most fermentation media are:

• 100°C for 60 minutes at atmospheric pressure
• 121°C at 15 psi for 15–20 minutes
• 80°C for 30 minutes with continuous agitation
• Dry heat 160°C for 2 hours

Correct Answer: 121°C at 15 psi for 15–20 minutes

Q8. Which pore size filter is typically used for sterile filtration of heat-labile media components and solutions?

• 5.0 µm
• 0.45 µm
• 0.22 µm
• 10 µm

Correct Answer: 0.22 µm

Q9. Which complex nitrogen source is derived from enzymatic or acid hydrolysis of proteins and commonly used in fermentation media?

• Ammonium sulfate
• Peptone
• Sodium nitrate
• Monosodium glutamate

Correct Answer: Peptone

Q10. Which trace element is most critical for redox enzymes and often added in micromolar amounts in fermentation media?

• Calcium
• Iron
• Potassium
• Sodium

Correct Answer: Iron

Q11. Why are certain vitamins (e.g., biotin, thiamine) added after heat sterilization rather than autoclaving with the medium?

• They increase media viscosity if autoclaved
• They are heat-labile and may degrade during autoclaving
• They react with agar to form precipitates
• They act as antimicrobial agents at high temperature

Correct Answer: They are heat-labile and may degrade during autoclaving

Q12. Mannitol Salt Agar (MSA) functions as a selective medium primarily due to which component?

• Mannitol as the only carbon source
• High sodium chloride concentration (≈7.5%)
• Presence of peptone
• Use of phenol red indicator

Correct Answer: High sodium chloride concentration (≈7.5%)

Q13. What is the effect of high solute concentration (e.g., high sugar) on water activity (aw) and microbial growth?

• Increases water activity and stimulates all microbes
• Decreases water activity causing osmotic stress and inhibiting many microbes
• Has no effect on water activity
• Always increases biomass yield proportionally

Correct Answer: Decreases water activity causing osmotic stress and inhibiting many microbes

Q14. Which compound is commonly used as a chelating agent in media to sequester divalent cations such as Ca2+ and Mg2+ during analytical or selective procedures?

• EDTA (ethylenediaminetetraacetic acid)
• Sodium chloride
• Glucose
• Peptone

Correct Answer: EDTA (ethylenediaminetetraacetic acid)

Q15. Which of the following describes carbon catabolite repression relevant to fermentation media?

• High salt concentrations repress carbon uptake
• Presence of a preferred carbon source (e.g., glucose) suppresses utilization of alternative substrates
• Carbon sources always act independently and do not influence each other
• Carbon catabolite repression is caused by excess nitrogen

Correct Answer: Presence of a preferred carbon source (e.g., glucose) suppresses utilization of alternative substrates

Q16. For production of many secondary metabolites (antibiotics) in microbes, which media characteristic is most influential?

• Very high initial glucose concentration only
• Optimized carbon to nitrogen (C:N) ratio and limiting growth conditions
• Complete absence of phosphate
• Excessive aeration irrespective of nutrient balance

Correct Answer: Optimized carbon to nitrogen (C:N) ratio and limiting growth conditions

Q17. Which antifoam type is most commonly used in large-scale aerobic fermentations due to chemical inertness and stability?

• Silicone-based antifoams
• Strong acids
• High concentrations of detergents
• Hydrogen peroxide

Correct Answer: Silicone-based antifoams

Q18. When preparing media that contains heat-labile proteins or enzymes, which sterilization method is preferred for those components?

• Autoclaving at 121°C
• Pasteurization at 60°C
• Sterile filtration through a 0.22 µm membrane
• Dry heat at 160°C

Correct Answer: Sterile filtration through a 0.22 µm membrane

Q19. Which medium is typically used for cultivation of yeasts and some fungi and is rich in complex nitrogen and carbon sources?

• M9 minimal salts medium
• YPD (Yeast extract Peptone Dextrose) medium
• Mannitol Salt Agar
• Simulated seawater medium

Correct Answer: YPD (Yeast extract Peptone Dextrose) medium

Q20. Why are trace element solutions added in very low concentrations to fermentation media?

• They act as major carbon sources
• They are toxic at low concentrations and must be minimized
• They serve as essential cofactors for metalloenzymes and must be present at micromolar levels
• They increase the viscosity of the medium

Correct Answer: They serve as essential cofactors for metalloenzymes and must be present at micromolar levels

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