Preservation methods for pure cultures MCQs With Answer

Preservation methods for pure cultures MCQs With Answer – This concise, SEO-friendly introduction helps B. Pharm students master culture preservation essentials. Learn key preservation methods for pure cultures including cryopreservation, lyophilization, deep freezing, glycerol stocks, mineral oil overlay, agar slants, and sterile storage techniques. Emphasis on viability, genetic stability, contamination control, cryoprotectants (glycerol, DMSO), storage temperatures (-20°C, -80°C, liquid nitrogen), and revival procedures prepares you for practical lab work and exams. This guide reinforces best practices, quality control, and troubleshooting for long-term maintenance of bacteria, fungi and cell lines. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which preservation method is best known for long-term storage of bacterial cultures at ultra-low temperatures?

• Refrigeration at 4°C
• Storage in mineral oil
• Deep freezing in liquid nitrogen
• Periodic subculturing on agar slants

Correct Answer: Deep freezing in liquid nitrogen

Q2. Which cryoprotectant is most commonly used for preserving microbial cultures in glycerol stocks?

• Dimethyl sulfoxide (DMSO)
• Polyethylene glycol (PEG)
• Glycerol
• Sucrose

Correct Answer: Glycerol

Q3. Lyophilization (freeze-drying) primarily removes which component to preserve cultures?

• Proteins
• Water
• Lipids
• Nucleic acids

Correct Answer: Water

Q4. Which preservation method is most suitable for maintaining plasmid stability in bacterial stocks?

• Periodic subculturing every 2 days
• Storage as lyophilized ampoules
• Deep freezing with suitable cryoprotectant
• Storage under mineral oil at room temperature

Correct Answer: Deep freezing with suitable cryoprotectant

Q5. What is the primary disadvantage of frequent subculturing for culture preservation?

• Risk of contamination and genetic drift
• Lower costs compared to freezing
• Improved viability over time
• Requires liquid nitrogen storage

Correct Answer: Risk of contamination and genetic drift

Q6. Mineral oil overlay on agar slants is mainly used to:

• Promote rapid growth
• Prevent dehydration and reduce metabolic activity
• Lyse cells for DNA extraction
• Increase oxygen availability

Correct Answer: Prevent dehydration and reduce metabolic activity

Q7. Which temperature range is typical for storing glycerol stocks of bacteria for long-term preservation?

• Room temperature (20–25°C)
• Refrigeration (4°C)
• Freezing at -20°C
• Ultra-low temperatures (-80°C or liquid nitrogen)

Correct Answer: Ultra-low temperatures (-80°C or liquid nitrogen)

Q8. Which organism type forms resistant spores that are advantageous for long-term preservation?

• Non-sporulating Gram-negative bacteria
• Yeasts
• Spore-forming Gram-positive bacteria (e.g., Bacillus)
• Mycoplasma

Correct Answer: Spore-forming Gram-positive bacteria (e.g., Bacillus)

Q9. A major benefit of lyophilization over deep freezing is:

• Requires continuous cold-chain storage
• Preserved samples remain dry and are easier to ship
• Higher cost and complexity
• Lower long-term stability

Correct Answer: Preserved samples remain dry and are easier to ship

Q10. Which cryoprotectant can be toxic to some cells at high concentrations but is effective for many eukaryotic cells?

• Glycerol
• DMSO (dimethyl sulfoxide)
• Sodium chloride
• Formaldehyde

Correct Answer: DMSO (dimethyl sulfoxide)

Q11. For preservation of anaerobic bacteria, which additional consideration is crucial?

• High oxygen exposure during storage
• Use of oxygen-free storage environments or anaerobic containers
• Storing at room temperature
• Frequent shaking to aerate

Correct Answer: Use of oxygen-free storage environments or anaerobic containers

Q12. Which preservation method requires sealing cultures in glass ampoules after filling with medium?

• Liquid nitrogen freezing
• Lyophilization and ampoule sealing
• Mineral oil overlay
• Agar slant storage

Correct Answer: Lyophilization and ampoule sealing

Q13. What is an important quality control parameter to monitor for preserved cultures?

• Color of the storage container only
• Viability and genetic stability over time
• Electrical conductivity of the freezer
• Frequency of subculturing regardless of stability

Correct Answer: Viability and genetic stability over time

Q14. Which method is preferred for short-term storage (days to weeks) of pure cultures in the lab?

• Periodic subculturing on agar slants or plates
• Lyophilization
• Deep freezing at -196°C
• Long-term cryobanking

Correct Answer: Periodic subculturing on agar slants or plates

Q15. What role does cryoprotectant concentration play in freezing microbial stocks?

• No impact on survival
• Optimal concentration reduces ice crystal damage and improves survival
• Higher concentration always increases toxicity without benefit
• Only affects thawing speed, not viability

Correct Answer: Optimal concentration reduces ice crystal damage and improves survival

Q16. Which storage temperature is commonly used for medium-term storage of cultures in laboratory freezers?

• 37°C
• 4°C
• -20°C
• -80°C

Correct Answer: -80°C

Q17. Paraffin or sterile liquid paraffin overlays are primarily used to preserve which type of cultures?

• Fastidious aerobic bacteria
• Aerobic yeast cultures
• Microaerophilic or anaerobic cultures on slants
• Frozen cell lines

Correct Answer: Microaerophilic or anaerobic cultures on slants

Q18. What is a key advantage of cryobanking culture collections in reference centers?

• Increased need for subculturing
• Maintains long-term viability and provenance with minimal genetic change
• Requires no documentation
• Eliminates need for quality control

Correct Answer: Maintains long-term viability and provenance with minimal genetic change

Q19. Which preservative approach minimizes metabolic activity but allows revival without freezing?

• Lyophilization
• Storage under mineral oil or paraffin overlay at room temperature
• Storage in liquid nitrogen
• Continuous incubation at 30°C

Correct Answer: Storage under mineral oil or paraffin overlay at room temperature

Q20. Which factor most directly causes damage to cells during freezing?

• Accumulation of nutrients
• Formation of ice crystals and osmotic stress
• High oxygen levels
• UV light exposure

Correct Answer: Formation of ice crystals and osmotic stress

Q21. For preserving fungal spore stocks, the recommended method is often:

• Continuous subculturing on nutrient agar
• Desiccation or storage as dry spore suspensions, or lyophilization
• Keeping cultures at 37°C in broth
• Storing in mineral oil at high humidity

Correct Answer: Desiccation or storage as dry spore suspensions, or lyophilization

Q22. Which storage practice helps prevent cross-contamination in culture repositories?

• Storing multiple strains in one shared tube
• Using clearly labeled, sealed individual vials with records
• Leaving caps loose to allow gas exchange
• Frequent opening of storage racks without sterile technique

Correct Answer: Using clearly labeled, sealed individual vials with records

Q23. What is the typical final glycerol concentration used for bacterial cryopreservation?

• 0.1–0.5%
• 5–20%
• 50–70%
• 100%

Correct Answer: 5–20%

Q24. When reviving frozen cultures, a recommended practice is to:

• Thaw slowly at room temperature for hours
• Thaw quickly in a 37°C water bath and minimize time at intermediate temperatures
• Directly plate frozen cells without thawing
• Refreeze immediately after partial thaw

Correct Answer: Thaw quickly in a 37°C water bath and minimize time at intermediate temperatures

Q25. Which preservation method is least suitable for maintaining eukaryotic cell lines?

• Cryopreservation in liquid nitrogen with DMSO
• Lyophilization
• Controlled-rate freezing and storage in -196°C
• Use of specialized cryobanks and protocols

Correct Answer: Lyophilization

Q26. What is the main purpose of using controlled-rate freezers before transferring vials to liquid nitrogen?

• To slowly warm cultures to room temperature
• To control cooling rate and reduce ice crystal formation for better survival
• To sterilize vials before storage
• To dry samples prior to freezing

Correct Answer: To control cooling rate and reduce ice crystal formation for better survival

Q27. Which of the following is a disadvantage of storing cultures at -20°C instead of -80°C?

• Lower energy consumption
• Higher risk of loss of viability and cellular damage over time
• Improved preservation of genetic traits
• Better long-term stability

Correct Answer: Higher risk of loss of viability and cellular damage over time

Q28. In culture preservation, what does the term ‘viability recovery rate’ refer to?

• Rate at which cultures contaminate neighboring samples
• Percentage of cells that remain alive and culturable after storage and revival
• Speed of growth on selective media
• Amount of cryoprotectant lost during freezing

Correct Answer: Percentage of cells that remain alive and culturable after storage and revival

Q29. Which practice helps maintain genetic fidelity during long-term storage?

• Frequent passage and growth under selective pressure
• Single-cycle preservation methods with minimal subculturing before storage
• Continuous culture at optimal growth temperature
• Exposure to mutagens before storage

Correct Answer: Single-cycle preservation methods with minimal subculturing before storage

Q30. What is an advantage of using glass ampoules for lyophilized cultures?

• They are permeable to moisture
• Provide airtight, sterile long-term storage and ease of transportation
• Require frequent refilling
• Allow easy repeated opening

Correct Answer: Provide airtight, sterile long-term storage and ease of transportation

Q31. For long-term bacterial culture storage, which label information is essential?

• Only the date of storage
• Strain identification, preservation date, cryoprotectant used, and storage conditions
• Name of the lab technician only
• Supplier catalog number only

Correct Answer: Strain identification, preservation date, cryoprotectant used, and storage conditions

Q32. Which of the following is true about freeze-drying proteome and metabolic activity?

• Lyophilization always preserves full metabolic activity
• Lyophilization reduces metabolic activity and stabilizes biomolecules in a dry state
• Lyophilization increases enzymatic reactions
• Lyophilization requires storage at -196°C

Correct Answer: Lyophilization reduces metabolic activity and stabilizes biomolecules in a dry state

Q33. Which approach is commonly used to preserve viral stocks?

• Maintaining at room temperature
• Cryopreservation at -80°C or in liquid nitrogen with stabilizers
• Storage under mineral oil
• Continuous culturing in broth

Correct Answer: Cryopreservation at -80°C or in liquid nitrogen with stabilizers

Q34. What is the role of a cryoprotectant like glycerol in freezing protocols?

• Acts as a nutrient to speed growth
• Protects cells from freeze-induced dehydration and ice damage
• Causes immediate cell lysis
• Raises storage temperature

Correct Answer: Protects cells from freeze-induced dehydration and ice damage

Q35. Which of these is a common indicator of loss of viability after storage?

• Failure to regrow on appropriate culture medium
• Increased colony forming ability
• Enhanced pigment production
• Faster growth rate

Correct Answer: Failure to regrow on appropriate culture medium

Q36. Which preservation method is most compatible with long-term storage of genetically modified strains requiring regulatory documentation?

• Unlabeled slants in a crowded incubator
• Documented cryobanking with secured records and controlled storage
• Keeping duplicates on office bench
• Periodic sharing without records

Correct Answer: Documented cryobanking with secured records and controlled storage

Q37. Which parameter should be minimized to reduce the risk of contamination when retrieving samples from a cryobank?

• Use of sterile tools and minimizing exposure time
• Frequent opening of multiple vials at once
• Leaving storage racks uncovered
• Mixing samples between racks

Correct Answer: Use of sterile tools and minimizing exposure time

Q38. What is the effect of repeated freeze-thaw cycles on microbial stocks?

• Enhances genetic stability
• Reduces viability and may damage cells
• Has no effect
• Always increases growth rate

Correct Answer: Reduces viability and may damage cells

Q39. Which medium additive can stabilize proteins and membrane structures during freezing?

• Sodium hydroxide
• Bovine serum albumin (BSA) or sugars like trehalose
• Chlorine bleach
• Acetic acid

Correct Answer: Bovine serum albumin (BSA) or sugars like trehalose

Q40. Which storage practice supports traceability in a culture collection?

• No documentation to save time
• Maintaining detailed records, batch numbers, and storage logs
• Relying on memory of personnel
• Labeling vials with only color codes

Correct Answer: Maintaining detailed records, batch numbers, and storage logs

Q41. Why is controlled humidity important for lyophilized biological samples?

• High humidity improves powder stability
• Low humidity prevents moisture uptake and preserves stability
• Humidity has no impact on lyophilized products
• Lyophilized samples must be kept wet

Correct Answer: Low humidity prevents moisture uptake and preserves stability

Q42. Which preservation strategy is often used for short-term stock exchange between labs?

• Shipping live cultures in growth phase without protection
• Sending lyophilized ampoules or frozen dry ice shipments
• Mailing open vials
• Transporting as agar plates at room temperature

Correct Answer: Sending lyophilized ampoules or frozen dry ice shipments

Q43. For preserving cultures of extremophiles, what special consideration is often required?

• Use standard lab temperatures and media only
• Maintain their native conditions (salinity, pH, temperature) during preservation and revival
• Always use glycerol regardless of organism
• Ignore native conditions during freezing

Correct Answer: Maintain their native conditions (salinity, pH, temperature) during preservation and revival

Q44. Which of the following best describes a seed lot system in culture preservation?

• Continuous culture without backups
• Hierarchical system of primary, working, and production stocks to limit passages
• Random sampling of cultures
• Storage at room temperature only

Correct Answer: Hierarchical system of primary, working, and production stocks to limit passages

Q45. What is the typical purpose of including a stabilizer such as skim milk in freeze-drying medium?

• To promote contamination
• To protect cellular structures during drying and storage
• To decrease shelf life
• To make samples heavier

Correct Answer: To protect cellular structures during drying and storage

Q46. Which documentation is essential when depositing strains in a public culture collection?

• Only the depositor’s phone number
• Strain description, origin, growth conditions, and preservation method
• Only the preferred storage temperature
• No documentation required

Correct Answer: Strain description, origin, growth conditions, and preservation method

Q47. Which factor does NOT contribute to cell damage during cryopreservation?

• Osmotic shock during freezing and thawing
• Ice crystal formation
• Use of optimal cryoprotectant concentration
• Thermal fluctuation causing recrystallization

Correct Answer: Use of optimal cryoprotectant concentration

Q48. When storing bacterial cultures under mineral oil, which type of metabolism is primarily reduced?

• Anaerobic respiration
• Metabolic activity due to oxygen exclusion and limited diffusion
• Photosynthesis
• Thermophilic enzyme activity only

Correct Answer: Metabolic activity due to oxygen exclusion and limited diffusion

Q49. Which procedural step is important immediately after thawing a frozen microbial vial?

• Refreeze immediately without recovery
• Dilute and inoculate into fresh medium promptly to recover cells
• Leave at room temperature for 24 hours without adding nutrients
• Expose to high shear mixing

Correct Answer: Dilute and inoculate into fresh medium promptly to recover cells

Q50. Which biosafety consideration is critical when maintaining culture preservation facilities?

• Ignoring containment for low-risk organisms
• Appropriate containment level, PPE, training, and decontamination procedures
• Allowing unrestricted access to storage areas
• Storing pathogenic and non-pathogenic strains together without labeling

Correct Answer: Appropriate containment level, PPE, training, and decontamination procedures

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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