Cryopreservation of cells MCQs With Answer

Cryopreservation of cells MCQs With Answer

Introduction: Cryopreservation is a cornerstone technique in modern biopharmaceutical sciences, enabling long‑term storage of cells, tissues, and biological materials with maintained viability and function. For M.Pharm students, understanding cryobiology principles, cryoprotectant selection, cooling and thawing kinetics, and cryobanking practices is essential for drug development, cell therapy, and quality control. This quiz set focuses on mechanistic aspects (ice formation, osmotic stress, vitrification), practical considerations (DMSO toxicity, controlled‑rate freezing, storage conditions), and application‑specific protocols (stem cells, RBCs, gametes). The questions are designed to deepen conceptual knowledge and prepare students for research and regulatory tasks involving cryopreserved biological materials.

Q1. Which cryoprotectant is commonly used as a penetrating agent that reduces intracellular ice formation by equilibrating across cell membranes?

• Trehalose
• Polyvinylpyrrolidone (PVP)
• Dimethyl sulfoxide (DMSO)
• Sodium chloride

Correct Answer: Dimethyl sulfoxide (DMSO)

Q2. What is the main protective mechanism of non‑permeating cryoprotectants such as sucrose or trehalose during freezing?

• Entering the cell to stabilize proteins directly
• Increasing intracellular ice nucleation
• Exerting an osmotic effect to dehydrate cells and stabilize membranes
• Lowering liquid nitrogen vapor pressure

Correct Answer: Exerting an osmotic effect to dehydrate cells and stabilize membranes

Q3. Controlled‑rate freezing is used primarily to:

• Maximize formation of intracellular ice
• Allow gradual cellular dehydration and minimize osmotic shock
• Rapidly vitrify samples without cryoprotectant
• Prevent cryoprotectant penetration into cells

Correct Answer: Allow gradual cellular dehydration and minimize osmotic shock

Q4. Vitrification differs from slow freezing mainly because it:

• Produces large extracellular ice crystals to protect cells
• Transforms the solution into an amorphous glass without ice crystallization
• Requires no cryoprotectants
• Is performed at room temperature

Correct Answer: Transforms the solution into an amorphous glass without ice crystallization

Q5. Which factor increases the risk of cryoinjury during thawing of frozen cells?

• Rapid warming through the glass transition
• Use of buffered cryopreservation media
• Slow warming that permits ice recrystallization
• Pre‑equilibration with penetrating cryoprotectant

Correct Answer: Slow warming that permits ice recrystallization

Q6. Which storage temperature is typically used for long‑term cryobanking of human hematopoietic stem cells?

• −20°C
• −80°C without liquid nitrogen
• −196°C in liquid nitrogen
• 4°C in refrigeration

Correct Answer: −196°C in liquid nitrogen

Q7. Which of the following is a major toxic effect associated with DMSO used as a cryoprotectant?

• Permanent crosslinking of DNA
• Hemolysis and cellular membrane perturbation at high concentration
• Complete prevention of CPA permeation
• Formation of large extracellular crystals

Correct Answer: Hemolysis and cellular membrane perturbation at high concentration

Q8. Ice seeding (induced nucleation) during controlled freezing is performed to:

• Promote intracellular ice formation for better preservation
• Control the temperature at which extracellular ice forms to reduce supercooling
• Increase CPA toxicity intentionally
• Facilitate vitrification at higher temperatures

Correct Answer: Control the temperature at which extracellular ice forms to reduce supercooling

Q9. During cryopreservation, osmotic shock primarily results from:

• Rapid changes in extracellular osmolality when adding or removing cryoprotectants or during freezing/thawing
• Long exposure to liquid nitrogen gas
• Excessive glucose in culture medium
• Insufficient atmospheric pressure in storage tanks

Correct Answer: Rapid changes in extracellular osmolality when adding or removing cryoprotectants or during freezing/thawing

Q10. For cryopreservation of mammalian oocytes and embryos, which permeating cryoprotectant is frequently preferred due to lower toxicity and rapid permeation?

• Glycerol
• Propylene glycol
• Ethylene glycol
• Sorbitol

Correct Answer: Ethylene glycol

Q11. What is “devitrification” in the context of cryopreservation?

• The initial formation of a glassy state during rapid cooling
• The spontaneous crystallization of a previously vitrified sample during warming or storage
• The permanent chemical modification of a cryoprotectant
• The process of equilibrating CPA across the cell membrane

Correct Answer: The spontaneous crystallization of a previously vitrified sample during warming or storage

Q12. Which parameter is most critical to optimize to minimize intracellular ice formation in small, highly permeable cells?

• CPA molecular weight only
• Cooling rate
• Amount of extracellular protein
• Ambient laboratory humidity

Correct Answer: Cooling rate

Q13. Why is rapid removal of DMSO after thawing recommended for many cell types?

• DMSO must remain indefinitely to maintain cell structure
• DMSO is toxic at physiological temperature and prolonged exposure reduces viability
• DMSO converts into glycerol at 37°C
• DMSO prevents cell attachment if retained

Correct Answer: DMSO is toxic at physiological temperature and prolonged exposure reduces viability

Q14. Which monitoring practice helps reduce the risk of cross‑contamination in liquid nitrogen cryobanks?

• Storing samples only in liquid phase rather than vapor phase
• Using sealed, vapor‑phase storage and validated sterile vials or straws
• Pooling multiple donors in a single container to save space
• Regularly adding tap water to storage Dewars

Correct Answer: Using sealed, vapor‑phase storage and validated sterile vials or straws

Q15. Cryoprotectant concentration and exposure time must be balanced because:

• Higher concentration always improves viability regardless of exposure time
• Long exposure at high CPA concentration increases toxicity, while insufficient exposure reduces intracellular protection
• CPAs are inert and have no effect on cells
• Exposure time affects only extracellular ice size

Correct Answer: Long exposure at high CPA concentration increases toxicity, while insufficient exposure reduces intracellular protection

Q16. What is the primary reason red blood cells (RBCs) are typically cryopreserved with glycerol rather than DMSO?

• Glycerol is less viscous than DMSO
• Glycerol permeability and post‑thaw removal protocols for RBCs are well established and less toxic clinically
• RBCs actively metabolize DMSO
• Glycerol prevents bacterial growth better than DMSO

Correct Answer: Glycerol permeability and post‑thaw removal protocols for RBCs are well established and less toxic clinically

Q17. Which assay is commonly used to assess cell membrane integrity immediately after thawing?

• Colony forming unit assay after 2 weeks
• Trypan blue exclusion or propidium iodide staining
• PCR for metabolic genes
• Electron microscopy of intracellular organelles

Correct Answer: Trypan blue exclusion or propidium iodide staining

Q18. In cryopreservation, the term “critical cooling rate” refers to:

• The speed of cooling above which glass formation is impossible
• The cooling rate that ensures an optimal balance between dehydration and intracellular ice avoidance for a given cell and CPA
• The slowest rate at which a freezer can operate
• The rate at which CPA diffuses into extracellular matrix

Correct Answer: The cooling rate that ensures an optimal balance between dehydration and intracellular ice avoidance for a given cell and CPA

Q19. Which strategy reduces ice recrystallization during warming of frozen biological samples?

• Warming very slowly through the melting range
• Using small sample volumes and rapid warming to minimize time in recrystallization temperature range
• Omitting cryoprotectant entirely
• Increasing storage temperature to −80°C prior to thawing

Correct Answer: Using small sample volumes and rapid warming to minimize time in recrystallization temperature range

Q20. For clinical applications, documentation of cryopreservation processes must include which of the following to satisfy regulatory and traceability requirements?

• Only the name of the investigator
• Details of cell source, CPA composition and concentration, cooling and warming rates, storage location, and chain of custody
• Only the type of cryoprotectant used
• Only the brand of liquid nitrogen storage tank

Correct Answer: Details of cell source, CPA composition and concentration, cooling and warming rates, storage location, and chain of custody

Download