Immobilization of whole cells MCQs With Answer

Introduction: Immobilization of whole cells is a key concept in bioprocess engineering for M.Pharm students, combining microbiology and reactor design to stabilize living cells on or within supports for repeated use. This blog gives a concise but thorough collection of multiple-choice questions focused on mechanisms (adsorption, entrapment, covalent binding, cross-linking), common matrices (alginate, polyacrylamide, chitosan), mass transfer and oxygen limitations, reactor types and scale-up issues, and pharmaceutical safety considerations. These MCQs are crafted to test conceptual understanding, practical choices for formulation and reactors, and interpretation of operational trade-offs important for designing immobilized-cell processes in pharmaceutical biotransformations and continuous production systems.

Q1. Which statement best defines immobilization of whole cells?

• Genetic modification of cells to produce higher yields
• Entrapment or attachment of intact microbial cells within or on a support to restrict their mobility
• Lyophilization of cells for long-term storage
• Separation of cells from broth using centrifugation

Correct Answer: Entrapment or attachment of intact microbial cells within or on a support to restrict their mobility

Q2. Which immobilization technique is based on ionic gelation commonly used for gentle entrapment of whole cells?

• Cross-linking with glutaraldehyde
• Entrapment in calcium alginate beads formed by dropping alginate-cell mixture into CaCl2
• Covalent coupling to epoxy-activated resins
• Adsorption onto hydrophobic beads

Correct Answer: Entrapment in calcium alginate beads formed by dropping alginate-cell mixture into CaCl2

Q3. Which of the following is the primary operational advantage of immobilizing whole cells in a bioprocess?

• Elimination of mass transfer limitations
• Complete prevention of mutation
• Facilitates reuse of biomass and improves operational stability of the biocatalyst
• Guaranteed sterility of the process

Correct Answer: Facilitates reuse of biomass and improves operational stability of the biocatalyst

Q4. What is the most common disadvantage associated with immobilized whole-cell systems?

• Unlimited cell growth within the matrix
• Severe nutrient toxicity
• Mass transfer limitations of substrates and products through the support matrix
• Inability to operate continuously

Correct Answer: Mass transfer limitations of substrates and products through the support matrix

Q5. Which type of carrier is most likely to cause substantial internal diffusion resistance for whole-cell immobilization?

• Non-porous glass beads
• Macroporous ceramic supports
• Hydrogel beads such as alginate with a dense polymer network
• Open-structured fibrous carriers

Correct Answer: Hydrogel beads such as alginate with a dense polymer network

Q6. Glutaraldehyde is commonly used in immobilization to:

• Chelate metal ions and dissolve the carrier
• Act as an ionic gelating agent like CaCl2
• Cross-link proteins and form covalent bonds between cell surface amino groups and carrier functional groups
• Increase pore size of hydrogels

Correct Answer: Cross-link proteins and form covalent bonds between cell surface amino groups and carrier functional groups

Q7. Which immobilization method involves forming a stable covalent bond between cell surface moieties and an activated support?

• Adsorption
• Entrapment
• Covalent binding to activated carriers (e.g., epoxy- or aldehyde-activated supports)
• Physical encapsulation in liposomes

Correct Answer: Covalent binding to activated carriers (e.g., epoxy- or aldehyde-activated supports)

Q8. For aerobic whole-cell immobilized bioprocesses, the most frequent limiting factor inside beads is:

• pH gradient formation only
• Excessive shear stress inside the bead
• Oxygen diffusion into the interior of the immobilized particle
• Overly rapid substrate diffusion causing toxicity

Correct Answer: Oxygen diffusion into the interior of the immobilized particle

Q9. Which pore size range is generally preferred in macroporous carriers to accommodate whole microbial cells and reduce entrapment stress?

• Pore size below 10 nm (nanoporous)
• Pore size 50–200 nm
• Pore size greater than 1 µm (macroporous)
• Pore size exactly 100 µm only

Correct Answer: Pore size greater than 1 µm (macroporous)

Q10. How does decreasing the diameter of immobilized cell beads typically affect mass transfer and reactor performance?

• Smaller beads increase internal diffusion distances and worsen transfer
• Smaller beads decrease surface area-to-volume ratio
• Smaller beads reduce diffusion path length, improving mass transfer and often increasing volumetric productivity
• Bead size has no effect on mass transfer

Correct Answer: Smaller beads reduce diffusion path length, improving mass transfer and often increasing volumetric productivity

Q11. Which coating is commonly applied to calcium alginate beads to reduce cell leakage and improve mechanical strength?

• Poly-L-lysine or chitosan coating
• Direct autoclaving of beads
• Silicone oil impregnation
• Freeze-drying the beads

Correct Answer: Poly-L-lysine or chitosan coating

Q12. Which immobilization approach is generally considered the gentlest and most likely to preserve whole-cell metabolic activity?

• Covalent coupling with strong cross-linkers
• Entrapment/encapsulation in biocompatible hydrogels (e.g., alginate)
• Harsh chemical adsorption onto activated carbon
• Dehydration and chemical fixation

Correct Answer: Entrapment/encapsulation in biocompatible hydrogels (e.g., alginate)

Q13. Which reactor configuration is most suitable for continuous high-cell-density biotransformations with immobilized whole cells and low biomass washout?

• Batch stirred tank reactor only
• Packed-bed reactor loaded with immobilized carriers
• Open pond cultivation
• Shake flask

Correct Answer: Packed-bed reactor loaded with immobilized carriers

Q14. Which performance metric best compares catalytic performance between free and immobilized whole-cell systems in a given reactor volume?

• Number of immobilization steps
• Volumetric productivity (product per unit reactor volume per unit time)
• Color of the carrier
• Cell doubling time only outside the matrix

Correct Answer: Volumetric productivity (product per unit reactor volume per unit time)

Q15. What does co-immobilization mean in the context of whole-cell bioprocesses?

• Immobilizing cells sequentially one after another
• Immobilizing two or more different microbial species or strains together within the same carrier to perform coupled reactions
• Immobilizing only enzymes while keeping cells free
• Using different carriers in alternate reactor zones

Correct Answer: Immobilizing two or more different microbial species or strains together within the same carrier to perform coupled reactions

Q16. Which experimental test is commonly used to quantify operational stability of immobilized whole-cell catalysts?

• Measuring bead color after storage
• Determining activity retention over repeated batch cycles or continuous run time
• Counting the number of beads by weight
• Measuring only initial reaction rate once

Correct Answer: Determining activity retention over repeated batch cycles or continuous run time

Q17. Which statement describes ionic gelation used for whole-cell immobilization?

• Cross-linking proteins using aldehydes
• Formation of a gel by ionic interaction between polyanionic polymers (e.g., alginate) and multivalent cations (e.g., Ca2+)
• Sintering of polymer beads at high temperature
• Embedding cells in a hydrophobic solvent matrix

Correct Answer: Formation of a gel by ionic interaction between polyanionic polymers (e.g., alginate) and multivalent cations (e.g., Ca2+)

Q18. What is a typical effect of extensive covalent cross-linking (e.g., with glutaraldehyde) on whole-cell catalysts?

• Improves cell viability but reduces mechanical stability
• Increases mechanical strength and thermal stability but may reduce cell viability and metabolic activity
• Always increases catalytic turnover number without drawbacks
• Causes immediate dissolution of the carrier

Correct Answer: Increases mechanical strength and thermal stability but may reduce cell viability and metabolic activity

Q19. Which regulatory or safety concern is most relevant when using immobilized pathogenic or Gram-negative whole cells in pharmaceutical bioprocesses?

• Potential for endotoxin contamination and cell leakage leading to product contamination
• Excessive flavor formation
• Ineffective mixing of media components
• Color change of beads

Correct Answer: Potential for endotoxin contamination and cell leakage leading to product contamination

Q20. Which sterilization/aseptic approach is most appropriate for fragile hydrogel-entrapped whole-cell preparations intended for pharmaceutical biotransformations?

• Autoclaving the final hydrogel beads after cell entrapment
• Gamma irradiation of live-cell beads at high dose
• Assembling beads aseptically from sterile components and performing sterile processing rather than autoclaving finished beads
• Soaking beads in concentrated acid to sterilize

Correct Answer: Assembling beads aseptically from sterile components and performing sterile processing rather than autoclaving finished beads

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