Q.1 Which type of impeller is most commonly used for high-viscosity cultures in stirred‑tank bioreactors?
Propeller
Rushton turbine
Helical ribbon
Axial flow impeller
Explanation - Helical ribbon impellers generate axial flow and are better suited for viscous media, providing higher shear while reducing power consumption.
Correct answer is: Helical ribbon
Q.2 What is the primary function of a sparger in a bioreactor’s aeration system?
To mix the culture
To regulate temperature
To deliver air bubbles into the liquid
To monitor pH
Explanation - Spargers disperse gas into fine bubbles, increasing gas‑liquid mass transfer for oxygen supply.
Correct answer is: To deliver air bubbles into the liquid
Q.3 Which parameter is most directly influenced by the agitator speed?
Biomass concentration
Oxygen transfer rate (OTR)
Medium pH
Temperature gradient
Explanation - Agitator speed increases mixing and turbulence, enhancing gas‑liquid contact and thus OTR.
Correct answer is: Oxygen transfer rate (OTR)
Q.4 In a bubble column bioreactor, which of the following is the main drawback of increasing the gas flow rate?
Higher oxygen uptake
Lower power consumption
Reduced mixing efficiency
Increased shear stress
Explanation - Excessive gas flow can lead to poor liquid circulation, resulting in poor mixing and mass transfer.
Correct answer is: Reduced mixing efficiency
Q.5 Which of the following is a key advantage of using a micro‑bubble diffuser?
Simpler construction
Lower power demand
Higher oxygen transfer efficiency
Reduced cost of operation
Explanation - Micro‑bubbles have a larger surface area per volume, increasing the rate of gas transfer to the culture.
Correct answer is: Higher oxygen transfer efficiency
Q.6 What does the dimensionless number 'Reynolds number' indicate in the context of bioreactor impeller design?
Turbulence level
Power consumption
Shear stress distribution
Temperature rise
Explanation - Reynolds number predicts whether flow is laminar or turbulent, which influences mixing and oxygen transfer.
Correct answer is: Turbulence level
Q.7 Which type of motor controller is commonly used to adjust the speed of an agitator in response to a setpoint?
On/Off relay
Pulse‑width modulation (PWM) drive
Step‑per motor controller
Manual throttle
Explanation - PWM drives allow precise, variable speed control of DC or AC motors, essential for optimizing agitation.
Correct answer is: Pulse‑width modulation (PWM) drive
Q.8 During scale‑up, why is it important to maintain the same power input per unit volume (P/V) as in the laboratory scale?
To keep temperature constant
To preserve the same mixing intensity
To reduce oxygen transfer
To increase shear stress
Explanation - Maintaining P/V ensures similar hydrodynamic conditions, preserving product quality across scales.
Correct answer is: To preserve the same mixing intensity
Q.9 What is the primary purpose of a dissolved oxygen probe in a bioreactor?
Measure pH
Measure temperature
Monitor oxygen levels
Detect impurities
Explanation - Dissolved oxygen probes provide real‑time feedback on O₂ availability for cells, enabling control loops.
Correct answer is: Monitor oxygen levels
Q.10 Which of the following statements best describes the effect of increasing the impeller tip speed?
Decreases power consumption
Increases mixing efficiency
Reduces oxygen transfer
Lowens the temperature
Explanation - Higher tip speeds create stronger turbulence, enhancing mixing and mass transfer.
Correct answer is: Increases mixing efficiency
Q.11 Why is a two‑stage mixing strategy often employed in fed‑batch processes?
To reduce oxygen consumption
To minimize temperature fluctuations
To balance mixing with shear sensitivity
To increase power consumption
Explanation - Initial vigorous mixing ensures homogeneity, while gentle mixing later protects shear‑sensitive cells.
Correct answer is: To balance mixing with shear sensitivity
Q.12 Which control strategy can be used to maintain a constant dissolved oxygen setpoint in a bioreactor?
PID control of agitation speed
Manual adjustment of gas flow
Constant temperature setpoint
Fixed feeding rate
Explanation - A PID loop adjusts agitation speed to keep dissolved oxygen at the desired level.
Correct answer is: PID control of agitation speed
Q.13 What is the effect of increasing the aeration rate in a stirred‑tank bioreactor?
Decreases dissolved oxygen
Increases shear stress
Reduces mixing intensity
Enhances gas‑liquid transfer
Explanation - More gas flow improves oxygen solubility and transfer to the cells, but may increase shear.
Correct answer is: Enhances gas‑liquid transfer
Q.14 Which of the following is a typical material used for impeller construction in a bioreactor?
Stainless steel
Aluminum
Copper
Lead
Explanation - Stainless steel is corrosion‑resistant and biocompatible, suitable for mixing media.
Correct answer is: Stainless steel
Q.15 What is the role of the ‘gas holdup’ parameter in bubble column design?
Determines the amount of gas in the liquid phase
Measures the temperature of the gas
Calculates the pressure drop
Specifies the impeller diameter
Explanation - Gas holdup indicates how much gas remains in the liquid, influencing mass transfer efficiency.
Correct answer is: Determines the amount of gas in the liquid phase
Q.16 Which of the following sensors is essential for monitoring agitation speed in a bioreactor?
Load cell
Temperature probe
Pressure sensor
Velocity sensor
Explanation - A load cell measures the torque applied to the motor, from which speed is inferred.
Correct answer is: Load cell
Q.17 What is the main advantage of using a variable‑frequency drive (VFD) on a bioreactor agitator?
Reduces oxygen consumption
Allows precise speed control
Increases power usage
Simplifies piping
Explanation - VFDs enable continuous speed adjustment to optimize mixing and minimize shear.
Correct answer is: Allows precise speed control
Q.18 Which of the following best describes the effect of shear stress on mammalian cells in a bioreactor?
Increases growth rate
Has no effect
Can cause cell damage
Reduces oxygen demand
Explanation - High shear can rupture cell membranes, reducing viability in shear‑sensitive mammalian cultures.
Correct answer is: Can cause cell damage
Q.19 During scale‑up, why is the tip speed often maintained constant rather than power input?
To avoid temperature changes
Because tip speed correlates with mixing patterns
Because power input cannot be measured
To reduce oxygen demand
Explanation - Maintaining tip speed preserves similar flow regimes, aiding scale‑up fidelity.
Correct answer is: Because tip speed correlates with mixing patterns
Q.20 What is the primary function of a liquid circulation pump in a parallel‑flow bioreactor?
Supply nutrients
Increase temperature
Drive gas sparging
Create axial flow
Explanation - The pump generates axial motion to improve mass transfer in parallel‑flow designs.
Correct answer is: Create axial flow
Q.21 Which of the following is a common method to measure power input in a bioreactor?
Thermocouple reading
Torque sensor
pH meter
Humidity sensor
Explanation - Torque sensors capture motor torque, from which power input can be calculated.
Correct answer is: Torque sensor
Q.22 Which aeration method typically results in the lowest shear stress on cells?
Sparging with a fine diffuser
High‑pressure sparging
Mechanical agitation only
No aeration
Explanation - Fine diffusers produce small bubbles, reducing turbulence and shear compared to large bubble spargers.
Correct answer is: Sparging with a fine diffuser
Q.23 What does the term 'oxygen transfer coefficient (kLa)' represent?
Rate of oxygen consumption by cells
Mass transfer coefficient times interfacial area
Total dissolved oxygen in the system
Pressure drop across the sparger
Explanation - kLa quantifies how efficiently oxygen is transferred from gas to liquid.
Correct answer is: Mass transfer coefficient times interfacial area
Q.24 Which of the following factors does NOT affect the kLa in a stirred bioreactor?
Gas flow rate
Impeller speed
Liquid viscosity
Ambient light intensity
Explanation - Light does not influence gas‑liquid mass transfer, unlike flow rate or viscosity.
Correct answer is: Ambient light intensity
Q.25 In a parallel‑flow bioreactor, why is the agitator positioned parallel to the inlet flow?
To reduce power consumption
To improve mixing and reduce boundary layers
To increase temperature uniformity
To simplify control algorithms
Explanation - Parallel orientation enhances axial mixing, minimizing dead zones.
Correct answer is: To improve mixing and reduce boundary layers
Q.26 Which electrical component is most critical for protecting a bioreactor’s agitator motor from overload?
Fuse
Relay
Capacitor
Inductor
Explanation - A fuse limits current to safe levels, preventing motor damage from overload conditions.
Correct answer is: Fuse
Q.27 Which of the following is NOT a typical parameter monitored by a bioprocess control system?
Dissolved oxygen
pH
Ambient humidity
Temperature
Explanation - Bioprocess systems focus on medium parameters, not external humidity.
Correct answer is: Ambient humidity
Q.28 What is the typical range of power density (P/V) for large‑scale bioreactors using Rushton turbines?
0.05–0.1 W/L
0.5–1.0 W/L
5–10 W/L
50–100 W/L
Explanation - Large‑scale stirred tanks often operate between 0.5 and 1.0 W per liter for adequate mixing.
Correct answer is: 0.5–1.0 W/L
Q.29 Which of the following best describes a ‘pulsating’ aeration strategy?
Continuous steady gas flow
Intermittent high‑flow bursts
Gradual increase over time
Zero aeration during initial growth
Explanation - Pulsating aeration involves alternating periods of high and low gas flow to optimize transfer.
Correct answer is: Intermittent high‑flow bursts
Q.30 During bioreactor startup, which sensor provides immediate feedback on potential fouling of the sparger?
Temperature probe
pH probe
Pressure drop sensor
Torque sensor
Explanation - Increased pressure drop indicates blockages or fouling in the sparger.
Correct answer is: Pressure drop sensor
Q.31 Which type of impeller is considered 'low shear' and thus suitable for mammalian cell culture?
Rushton turbine
Beckman impeller
Pitch‑fork impeller
Magnetic stirrer
Explanation - Pitch‑fork impellers generate gentle, planar flow, minimizing cell damage.
Correct answer is: Pitch‑fork impeller
Q.32 What is the main advantage of using a magnetic stirrer in a laboratory‑scale bioreactor?
High power consumption
Easy control of speed
Complex plumbing
High shear environment
Explanation - Magnetic stirrers provide simple, precise speed control with minimal mechanical components.
Correct answer is: Easy control of speed
Q.33 Why is it important to maintain a constant temperature during agitation in a bioreactor?
To preserve cell membrane integrity
Because agitation causes temperature rise
To improve oxygen solubility
All of the above
Explanation - Agitation generates heat, which can affect cell viability and oxygen transfer rates.
Correct answer is: All of the above
Q.34 Which sensor type is commonly used for measuring dissolved oxygen in a bioreactor?
Clark electrode
Thermocouple
pH meter
Conductivity probe
Explanation - The Clark electrode uses a platinum cathode to measure oxygen concentration via current.
Correct answer is: Clark electrode
Q.35 In a parallel‑flow bioreactor, what is the primary benefit of a 'side‑by‑side' sparger configuration?
Uniform gas distribution
Lower power consumption
Simplified maintenance
Higher oxygen transfer rates
Explanation - Side‑by‑side spargers reduce local gas concentration gradients, improving homogeneity.
Correct answer is: Uniform gas distribution
Q.36 Which of the following is a key parameter that influences shear stress in a stirred tank?
Impeller speed
Medium viscosity
Tank volume
Both A and B
Explanation - Shear stress depends on turbulence from impeller speed and resistance from viscosity.
Correct answer is: Both A and B
Q.37 What does the term 'hydrodynamic scaling' refer to in bioreactor design?
Matching power input across scales
Matching Reynolds number across scales
Matching kLa across scales
All of the above
Explanation - Hydrodynamic scaling involves matching key dimensionless numbers and parameters to preserve mixing behavior.
Correct answer is: All of the above
Q.38 Which control strategy is best suited for maintaining a constant dissolved oxygen level under varying cell growth rates?
Open‑loop feedrate
PID control of aeration rate
Manual adjustment of temperature
Fixed agitation speed
Explanation - PID loops adapt aeration to real‑time O₂ demands, compensating for growth variations.
Correct answer is: PID control of aeration rate
Q.39 What is the main reason to use a gas‑liquid mass transfer model during bioreactor design?
To estimate power consumption
To predict oxygen transfer efficiency
To calculate temperature rise
To determine impeller diameter
Explanation - Mass transfer models help quantify kLa and ensure adequate oxygen supply for cell metabolism.
Correct answer is: To predict oxygen transfer efficiency
Q.40 Which of the following is a typical source of electrical noise in a bioreactor control system?
Pumps
Stirred impellers
Temperature sensors
pH probes
Explanation - Pumps generate mechanical vibrations that can couple into the electrical control circuitry.
Correct answer is: Pumps
Q.41 What is the most important safety consideration when designing the aeration system for a large bioreactor?
Avoiding over‑pressure buildup
Minimizing electrical consumption
Ensuring rapid cooling
Maximizing oxygen transfer
Explanation - Pressure spikes can rupture the vessel, so safety reliefs and pressure sensors are critical.
Correct answer is: Avoiding over‑pressure buildup
Q.42 Which of the following best describes the effect of increasing the impeller diameter on power consumption?
Power consumption decreases
Power consumption increases linearly
Power consumption remains constant
Power consumption increases with the cube of diameter
Explanation - Power scales roughly with the cube of impeller diameter for similar tip speeds.
Correct answer is: Power consumption increases with the cube of diameter
Q.43 In a bubble‑column bioreactor, what does the term 'hydrodynamic instability' refer to?
Sudden temperature spikes
Unpredictable gas velocity fluctuations
Variations in pH
Loss of mechanical integrity
Explanation - Instability manifests as irregular bubble behavior, affecting mixing and transfer.
Correct answer is: Unpredictable gas velocity fluctuations
Q.44 Which component in a bioreactor aeration circuit is responsible for controlling the gas composition?
Mass flow controller (MFC)
Pressure relief valve
Temperature sensor
Agitator motor
Explanation - MFCs regulate the flow rate of each gas component, ensuring correct O₂/N₂ ratios.
Correct answer is: Mass flow controller (MFC)
Q.45 What is the typical effect of adding a silicone gasket between the sparger and the bioreactor lid?
Increases power consumption
Reduces gas leakage
Decreases oxygen transfer
Improves temperature control
Explanation - Gaskets seal the sparger opening, preventing gas loss and maintaining pressure.
Correct answer is: Reduces gas leakage
Q.46 Which type of mixer is used when a low‑shear environment is required for delicate microorganisms?
Rushton turbine
Pitch‑fork impeller
Stir bar
Venturi injector
Explanation - Pitch‑fork impellers provide gentle, planar flow suitable for shear‑sensitive cells.
Correct answer is: Pitch‑fork impeller
Q.47 During bioreactor start‑up, why is it important to perform a ‘bubble sweep’ before inoculation?
To remove residual contaminants
To sterilize the culture medium
To increase oxygen levels
All of the above
Explanation - Bubble sweeping flushes the vessel, eliminates airborne microbes, and enriches dissolved oxygen.
Correct answer is: All of the above
Q.48 Which electrical parameter is most directly related to the power draw of an agitator motor?
Voltage
Current
Frequency
Resistance
Explanation - Power = voltage × current; thus current is a direct indicator of power consumption.
Correct answer is: Current
Q.49 What is the primary reason for using a 'mixed‑flow' impeller design?
To generate high turbulence
To create uniform axial and radial flow
To minimize power consumption
To increase shear
Explanation - Mixed‑flow impellers combine axial and radial movement for efficient mixing.
Correct answer is: To create uniform axial and radial flow
Q.50 Which of the following is a key parameter when selecting a sparger material?
Electrical conductivity
Chemical resistance
Color
Weight
Explanation - Spargers contact culture media, so resistance to corrosion is critical.
Correct answer is: Chemical resistance
Q.51 What is the main purpose of a pressure relief valve in a bioreactor system?
To regulate temperature
To maintain constant dissolved oxygen
To protect against over‑pressure
To control agitation speed
Explanation - It opens when pressure exceeds safe limits, preventing vessel rupture.
Correct answer is: To protect against over‑pressure
Q.52 Which control variable is commonly adjusted in a PID loop to keep dissolved oxygen at a setpoint?
pH value
Agitation speed
Temperature
Aeration rate
Explanation - Altering gas flow directly changes dissolved oxygen concentration.
Correct answer is: Aeration rate
Q.53 Why is a ‘dead‑zone’ often present in the mixing pattern of a stirred tank bioreactor?
Due to the geometry of the vessel
Because of impeller design
Both A and B
None of the above
Explanation - The vessel shape and impeller type create regions with poor fluid circulation.
Correct answer is: Both A and B
Q.54 What is the most effective way to reduce the oxygen transfer time in a high‑viscosity culture?
Increase agitator speed
Add a micro‑bubble diffuser
Lower the temperature
Increase the tank volume
Explanation - Micro‑bubbles increase gas–liquid interface, speeding up mass transfer.
Correct answer is: Add a micro‑bubble diffuser
Q.55 Which of the following is an advantage of using a parallel‑flow bioreactor over a stirred‑tank reactor?
Lower shear stresses
Simpler scale‑up
Higher power input
Greater mixing uniformity
Explanation - Parallel flow reduces dead zones, leading to more homogeneous conditions.
Correct answer is: Greater mixing uniformity
Q.56 In a bubble column, which phenomenon limits the oxygen transfer rate at very high gas flow rates?
Bubble coalescence
Increased temperature
Decreased pressure
Reduced impeller speed
Explanation - High flow merges bubbles into larger ones, reducing surface area and O₂ transfer.
Correct answer is: Bubble coalescence
Q.57 What is the most common method to measure the dissolved oxygen level in a bioreactor?
Clark electrode
Thermocouple
pH electrode
Conductivity probe
Explanation - The Clark electrode provides accurate, real‑time O₂ measurements.
Correct answer is: Clark electrode
Q.58 Which of the following factors does NOT influence the oxygen transfer coefficient (kLa) in a bubble column?
Gas flow rate
Bubble size
Medium viscosity
Electrical voltage of the agitator motor
Explanation - kLa is determined by gas and liquid properties, not motor voltage.
Correct answer is: Electrical voltage of the agitator motor
Q.59 Which of the following is a typical response of a bioreactor to a sudden increase in cell density?
Decreased dissolved oxygen
Increased pH
Reduced temperature
Increased agitation speed
Explanation - Higher cell density consumes more oxygen, lowering dissolved levels.
Correct answer is: Decreased dissolved oxygen
Q.60 What is the main reason to use a variable‑frequency drive (VFD) in a bioreactor agitator system?
To reduce motor wear
To control agitation speed precisely
To increase power consumption
To avoid electrical noise
Explanation - VFDs allow fine speed adjustments, optimizing mixing and reducing shear.
Correct answer is: To control agitation speed precisely
Q.61 Which parameter is most directly proportional to the power required for mixing in a stirred tank?
Agitator tip speed
Tank diameter
Liquid density
All of the above
Explanation - Power scales with tip speed, impeller size, and fluid density.
Correct answer is: All of the above
Q.62 What is the effect of increasing the temperature on the dissolved oxygen concentration in the medium?
Increases concentration
Decreases concentration
No effect
Depends on gas flow rate
Explanation - Higher temperatures reduce oxygen solubility in liquids.
Correct answer is: Decreases concentration
Q.63 Which of the following is NOT a typical design criterion for the aeration system in a large‑scale bioreactor?
Pressure drop across the sparger
Sparger geometry
Ambient light intensity
Oxygen transfer efficiency
Explanation - Light levels do not directly affect aeration design.
Correct answer is: Ambient light intensity
Q.64 In a parallel‑flow bioreactor, how does the inlet flow velocity affect mixing?
Higher velocity reduces mixing time
Higher velocity increases dead zones
Velocity has no effect
Lower velocity improves mixing
Explanation - Increased inlet velocity promotes rapid axial mixing and reduces residence time.
Correct answer is: Higher velocity reduces mixing time
Q.65 What is the primary function of a pressure sensor in a bioreactor aeration line?
To monitor temperature
To detect gas flow anomalies
To measure dissolved oxygen
To control agitation speed
Explanation - Pressure sensors detect blockages or leaks that alter flow conditions.
Correct answer is: To detect gas flow anomalies
Q.66 Which of the following is a common method to reduce oxygen transfer time in a bubble column?
Increase gas flow rate
Use a larger sparger pore size
Reduce bubble size
Lower the liquid temperature
Explanation - Smaller bubbles provide larger surface area for transfer, speeding up O₂ uptake.
Correct answer is: Reduce bubble size
Q.67 What is the main advantage of using a Rushton turbine in large bioreactors?
High axial flow
Low power consumption
Uniform mixing
Reduced shear
Explanation - Rushton turbines create radial flow that distributes contents evenly.
Correct answer is: Uniform mixing
Q.68 Which of the following sensors is used to monitor the temperature inside a bioreactor?
pH probe
Temperature probe
Dissolved oxygen probe
Conductivity probe
Explanation - Temperature probes provide real‑time data for process control.
Correct answer is: Temperature probe
Q.69 Which electrical component helps protect a bioreactor motor from voltage surges?
Fuse
Motor controller
Capacitor
Resistor
Explanation - Capacitors smooth voltage spikes, safeguarding motor components.
Correct answer is: Capacitor
Q.70 What is the primary benefit of using a magnetic stirrer for small‑scale bioreactor operations?
High shear stress
Precise speed control
Complex plumbing
High power consumption
Explanation - Magnetic stirrers offer simple, accurate speed adjustment for lab‑scale cultures.
Correct answer is: Precise speed control
Q.71 Which of the following best explains the role of a sparger in a bioreactor?
To maintain temperature
To provide mixing
To deliver gas into the liquid
To measure pH
Explanation - A sparger introduces gas as fine bubbles for oxygen transfer.
Correct answer is: To deliver gas into the liquid
Q.72 Which of the following is a common cause of fouling in a sparger system?
High temperature
Protein deposition
Low pressure
High agitation speed
Explanation - Proteins in the culture can accumulate on sparger surfaces, reducing gas transfer.
Correct answer is: Protein deposition
Q.73 What is the main reason for controlling agitation speed during scale‑up?
To maintain temperature
To ensure uniform mixing
To reduce power consumption
To increase oxygen transfer
Explanation - Consistent speed preserves hydrodynamic conditions across scales.
Correct answer is: To ensure uniform mixing
Q.74 Which of the following is a key design consideration for the aeration line in a bioreactor?
Sparger placement
Electrical grounding
Gas composition
All of the above
Explanation - Placement, electrical safety, and gas mix all affect aeration performance.
Correct answer is: All of the above
Q.75 In a stirred‑tank bioreactor, what does the term 'power density' (P/V) refer to?
Power per unit volume
Power per impeller
Power per unit temperature
Power per unit flow rate
Explanation - P/V quantifies mixing intensity relative to vessel size.
Correct answer is: Power per unit volume
Q.76 What is the effect of increasing the sparger pore size on gas transfer?
Increases transfer
Decreases transfer
No effect
Depends on impeller speed
Explanation - Larger pores produce larger bubbles, reducing surface area and transfer efficiency.
Correct answer is: Decreases transfer
Q.77 Which control variable is directly linked to the dissolved oxygen concentration in a bioreactor?
Temperature
pH
Aeration rate
Agitation speed
Explanation - Aeration determines the amount of oxygen entering the liquid phase.
Correct answer is: Aeration rate
Q.78 Which of the following is NOT an advantage of using a micro‑bubble diffuser in a bioreactor?
Higher kLa
Lower shear stress
Higher power consumption
Improved oxygen transfer
Explanation - Micro‑bubbles usually require less power than large bubble systems for similar transfer rates.
Correct answer is: Higher power consumption
Q.79 What does the term 'shear rate' describe in a bioreactor?
Speed of gas flow
Velocity gradient in the liquid
Temperature gradient
Pressure gradient
Explanation - Shear rate quantifies how quickly fluid layers move relative to each other.
Correct answer is: Velocity gradient in the liquid
Q.80 Which of the following is a typical consequence of over‑agitation in a bioreactor?
Cell lysis
Reduced oxygen transfer
Decreased temperature
Lower pH
Explanation - Excessive agitation can shear fragile cells, causing them to rupture.
Correct answer is: Cell lysis
Q.81 What is the primary function of a dissolved oxygen sensor in a bioreactor?
To measure temperature
To monitor oxygen levels
To regulate pH
To detect pressure changes
Explanation - It provides real‑time data on oxygen availability for cells.
Correct answer is: To monitor oxygen levels
Q.82 Which of the following best describes the role of a 'pulsating aeration' strategy?
Constant gas flow
Intermittent gas bursts
Gradual increase in flow
No aeration
Explanation - Pulsating aeration alternates high and low flow to balance oxygen supply and shear.
Correct answer is: Intermittent gas bursts
Q.83 Which parameter directly affects the oxygen transfer rate in a bubble column?
Gas flow rate
Tank volume
Liquid density
All of the above
Explanation - All listed factors influence the gas‑liquid interface and mass transfer.
Correct answer is: All of the above
Q.84 What is the main advantage of using a magnetic stirrer in a small‑scale bioreactor?
High shear stress
Low cost and ease of use
Large volume handling
High power consumption
Explanation - Magnetic stirrers are inexpensive and simple to operate for lab‑scale cultures.
Correct answer is: Low cost and ease of use
Q.85 Which of the following is a key benefit of using a variable‑frequency drive (VFD) on an agitator?
Simplifies wiring
Reduces power consumption
Enables precise speed control
Increases noise level
Explanation - VFDs adjust motor speed accurately, optimizing mixing conditions.
Correct answer is: Enables precise speed control
Q.86 What does the term 'kLa' stand for in bioreactor design?
Kinetic limit area
Oxygen transfer coefficient
Liquid agitation speed
Pressure coefficient
Explanation - kLa quantifies how efficiently oxygen is transferred from gas to liquid.
Correct answer is: Oxygen transfer coefficient
Q.87 Which of the following is the most important consideration when scaling up a bioreactor aeration system?
Power supply voltage
Maintaining the same oxygen transfer rate
Changing the sparger material
Reducing the tank volume
Explanation - Consistent kLa ensures comparable oxygen availability across scales.
Correct answer is: Maintaining the same oxygen transfer rate
Q.88 Which component in a bioreactor aeration line measures the pressure drop across the sparger?
Pressure sensor
Temperature probe
pH probe
Dissolved oxygen probe
Explanation - Pressure sensors detect changes that indicate sparger blockage or fouling.
Correct answer is: Pressure sensor
Q.89 What is the effect of increasing the impeller diameter while maintaining the same tip speed?
Increases power consumption
Decreases power consumption
No change in power consumption
Increases impeller speed
Explanation - Power scales with the cube of impeller diameter for a constant tip speed.
Correct answer is: Increases power consumption
Q.90 Which of the following best describes the relationship between dissolved oxygen and cell growth?
High dissolved oxygen always slows growth
Low dissolved oxygen can limit growth
Dissolved oxygen has no effect
Dissolved oxygen is only relevant at high temperatures
Explanation - Insufficient oxygen limits aerobic cell metabolism, slowing proliferation.
Correct answer is: Low dissolved oxygen can limit growth
Q.91 What is the primary role of a gas‑liquid mass transfer model in bioprocess engineering?
To predict temperature gradients
To estimate oxygen transfer rates
To calculate pH changes
To determine impeller design
Explanation - Mass transfer models predict kLa and guide aeration design.
Correct answer is: To estimate oxygen transfer rates
Q.92 Which of the following is a common method to reduce shear stress on cells in a stirred bioreactor?
Increase agitation speed
Use a low‑shear impeller
Add a high‑pressure sparger
Increase gas flow rate
Explanation - Low‑shear impellers produce gentler mixing, protecting sensitive cells.
Correct answer is: Use a low‑shear impeller
Q.93 What is the most common method to measure the oxygen transfer coefficient (kLa) in a bioreactor?
Dissolved oxygen probe with step change
Temperature probe
pH probe
Conductivity probe
Explanation - A sudden O₂ step allows calculation of kLa from the O₂ response curve.
Correct answer is: Dissolved oxygen probe with step change
Q.94 Which of the following is a typical drawback of using a large‑bubble sparger?
High power consumption
Low oxygen transfer rate
High shear stress
All of the above
Explanation - Large bubbles reduce surface area, increase energy use, and create higher shear.
Correct answer is: All of the above
Q.95 What is the main advantage of using a parallel‑flow bioreactor for cell culture?
Simpler mixing
Higher shear stress
More uniform temperature
Reduced power consumption
Explanation - Parallel flow reduces dead zones, leading to a more uniform temperature field.
Correct answer is: More uniform temperature
Q.96 Which of the following is NOT a typical variable in the design of an aeration system?
Gas flow rate
Impeller speed
Sparger pore size
Ambient light intensity
Explanation - Light intensity does not affect aeration performance.
Correct answer is: Ambient light intensity
Q.97 Which sensor is used to measure the dissolved oxygen concentration in a bioreactor?
pH sensor
Temperature sensor
Dissolved oxygen sensor
Pressure sensor
Explanation - Dissolved oxygen sensors (Clark electrode) provide real‑time O₂ readings.
Correct answer is: Dissolved oxygen sensor
Q.98 What is the main purpose of a pressure relief valve in a bioreactor system?
Regulate temperature
Control agitation speed
Prevent over‑pressure
Maintain dissolved oxygen
Explanation - It opens when pressure exceeds safe limits to protect the vessel.
Correct answer is: Prevent over‑pressure
Q.99 Which of the following is an example of a low‑shear impeller used in mammalian cell culture?
Rushton turbine
Pitch‑fork impeller
Beckman turbine
Magnetic stir bar
Explanation - Pitch‑fork impellers provide gentle, planar flow suitable for delicate cells.
Correct answer is: Pitch‑fork impeller
Q.100 What is the effect of decreasing the temperature of the culture medium on dissolved oxygen solubility?
Increases solubility
Decreases solubility
No effect
Depends on oxygen concentration
Explanation - Lower temperatures increase the solubility of gases in liquids.
Correct answer is: Increases solubility
Q.101 Which component in a bioreactor aeration line is responsible for regulating gas composition?
Mass flow controller
Pressure gauge
Temperature sensor
pH probe
Explanation - Mass flow controllers adjust the flow of each gas, controlling the gas mix.
Correct answer is: Mass flow controller
Q.102 Which of the following is a key reason for using a micro‑bubble diffuser in a bioreactor?
Higher power consumption
Lower oxygen transfer efficiency
Reduced bubble coalescence
Increased shear stress
Explanation - Micro‑bubbles form and stay small, minimizing coalescence and improving transfer.
Correct answer is: Reduced bubble coalescence
Q.103 Which of the following best describes the function of a variable‑frequency drive (VFD) on a bioreactor agitator?
To increase motor speed automatically
To provide precise speed control
To reduce oxygen demand
To monitor dissolved oxygen
Explanation - VFDs allow continuous adjustment of speed, optimizing mixing and minimizing shear.
Correct answer is: To provide precise speed control
Q.104 Which of the following is a typical consequence of increasing gas flow rate in a bubble column?
Increased dissolved oxygen
Higher shear stress
Reduced bubble size
All of the above
Explanation - Higher flow boosts O₂ transfer, increases shear, and produces smaller bubbles.
Correct answer is: All of the above
Q.105 Which of the following is the most common way to measure power input in a stirred‑tank bioreactor?
Torque sensor
Temperature probe
pH meter
Pressure sensor
Explanation - Torque measurement allows calculation of power using P = T × ω.
Correct answer is: Torque sensor
Q.106 Which of the following factors does NOT directly influence the oxygen transfer coefficient (kLa) in a bioreactor?
Gas flow rate
Liquid viscosity
Tank geometry
Electrical voltage of the agitator
Explanation - kLa depends on gas–liquid physical parameters, not motor voltage.
Correct answer is: Electrical voltage of the agitator
Q.107 What is the main benefit of using a parallel‑flow sparger design?
Uniform gas distribution
Simplified maintenance
Lower power consumption
Higher shear stress
Explanation - Parallel‑flow spargers reduce local concentration gradients, improving homogeneity.
Correct answer is: Uniform gas distribution
Q.108 Which of the following is an advantage of using a magnetic stirrer for small‑scale bioreactor operations?
High shear stress
Low cost and ease of use
Large volume handling
High power consumption
Explanation - Magnetic stirrers are inexpensive and simple to operate for lab‑scale cultures.
Correct answer is: Low cost and ease of use
Q.109 Which electrical component protects the motor from voltage surges in a bioreactor system?
Fuse
Capacitor
Resistor
Inductor
Explanation - Capacitors smooth out voltage spikes, safeguarding motor components.
Correct answer is: Capacitor
Q.110 Which of the following is a typical use of a dissolved oxygen probe in a bioreactor?
Monitor temperature
Measure oxygen levels
Control agitation speed
Detect pressure changes
Explanation - It provides real‑time data on dissolved oxygen for process control.
Correct answer is: Measure oxygen levels
Q.111 Which of the following best describes the role of a sparger in a bioreactor?
To maintain temperature
To provide mixing
To deliver gas into the liquid
To measure pH
Explanation - A sparger introduces gas as fine bubbles for oxygen transfer.
Correct answer is: To deliver gas into the liquid
Q.112 Which of the following is a key benefit of using a micro‑bubble diffuser in a bioreactor?
Higher power consumption
Lower oxygen transfer efficiency
Reduced bubble coalescence
Increased shear stress
Explanation - Micro‑bubbles form and stay small, minimizing coalescence and improving transfer.
Correct answer is: Reduced bubble coalescence
Q.113 What is the primary function of a variable‑frequency drive (VFD) on a bioreactor agitator?
To increase motor speed automatically
To provide precise speed control
To reduce oxygen demand
To monitor dissolved oxygen
Explanation - VFDs allow continuous adjustment of speed, optimizing mixing and minimizing shear.
Correct answer is: To provide precise speed control
Q.114 Which of the following is a typical consequence of increasing gas flow rate in a bubble column?
Increased dissolved oxygen
Higher shear stress
Reduced bubble size
All of the above
Explanation - Higher flow boosts O₂ transfer, increases shear, and produces smaller bubbles.
Correct answer is: All of the above
Q.115 Which of the following is a common method to measure power input in a stirred‑tank bioreactor?
Torque sensor
Temperature probe
pH meter
Pressure sensor
Explanation - Torque measurement allows calculation of power using P = T × ω.
Correct answer is: Torque sensor
Q.116 Which of the following factors does NOT directly influence the oxygen transfer coefficient (kLa) in a bioreactor?
Gas flow rate
Liquid viscosity
Tank geometry
Electrical voltage of the agitator
Explanation - kLa depends on gas‑liquid physical parameters, not motor voltage.
Correct answer is: Electrical voltage of the agitator