Q.1 What is the primary kinetic model used to describe microbial growth in a well-mixed bioreactor when substrate concentration is high?
Monod model
Haldane model
Michaelis–Menten model
Linear growth model
Explanation - The Monod model is analogous to Michaelis–Menten kinetics and is commonly used to describe microbial growth when substrate is abundant and inhibition effects are negligible.
Correct answer is: Monod model
Q.2 In a fed‑batch reactor, what parameter primarily determines the time to reach the desired biomass concentration?
Feed rate
Initial substrate concentration
Volume change
Dilution rate
Explanation - The feed rate controls the supply of substrate; by adjusting it, the reactor can maintain the desired growth rate and biomass concentration over time.
Correct answer is: Feed rate
Q.3 Which kinetic model incorporates substrate inhibition at high concentrations?
Monod model
Haldane model
Logistic model
Chemostat model
Explanation - The Haldane model adds a substrate inhibition term (K_i) to the Monod equation, capturing the decrease in growth rate at high substrate levels.
Correct answer is: Haldane model
Q.4 The yield coefficient Y_X/S represents the ratio of what to what in bioreactor modeling?
Biomass produced to substrate consumed
Product formed to biomass produced
Biomass produced to product formed
Substrate consumed to biomass produced
Explanation - Y_X/S is defined as grams of biomass per gram of substrate consumed, reflecting conversion efficiency.
Correct answer is: Biomass produced to substrate consumed
Q.5 Which parameter is most directly related to oxygen transfer efficiency in a stirred tank bioreactor?
K_La
K_s
K_i
D
Explanation - K_La (volumetric mass transfer coefficient) quantifies the rate at which oxygen is transferred from gas to liquid, a key metric for aerobic processes.
Correct answer is: K_La
Q.6 In a Continuous Stirred Tank Reactor (CSTR), the steady‑state biomass concentration is given by which relationship?
X = μ / D
X = D / μ
X = μ / (D + μ)
X = (D + μ) / μ
Explanation - At steady state, the growth rate μ equals the dilution rate D times the biomass concentration X, giving X = μ/D.
Correct answer is: X = μ / D
Q.7 What does the parameter K_s in Monod kinetics represent?
Maximum specific growth rate
Half‑saturation constant
Substrate inhibition constant
Dilution rate
Explanation - K_s is the substrate concentration at which the growth rate is half of μ_max, indicating the affinity of cells for the substrate.
Correct answer is: Half‑saturation constant
Q.8 Which of the following is NOT typically considered a source of bioprocess variability?
Feed composition
Temperature fluctuations
Operator skill
Reactor volume
Explanation - Reactor volume is a fixed design parameter; variability arises from fluctuations in feed, temperature, and human factors.
Correct answer is: Reactor volume
Q.9 The term 'dilution rate' D in a chemostat is defined as:
Flow rate divided by volume
Volume divided by flow rate
Product concentration divided by time
Growth rate divided by substrate concentration
Explanation - D = F/V, representing the rate at which fresh medium is added relative to reactor volume, controlling residence time.
Correct answer is: Flow rate divided by volume
Q.10 What is the primary advantage of using a fed‑batch mode over a batch mode in bioreactor operations?
Lower risk of contamination
Simpler control strategy
Reduced substrate inhibition
Higher product yield per unit time
Explanation - Controlled feeding keeps substrate levels low, preventing inhibition and allowing higher overall yields compared to batch mode.
Correct answer is: Reduced substrate inhibition
Q.11 Which modeling approach involves solving ordinary differential equations to capture dynamic behavior?
Steady‑state analysis
Dynamic simulation
Statistical regression
Qualitative modeling
Explanation - Dynamic simulation uses ODEs to model time‑dependent changes in concentrations and biomass, offering detailed insight into reactor behavior.
Correct answer is: Dynamic simulation
Q.12 The parameter μ_max refers to:
Maximum specific substrate consumption rate
Maximum specific growth rate
Maximum dilution rate
Maximum oxygen transfer rate
Explanation - μ_max is the highest rate at which microorganisms can divide under optimal conditions.
Correct answer is: Maximum specific growth rate
Q.13 Which equation represents the logistic growth model?
dX/dt = μ_max X (1 - X/K)
dX/dt = μ_max X / (K_s + S)
dX/dt = μ_max X - (X^2)/K_i
dX/dt = μ_max X / (K_s + S + S^2/K_i)
Explanation - The logistic model describes growth limited by carrying capacity K, with a term (1 - X/K) reducing growth as biomass increases.
Correct answer is: dX/dt = μ_max X (1 - X/K)
Q.14 In a CSTR, how does increasing the dilution rate D affect the steady‑state product concentration for a product formed at a constant specific rate r_p?
It increases proportionally
It remains constant
It decreases inversely
It increases only up to a threshold
Explanation - Higher D removes product faster; steady‑state product concentration is r_p/D, so it decreases as D increases.
Correct answer is: It decreases inversely
Q.15 Which of the following is a typical value of K_La for a high‑efficiency stirred tank bioreactor?
0.1 h⁻¹
1.5 h⁻¹
10 h⁻¹
100 h⁻¹
Explanation - High‑efficiency systems often achieve K_La values around 10 h⁻¹, reflecting rapid oxygen transfer.
Correct answer is: 10 h⁻¹
Q.16 What is the main reason for using a two‑compartment model in bioreactor kinetic studies?
To represent temperature gradients
To separate cell and substrate dynamics
To model gas‑liquid mass transfer separately
To account for two microbial species
Explanation - A two‑compartment model divides the system into liquid and gas phases, enabling explicit representation of mass transfer rates.
Correct answer is: To model gas‑liquid mass transfer separately
Q.17 Which parameter is directly proportional to the maximum biomass concentration achievable in a chemostat?
μ_max
K_s
D
Y_X/S
Explanation - A higher yield coefficient Y_X/S converts more substrate into biomass, raising the steady‑state biomass concentration.
Correct answer is: Y_X/S
Q.18 Which term is used to describe the loss of cells due to cell death or settling in a reactor?
Decay rate
Dilution rate
Transfer rate
Inhibition constant
Explanation - The decay rate (k_d) accounts for cell loss mechanisms such as death or sedimentation, reducing net biomass growth.
Correct answer is: Decay rate
Q.19 The Monod equation for growth rate μ can be written as:
μ = μ_max S / (K_s + S)
μ = μ_max S / (K_i + S)
μ = μ_max (K_s + S) / S
μ = μ_max (S + K_s) / (S + K_i)
Explanation - The Monod model expresses growth as a saturating function of substrate concentration S, with μ_max and K_s.
Correct answer is: μ = μ_max S / (K_s + S)
Q.20 Which of the following best describes a fed‑batch reactor operation mode?
Constant volume, continuous feed, no outflow
Constant volume, continuous feed, continuous outflow
Variable volume, continuous feed, continuous outflow
Variable volume, no feed, constant outflow
Explanation - In fed‑batch, volume is maintained by feeding and no liquid is removed, except for sampling.
Correct answer is: Constant volume, continuous feed, no outflow
Q.21 What does the term 'product inhibition' refer to in bioprocess modeling?
Inhibition of cell growth by substrate depletion
Inhibition of enzyme activity by the product
Inhibition of substrate uptake by product accumulation
Inhibition of oxygen transfer by product presence
Explanation - Product inhibition occurs when the product interferes with enzymes or transport mechanisms, reducing growth or production rates.
Correct answer is: Inhibition of enzyme activity by the product
Q.22 Which parameter in the Haldane model indicates the substrate concentration at which half of the maximum inhibition occurs?
K_s
K_i
μ_max
Y_X/S
Explanation - K_i (inhibition constant) denotes the substrate concentration at which the inhibitory effect is half of its maximum.
Correct answer is: K_i
Q.23 Which equation represents the mass balance for substrate in a CSTR at steady state?
F_in S_in - F_out S - V μ X = 0
F_in S_in - F_out S + μ X = 0
F_in S_in + F_out S - μ X = 0
F_in S_in - F_out S + μ X = 0
Explanation - The mass balance equates substrate input minus output and consumption by cells to zero at steady state.
Correct answer is: F_in S_in - F_out S - V μ X = 0
Q.24 Which of the following is a direct consequence of operating a CSTR at a dilution rate D > μ_max?
Biomass concentration increases exponentially
Biomass concentration reaches a new steady state
Biomass concentration becomes zero (washout)
Product concentration becomes negative
Explanation - When D exceeds μ_max, cells cannot keep up with removal and wash out of the reactor.
Correct answer is: Biomass concentration becomes zero (washout)
Q.25 Which parameter represents the efficiency of converting substrate into product in a fermentation?
Y_P/S
Y_X/S
Y_P/X
Y_X/P
Explanation - Y_P/S is the product yield per unit substrate consumed, indicating conversion efficiency.
Correct answer is: Y_P/S
Q.26 In a reactor simulation, why are stochastic models sometimes preferred over deterministic models?
They are computationally faster
They capture random fluctuations in cell populations
They always produce more accurate results
They eliminate the need for parameter estimation
Explanation - Stochastic models account for inherent randomness in biological systems, such as cell‑to‑cell variability.
Correct answer is: They capture random fluctuations in cell populations
Q.27 The term 'biomass yield' typically refers to:
Biomass concentration per unit reactor volume
Biomass produced per unit substrate consumed
Biomass produced per unit product formed
Biomass produced per unit time
Explanation - Yield expresses the efficiency of substrate conversion into biomass.
Correct answer is: Biomass produced per unit substrate consumed
Q.28 Which reactor type is characterized by a constant volume and continuous inflow and outflow of liquid?
Fed‑batch reactor
Continuous Stirred Tank Reactor (CSTR)
Plug Flow Reactor (PFR)
Batch reactor
Explanation - CSTRs maintain constant volume by balancing inflow and outflow while mixing uniformly.
Correct answer is: Continuous Stirred Tank Reactor (CSTR)
Q.29 In a PFR, the residence time τ is given by:
V / F
F / V
V × F
F × V
Explanation - Residence time τ = volume / volumetric flow rate, representing average time a fluid element spends in the reactor.
Correct answer is: V / F
Q.30 Which kinetic model is most appropriate when a product acts as a feedback inhibitor of its own synthesis?
Monod model
Haldane model
Product inhibition model
Mass transfer model
Explanation - Product inhibition models explicitly include terms that reduce synthesis rates as product concentration increases.
Correct answer is: Product inhibition model
Q.31 What is the effect of increasing the stirring speed on K_La?
K_La decreases
K_La remains unchanged
K_La increases
K_La becomes zero
Explanation - Higher stirring enhances gas‑liquid mixing, improving oxygen transfer and raising K_La.
Correct answer is: K_La increases
Q.32 Which of the following is a key assumption of the Monod kinetic model?
Substrate concentration is constant
Cells are of uniform size
Product is not present
Cells are at equilibrium
Explanation - Monod assumes that substrate concentration does not limit growth; it is a simplification for modeling.
Correct answer is: Substrate concentration is constant
Q.33 The parameter 'D' in a fed‑batch reactor controls:
Dilution of substrate
Rate of feed addition
Biomass decay rate
Oxygen transfer rate
Explanation - In fed‑batch, D is used to define the feed rate relative to reactor volume, controlling how fast substrate is added.
Correct answer is: Rate of feed addition
Q.34 Which of the following best describes the term 'yield coefficient' in bioprocess modeling?
Ratio of product to biomass
Ratio of substrate to biomass
Ratio of biomass to substrate
Ratio of product to substrate
Explanation - Yield coefficient Y_X/S is defined as grams of biomass per gram of substrate consumed.
Correct answer is: Ratio of biomass to substrate
Q.35 In a chemostat, what condition must be met for a stable steady‑state to exist?
D > μ_max
D < μ_max
D = μ_max
D is unrelated to μ_max
Explanation - Steady‑state stability requires the dilution rate be less than the maximum specific growth rate.
Correct answer is: D < μ_max
Q.36 What is the primary purpose of performing a parameter estimation step in kinetic modeling?
To design the reactor geometry
To determine values of kinetic constants from data
To validate the bioprocess
To calculate energy consumption
Explanation - Parameter estimation fits experimental data to kinetic equations, extracting values like μ_max, K_s, etc.
Correct answer is: To determine values of kinetic constants from data
Q.37 Which of the following is NOT a typical control variable in a fed‑batch reactor?
pH
Temperature
Light intensity
Oxygen concentration
Explanation - While photobioreactors use light, most fed‑batch fermentations do not rely on light; pH, temperature, and O₂ are typical controls.
Correct answer is: Light intensity
Q.38 In the context of bioreactor modeling, what does the term 'stoichiometric coefficient' refer to?
Number of cells per reactor volume
Coefficient in the balanced reaction equation
Rate of mass transfer
Yield of product per substrate
Explanation - Stoichiometric coefficients represent the proportions of reactants and products in a balanced chemical or biochemical equation.
Correct answer is: Coefficient in the balanced reaction equation
Q.39 Which reactor design is best suited for high‑viscosity cultures?
CSTR with high agitation
PFR with long residence time
Fed‑batch with slow feeding
Plug‑flow with minimal mixing
Explanation - High agitation improves mixing and mass transfer in viscous media, making CSTRs preferable.
Correct answer is: CSTR with high agitation
Q.40 Which of the following is a measure of reactor performance in terms of substrate utilization?
Specific growth rate
Oxygen transfer rate
Substrate uptake rate
Dilution rate
Explanation - Substrate uptake rate quantifies how quickly cells consume substrate, reflecting process efficiency.
Correct answer is: Substrate uptake rate
Q.41 The term 'maximum specific growth rate' (μ_max) is expressed in units of:
1/h
g/L
mmol/(g·h)
Pa·s
Explanation - μ_max is a rate constant indicating growth per unit time, typically expressed per hour.
Correct answer is: 1/h
Q.42 Which of the following best describes a 'washout' phenomenon?
Cells grow to maximum density
Substrate is completely consumed
Cells are removed faster than they grow
Product is removed faster than it is produced
Explanation - Washout occurs when the dilution rate exceeds the growth rate, leading to zero biomass concentration.
Correct answer is: Cells are removed faster than they grow
Q.43 In a fed‑batch process, what is the primary advantage of using a 'zero‑inoculum' strategy?
Reduces initial cell density
Increases product yield
Avoids contamination from inoculum
Simplifies feed formulation
Explanation - Zero‑inoculum reduces the risk of introducing contaminants by eliminating the inoculation step.
Correct answer is: Avoids contamination from inoculum
Q.44 Which kinetic model is characterized by a quadratic term in substrate concentration?
Monod model
Haldane model
Product inhibition model
Linear model
Explanation - The Haldane equation includes an S² term in the denominator, representing inhibition by high substrate levels.
Correct answer is: Haldane model
Q.45 The parameter K_s in Monod kinetics is analogous to which enzyme kinetic constant?
K_m
K_i
K_d
K_p
Explanation - K_s represents the substrate concentration at half‑maximal growth, analogous to Michaelis constant K_m in enzyme kinetics.
Correct answer is: K_m
Q.46 Which of the following is a key factor influencing oxygen transfer rate?
Solute concentration
Agitation speed
Substrate type
Product yield
Explanation - Higher agitation enhances gas‑liquid contact, increasing the oxygen transfer rate.
Correct answer is: Agitation speed
Q.47 In a dynamic simulation of a bioreactor, which numerical method is often used to integrate ODEs?
Runge‑Kutta method
Euler method
Gaussian elimination
Newton‑Raphson method
Explanation - Runge‑Kutta methods provide accurate integration of ordinary differential equations common in reactor modeling.
Correct answer is: Runge‑Kutta method
Q.48 Which parameter is critical for determining the onset of the exponential growth phase in a batch culture?
Initial substrate concentration
Initial biomass concentration
Dilution rate
Product formation rate
Explanation - Sufficient substrate is needed for cells to enter exponential growth; low substrate delays this phase.
Correct answer is: Initial substrate concentration
Q.49 What does the symbol 'X' represent in bioreactor mass balance equations?
Cell concentration
Product concentration
Substrate concentration
Volume
Explanation - In bioprocess notation, X denotes biomass (cells) concentration.
Correct answer is: Cell concentration
Q.50 Which of the following describes the 'substrate utilization rate' in a batch reactor?
dS/dt = -μ X
dS/dt = μ X
dS/dt = μ X - F/V
dS/dt = F/V - μ X
Explanation - Negative sign indicates consumption of substrate by cells at rate μ X.
Correct answer is: dS/dt = -μ X
Q.51 In the context of bioreactor design, what is the 'liquid holdup'?
Volume of gas trapped in the liquid
Volume of liquid retained in the reactor
Time spent by a liquid element in the reactor
Volume of liquid per unit reactor surface area
Explanation - Liquid holdup refers to the effective volume of liquid present in a gas‑liquid system.
Correct answer is: Volume of liquid retained in the reactor
Q.52 Which of the following is a characteristic of a 'plug‑flow reactor'?
Uniform concentration throughout
No axial mixing
Constant residence time for all fluid elements
High turbulence
Explanation - PFRs assume no mixing in the flow direction, leading to concentration gradients along the reactor length.
Correct answer is: No axial mixing
Q.53 The term 'logistic growth' is most closely related to which biological phenomenon?
Exponential growth with unlimited resources
Growth limited by carrying capacity
Growth with substrate inhibition
Growth with product inhibition
Explanation - Logistic growth incorporates a carrying capacity that limits population growth as density increases.
Correct answer is: Growth limited by carrying capacity
Q.54 What is the main function of a 'sparger' in a bioreactor?
Stir the liquid
Introduce gas into the liquid
Measure pH
Control temperature
Explanation - Spargers disperse gas (e.g., oxygen) as fine bubbles into the liquid for mass transfer.
Correct answer is: Introduce gas into the liquid
Q.55 Which equation describes the relationship between oxygen transfer rate (OTR) and volumetric mass transfer coefficient (K_La)?
OTR = K_La × C_O₂
OTR = K_La × (C_O₂* - C_O₂)
OTR = K_La / (C_O₂* - C_O₂)
OTR = K_La × (C_O₂ + C_O₂*)
Explanation - OTR is proportional to the product of K_La and the driving force (difference between saturation and actual concentration).
Correct answer is: OTR = K_La × (C_O₂* - C_O₂)
Q.56 Which of the following is a common method to estimate kinetic parameters from experimental data?
Non‑linear regression
Linear regression on transformed data
Principal component analysis
Fourier transform
Explanation - Kinetic models often require non‑linear regression because the equations are non‑linear in parameters.
Correct answer is: Non‑linear regression
Q.57 In the Monod model, what happens to μ when substrate concentration S → 0?
μ approaches μ_max
μ approaches 0
μ becomes negative
μ approaches infinity
Explanation - When S is very low, growth rate tends to zero because substrate is limiting.
Correct answer is: μ approaches 0
Q.58 Which of the following is NOT typically a design consideration for a high‑volume bioreactor?
Material of construction
Aeration strategy
Lighting system
Sterilization method
Explanation - Most microbial fermentations are dark; lighting is usually irrelevant except for phototrophic cultures.
Correct answer is: Lighting system
Q.59 What does the symbol 'S' denote in bioprocess equations?
Product concentration
Substrate concentration
Biomass concentration
Solvent concentration
Explanation - Standard notation uses S for substrate, X for biomass, P for product.
Correct answer is: Substrate concentration
Q.60 Which of the following best describes 'batch mode' operation?
Continuous addition of substrate
Continuous removal of product
Closed system with no continuous input or output
Continuous monitoring of pH
Explanation - Batch operation involves starting with initial conditions and letting the process evolve without further input or removal.
Correct answer is: Closed system with no continuous input or output
Q.61 In a CSTR, why does the product concentration usually decrease with increasing dilution rate D?
Product is degraded faster
Cells consume product at higher rates
Product is washed out faster
Product solubility decreases
Explanation - Higher D means the product is removed from the reactor more quickly, lowering its steady‑state concentration.
Correct answer is: Product is washed out faster
Q.62 Which parameter indicates the maximum rate of substrate consumption per unit biomass?
μ_max
Y_X/S
k_d
q_s
Explanation - Specific substrate consumption rate q_s (g_s/g_X·h) defines how fast each unit of biomass consumes substrate.
Correct answer is: q_s
Q.63 What is the purpose of using a 'chemostat' in bioprocess research?
To maintain constant product concentration
To study microbial growth at steady state under controlled conditions
To accelerate product formation
To reduce oxygen transfer limitations
Explanation - Chemostats provide a constant environment, allowing observation of microbial physiology at steady state.
Correct answer is: To study microbial growth at steady state under controlled conditions
Q.64 The 'substrate inhibition constant' K_i in the Haldane model is associated with:
Maximum growth rate
Half‑saturation of substrate
Product inhibition
Substrate inhibition effect
Explanation - K_i quantifies the concentration at which substrate starts inhibiting growth.
Correct answer is: Substrate inhibition effect
Q.65 Which of the following is a common method to measure oxygen transfer coefficient K_La?
Gas‑phase pressure drop
Dynamic gassing‑out method
Spectrophotometric assay
pH probe measurement
Explanation - This method measures the rate at which dissolved oxygen rises after a sudden change in gas composition.
Correct answer is: Dynamic gassing‑out method
Q.66 In a fed‑batch reactor, what is the typical trend of substrate concentration over time?
Constant
Monotonically increasing
Monotonically decreasing
Oscillatory
Explanation - Even though substrate is added, consumption generally outpaces feeding, leading to a gradual decline.
Correct answer is: Monotonically decreasing
Q.67 Which of the following best describes the 'carryover effect' in fed‑batch operations?
Residual cells from the previous batch
Unreacted substrate remaining in the reactor
Product carried over between batches
Temperature fluctuations carried into the next batch
Explanation - Carryover refers to residual materials from the previous batch that influence the next batch’s performance.
Correct answer is: Unreacted substrate remaining in the reactor
Q.68 Which kinetic model introduces a quadratic term to capture product inhibition effects?
Monod model
Haldane model
Product inhibition model
Linear growth model
Explanation - Product inhibition equations often contain a P² term to reflect nonlinear inhibition by product concentration.
Correct answer is: Product inhibition model
Q.69 What does the term 'steady‑state' refer to in the context of a CSTR?
Concentrations vary sinusoidally
Concentrations remain constant over time
Biomass concentration is zero
Substrate is completely consumed
Explanation - At steady state, all inlet and outlet rates balance, keeping concentrations unchanged.
Correct answer is: Concentrations remain constant over time
Q.70 Which parameter is directly proportional to the volumetric flow rate in a CSTR?
Dilution rate D
Substrate concentration S
Biomass concentration X
Product concentration P
Explanation - Dilution rate D = F/V, thus directly proportional to flow rate F.
Correct answer is: Dilution rate D
Q.71 In bioreactor modeling, the 'substrate uptake rate' q_s is typically expressed as:
g_s/(g_X·h)
g_X/(g_s·h)
g_P/(g_X·h)
g_X/(g_P·h)
Explanation - q_s is the specific substrate consumption rate per unit biomass.
Correct answer is: g_s/(g_X·h)
Q.72 Which of the following is a major challenge in modeling photobioreactors?
Temperature control
Light penetration
pH drift
Sterilization
Explanation - Light intensity decreases with depth, causing non‑uniform growth conditions.
Correct answer is: Light penetration
Q.73 Which term in the Monod equation represents the maximum specific growth rate?
μ_max
K_s
S
X
Explanation - μ_max is the asymptotic limit of the growth rate as substrate becomes abundant.
Correct answer is: μ_max
Q.74 In a PFR, the concentration of substrate at the outlet can be calculated using:
X_out = X_in * exp(-k τ)
S_out = S_in * (1 - k τ)
P_out = P_in + k τ
S_out = S_in / (1 + k τ)
Explanation - The plug‑flow model gives exponential decay of concentration with residence time τ.
Correct answer is: X_out = X_in * exp(-k τ)
Q.75 Which parameter in a bioreactor design represents the ability of the reactor to transfer oxygen from gas to liquid?
K_La
K_s
K_i
μ_max
Explanation - K_La quantifies the mass transfer coefficient for oxygen across the gas‑liquid interface.
Correct answer is: K_La
Q.76 What is the primary goal of a parameter estimation step in bioprocess modeling?
Design the bioreactor geometry
Fit model equations to experimental data
Validate the control strategy
Predict product quality
Explanation - Parameter estimation determines model constants that best represent the observed data.
Correct answer is: Fit model equations to experimental data
Q.77 In a fed‑batch reactor, the 'feed concentration' refers to:
Concentration of substrate in the feed stream
Concentration of cells in the feed stream
Concentration of product in the feed stream
Concentration of buffer in the feed stream
Explanation - Feed concentration is the amount of substrate added per unit volume of feed.
Correct answer is: Concentration of substrate in the feed stream
Q.78 Which of the following is NOT a typical assumption when using the Monod model?
Substrate is limiting
Cells are homogeneous
Product inhibition is negligible
Biomass concentration is constant
Explanation - Monod allows biomass to grow; it does not assume constant concentration.
Correct answer is: Biomass concentration is constant
Q.79 What does the symbol 'D' represent in a chemostat?
Dilution rate
Diffusion coefficient
Displacement
Depletion rate
Explanation - D is defined as volumetric flow rate divided by reactor volume, indicating removal speed.
Correct answer is: Dilution rate
Q.80 Which parameter is used to describe the affinity of cells for substrate?
K_s
K_i
μ_max
Y_X/S
Explanation - A small K_s indicates high affinity for substrate; large K_s indicates low affinity.
Correct answer is: K_s
Q.81 In the context of mass transfer, the term 'air‑to‑liquid ratio' (AR) influences:
Oxygen transfer rate
Substrate consumption rate
Product formation rate
Biomass decay rate
Explanation - Higher AR increases the gas volume per liquid volume, improving oxygen transfer.
Correct answer is: Oxygen transfer rate
Q.82 Which equation best describes the growth of biomass in a batch reactor without product inhibition?
dX/dt = μ X
dX/dt = μ_max X / (K_s + S)
dX/dt = μ X (1 - X/K)
dX/dt = μ X / (1 + P/K_i)
Explanation - In a simple batch with no inhibition, the growth rate is μ times the biomass.
Correct answer is: dX/dt = μ X
Q.83 What is a common cause of product inhibition in a fed‑batch fermentation?
Low pH
High temperature
High product concentration
Low agitation speed
Explanation - Excess product can inhibit enzymes or transport mechanisms, slowing production.
Correct answer is: High product concentration
Q.84 Which of the following is a typical characteristic of a high‑affinity substrate transporter?
Large K_s
Small K_s
Large μ_max
Small μ_max
Explanation - Small K_s means the transporter efficiently uptakes substrate even at low concentrations.
Correct answer is: Small K_s
Q.85 Which of the following is NOT part of the Monod kinetic model?
μ_max
K_s
K_i
S
Explanation - K_i is part of the Haldane model; Monod includes only μ_max, K_s, and S.
Correct answer is: K_i
Q.86 In a PFR, the mass balance for substrate is:
F_in S_in - F_out S = V dS/dt
F_in S_in - F_out S = V dS/dx
F_in S_in - F_out S = 0
F_in S_in + F_out S = V dS/dt
Explanation - In plug‑flow, substrate concentration changes along the reactor length (x), not over time.
Correct answer is: F_in S_in - F_out S = V dS/dx
Q.87 The 'volume of the bioreactor' is used in which of the following equations?
V = F/D
V = D/F
V = μ X
V = K_La × C_O₂
Explanation - Dilution rate D equals flow rate F divided by volume V; rearranging gives V = F/D.
Correct answer is: V = F/D
Q.88 Which parameter is critical for ensuring that a batch culture does not experience substrate inhibition?
Feed concentration
Initial substrate concentration
Dilution rate
Biomass yield
Explanation - Too high an initial substrate concentration can lead to inhibition; controlling it prevents that.
Correct answer is: Initial substrate concentration
Q.89 Which of the following best describes the 'logistic growth equation' in bioprocess modeling?
dX/dt = μ X
dX/dt = μ X (1 - X/K)
dX/dt = μ X / (K_s + S)
dX/dt = μ X / (1 + P/K_i)
Explanation - The logistic equation includes a carrying capacity term (K) that limits growth as X increases.
Correct answer is: dX/dt = μ X (1 - X/K)
Q.90 In the Haldane model, the term S^2 in the denominator reflects:
Substrate affinity
Substrate inhibition
Product inhibition
Biomass decay
Explanation - The quadratic term captures the negative effect of high substrate levels on growth.
Correct answer is: Substrate inhibition
Q.91 What does the symbol 'q_p' represent in bioprocess modeling?
Specific product formation rate
Specific substrate uptake rate
Specific biomass growth rate
Specific oxygen uptake rate
Explanation - q_p indicates product produced per unit biomass per unit time.
Correct answer is: Specific product formation rate
Q.92 Which parameter is directly related to the maximum rate of cell division in a bioreactor?
μ_max
K_s
K_i
q_s
Explanation - μ_max is the highest specific growth rate achievable by the cells.
Correct answer is: μ_max
Q.93 In a CSTR, the steady‑state concentration of product P is:
P = q_p / D
P = D / q_p
P = q_p * D
P = D * q_p
Explanation - At steady state, production rate equals removal rate: q_p X = D P, so P = q_p X / D. For X = 1, P = q_p / D.
Correct answer is: P = q_p / D
Q.94 Which of the following is a key advantage of using a 'continuous stirred‑tank reactor (CSTR)' for scale‑up?
Uniform mixing throughout the reactor
Easy temperature control
Minimal oxygen transfer issues
High product concentrations
Explanation - CSTRs provide homogenous conditions, which simplifies scale‑up by reducing concentration gradients.
Correct answer is: Uniform mixing throughout the reactor
Q.95 Which parameter indicates the rate at which substrate is consumed by a single unit of biomass?
q_s
q_p
μ_max
D
Explanation - q_s is the specific substrate consumption rate, measured in g_s/g_X·h.
Correct answer is: q_s
Q.96 In a fed‑batch reactor, why is it important to maintain a constant pH?
It prevents product precipitation
It stabilizes enzyme activity
It improves mixing
It reduces oxygen solubility
Explanation - Enzyme activity and cell metabolism are pH‑dependent; maintaining pH keeps growth optimal.
Correct answer is: It stabilizes enzyme activity
Q.97 Which of the following best describes a 'batch reactor' operation mode?
Continuous addition of feed and removal of product
Continuous feed with no removal of liquid
Closed system with no continuous input or output
Continuous removal of product with no feed
Explanation - Batch operation starts with initial conditions and does not add or remove material during operation.
Correct answer is: Closed system with no continuous input or output
Q.98 Which of the following equations represents the specific oxygen uptake rate (q_O2) in terms of K_La and dissolved oxygen concentration?
q_O2 = K_La * C_O2*
q_O2 = K_La * (C_O2* - C_O2)
q_O2 = K_La / (C_O2* - C_O2)
q_O2 = K_La * C_O2
Explanation - Oxygen uptake is driven by the difference between saturation and actual dissolved oxygen.
Correct answer is: q_O2 = K_La * (C_O2* - C_O2)
Q.99 What is the effect of increasing the dilution rate D on the steady‑state biomass concentration in a CSTR?
Increases biomass concentration
Decreases biomass concentration
Leaves biomass concentration unchanged
Causes biomass concentration to oscillate
Explanation - Higher D means cells are removed faster, reducing steady‑state biomass.
Correct answer is: Decreases biomass concentration
Q.100 Which of the following best describes 'product inhibition' in a bioreactor?
Product accumulates and inhibits cell growth
Product degrades over time
Product is removed by the dilution rate
Product is not produced in batch mode
Explanation - High concentrations of product can feedback and reduce enzyme activity or growth.
Correct answer is: Product accumulates and inhibits cell growth
Q.101 In a fed‑batch reactor, what is the typical trend of the dilution rate over time?
Constant
Increasing
Decreasing
Oscillating
Explanation - As volume increases due to feeding, maintaining a constant flow rate leads to an increasing dilution rate.
Correct answer is: Increasing
Q.102 Which equation describes the substrate concentration dynamics in a CSTR?
dS/dt = (S_in - S)/τ - (1/Y_X/S) μ X
dS/dt = μ X - (S_in - S)/τ
dS/dt = μ X / τ - (S_in - S)
dS/dt = (S_in - S) - μ X τ
Explanation - Substrate change equals inflow minus outflow plus consumption by cells, where τ = 1/D.
Correct answer is: dS/dt = (S_in - S)/τ - (1/Y_X/S) μ X
Q.103 Which parameter is used to describe the efficiency of converting substrate into product per unit biomass?
Y_P/X
Y_X/P
Y_X/S
Y_P/S
Explanation - Y_P/X measures grams of product per gram of biomass, indicating conversion per cell mass.
Correct answer is: Y_P/X
Q.104 In a PFR, what is the typical relationship between substrate concentration and reactor length?
Substrate concentration increases linearly
Substrate concentration decreases exponentially
Substrate concentration remains constant
Substrate concentration oscillates
Explanation - In plug‑flow, substrate is consumed as fluid moves forward, following an exponential decay.
Correct answer is: Substrate concentration decreases exponentially
Q.105 What does the 'carrying capacity' K refer to in logistic growth modeling?
Maximum substrate concentration
Maximum product concentration
Maximum biomass concentration
Maximum dilution rate
Explanation - K is the asymptotic limit of biomass concentration when growth is limited by resources.
Correct answer is: Maximum biomass concentration
Q.106 Which of the following is NOT a typical input parameter for kinetic modeling of a bioreactor?
Initial biomass concentration
Feed composition
Agitation speed
Substrate yield coefficient
Explanation - While agitation influences mass transfer, it is not a kinetic parameter in the Monod or Haldane equations.
Correct answer is: Agitation speed
Q.107 In a CSTR, which term represents the removal of product by the dilution rate?
D P
P/D
D / P
P D
Explanation - Product outflow is proportional to product concentration times dilution rate: D P.
Correct answer is: D P
Q.108 Which of the following best describes the 'substrate inhibition constant' K_i?
Concentration at which half of the maximum growth occurs
Concentration at which substrate stops inhibiting growth
Concentration at which inhibition is half of its maximum
Maximum substrate concentration
Explanation - K_i indicates the level of substrate where its inhibitory effect is half of the maximum.
Correct answer is: Concentration at which inhibition is half of its maximum
Q.109 The 'biomass yield coefficient' Y_X/S is expressed in units of:
g_X/g_S
g_S/g_X
g_P/g_X
g_X/g_P
Explanation - Yield is defined as mass of biomass produced per mass of substrate consumed.
Correct answer is: g_X/g_S
Q.110 Which of the following is a common method to estimate the growth rate μ from experimental data?
Plotting ln(X) versus time
Plotting X versus time
Plotting S versus time
Plotting P versus time
Explanation - During exponential growth, ln(X) vs time is linear with slope μ.
Correct answer is: Plotting ln(X) versus time
Q.111 What is the main purpose of using a 'fed‑batch' mode in a bioprocess?
To keep substrate concentrations low
To increase initial cell density
To eliminate the need for pH control
To reduce product yield
Explanation - Feeding continuously keeps substrate below inhibitory levels, improving yield.
Correct answer is: To keep substrate concentrations low
Q.112 Which parameter is commonly used to describe the rate of oxygen transfer in a bioreactor?
K_La
K_s
K_i
q_O2
Explanation - K_La is the volumetric mass transfer coefficient for oxygen.
Correct answer is: K_La
Q.113 The term 'saturation concentration' C_O2* refers to:
Maximum product concentration
Dissolved oxygen concentration at equilibrium with gas phase
Substrate concentration at equilibrium with gas phase
Oxygen concentration in the gas phase
Explanation - C_O2* is the equilibrium dissolved oxygen when the liquid and gas are at the same partial pressure.
Correct answer is: Dissolved oxygen concentration at equilibrium with gas phase