Q.1 What does the yield coefficient Y_X/S represent in a microbial batch culture?
Grams of substrate consumed per gram of cells produced
Grams of cells produced per gram of substrate consumed
Moles of product formed per mole of substrate consumed
Moles of substrate consumed per mole of product formed
Explanation - Y_X/S is defined as the mass of biomass formed (g) per mass of substrate utilized (g).
Correct answer is: Grams of cells produced per gram of substrate consumed
Q.2 In the Luedeking‑Piret model, the term α·X·µ accounts for which type of product formation?
Non‑growth‑associated product formation
Growth‑associated product formation
Substrate inhibition
Product degradation
Explanation - The α·X·µ term links product formation rate to the specific growth rate µ, describing growth‑associated synthesis.
Correct answer is: Growth‑associated product formation
Q.3 If a bioprocess follows the Pirt equation q_S = m_s + (1/Y_X/S)·µ, what does m_s represent?
Maximum specific growth rate
Maintenance coefficient (substrate used for non‑growth activities)
Yield coefficient for product formation
Biomass concentration at steady state
Explanation - m_s is the maintenance coefficient, the substrate consumption not linked to growth.
Correct answer is: Maintenance coefficient (substrate used for non‑growth activities)
Q.4 A culture has a specific growth rate (µ) of 0.2 h⁻¹ and a biomass concentration (X) of 5 g/L. What is the specific growth rate expression µ = (1/X)(dX/dt) equal to?
0.04 h⁻¹
1.0 h⁻¹
0.2 h⁻¹
5.0 h⁻¹
Explanation - µ = (1/X)(dX/dt) is given directly as 0.2 h⁻¹; the numbers confirm the definition.
Correct answer is: 0.2 h⁻¹
Q.5 In a fed‑batch process, the substrate feed rate F_s is adjusted to keep µ constant. Which term in the mass balance equation dS/dt = (F_s/V)(S_f - S) - q_S·X is directly controlled?
q_S
X
F_s
V
Explanation - The feed rate F_s is the controllable variable that influences substrate concentration and therefore µ.
Correct answer is: F_s
Q.6 For a growth‑associated product, the specific product formation rate q_P is proportional to:
Biomass concentration only
Specific growth rate µ only
Both X and µ
Substrate concentration S
Explanation - Growth‑associated product formation follows q_P = α·µ, where α is a constant.
Correct answer is: Specific growth rate µ only
Q.7 Which of the following statements is true for a non‑growth‑associated product?
Its formation rate is highest during the exponential phase.
It is directly proportional to the specific growth rate µ.
Its formation rate is independent of µ and often described by a constant β.
It requires substrate concentration to be above the inhibition threshold.
Explanation - Non‑growth‑associated product formation follows q_P = β, where β is a constant independent of µ.
Correct answer is: Its formation rate is independent of µ and often described by a constant β.
Q.8 If the biomass yield Y_X/S = 0.5 g/g and the substrate consumption rate q_S = 0.8 g g⁻¹ h⁻¹, what is the specific growth rate µ?
0.4 h⁻¹
0.6 h⁻¹
1.6 h⁻¹
0.25 h⁻¹
Explanation - µ = Y_X/S × (q_S – m_s). Assuming negligible maintenance (m_s≈0), µ = 0.5 × 0.8 = 0.4 h⁻¹.
Correct answer is: 0.4 h⁻¹
Q.9 In a chemostat operating at dilution rate D, steady‑state is achieved when:
µ > D
µ = D
µ < D
µ = 0
Explanation - At steady state in a continuous culture, the specific growth rate equals the dilution rate.
Correct answer is: µ = D
Q.10 A bioreactor produces 10 g of product per liter from 20 g of substrate per liter. What is the product‑to‑substrate yield Y_P/S?
0.2 g/g
2.0 g/g
0.5 g/g
5.0 g/g
Explanation - Y_P/S = mass of product / mass of substrate = 10/20 = 0.5 g/g.
Correct answer is: 0.5 g/g
Q.11 Which kinetic model best describes substrate inhibition at high substrate concentrations?
Monod model
Andrews (Haldane) model
Pirt model
Luedeking‑Piret model
Explanation - The Andrews model incorporates an inhibition term to account for high substrate levels.
Correct answer is: Andrews (Haldane) model
Q.12 In the Monod equation µ = µ_max·S/(K_s + S), what does K_s represent?
Maximum specific growth rate
Substrate concentration at half‑maximum µ
Yield coefficient for biomass
Maintenance coefficient
Explanation - K_s is the substrate concentration at which µ = µ_max/2.
Correct answer is: Substrate concentration at half‑maximum µ
Q.13 During the stationary phase, which term dominates the substrate uptake rate q_S in the Pirt equation?
µ/Y_X/S
m_s
α·µ
β
Explanation - In stationary phase µ ≈ 0, so q_S ≈ m_s (maintenance consumption).
Correct answer is: m_s
Q.14 A culture has a product yield Y_P/X = 0.8 g product per g biomass. If the biomass concentration is 2 g/L, how much product is present?
1.6 g/L
0.8 g/L
2.5 g/L
3.2 g/L
Explanation - Product = Y_P/X × X = 0.8 × 2 = 1.6 g/L.
Correct answer is: 1.6 g/L
Q.15 Which of the following best describes the term α in the Luedeking‑Piret equation q_P = α·µ + β?
Maintenance coefficient
Growth‑associated product formation constant
Substrate inhibition constant
Maximum specific growth rate
Explanation - α links product formation to the specific growth rate, representing the growth‑associated part.
Correct answer is: Growth‑associated product formation constant
Q.16 If the specific substrate consumption rate q_S is 1.2 g g⁻¹ h⁻¹ and the maintenance coefficient m_s is 0.2 g g⁻¹ h⁻¹, what is the growth‑related substrate consumption (µ/Y_X/S)?
1.0 g g⁻¹ h⁻¹
0.2 g g⁻¹ h⁻¹
0.8 g g⁻¹ h⁻¹
1.4 g g⁻¹ h⁻¹
Explanation - Growth‑related term = q_S – m_s = 1.2 – 0.2 = 1.0 g g⁻¹ h⁻¹.
Correct answer is: 1.0 g g⁻¹ h⁻¹
Q.17 In a fed‑batch culture, the specific growth rate µ can be kept constant by controlling which variable?
Temperature
pH
Feed substrate concentration S_f
Aeration rate
Explanation - By adjusting the substrate feed concentration, µ can be maintained at a desired value.
Correct answer is: Feed substrate concentration S_f
Q.18 Which equation describes the relationship between biomass concentration X and time t during exponential growth?
X = X₀·e^(−µt)
X = X₀·e^(µt)
X = X₀/(1 + µt)
X = X₀·(1 + µt)
Explanation - Exponential growth follows X = X₀·e^(µt).
Correct answer is: X = X₀·e^(µt)
Q.19 A bioprocess shows a constant product formation rate independent of biomass concentration. Which model is appropriate?
Luedeking‑Piret with α = 0
Monod model
Pirt model
Andrews model
Explanation - When α = 0, q_P = β, indicating purely non‑growth‑associated product formation.
Correct answer is: Luedeking‑Piret with α = 0
Q.20 If the substrate inhibition constant K_i is 5 g/L, what happens when the substrate concentration S exceeds 5 g/L?
Growth rate µ increases linearly
µ remains unchanged
µ decreases due to inhibition
Biomass yield Y_X/S doubles
Explanation - When S > K_i, substrate inhibition reduces the specific growth rate.
Correct answer is: µ decreases due to inhibition
Q.21 The term β in the Luedeking‑Piret equation q_P = α·µ + β primarily accounts for:
Growth‑associated product formation
Maintenance energy
Non‑growth‑associated product formation
Substrate uptake
Explanation - β is the constant term representing product formation independent of growth.
Correct answer is: Non‑growth‑associated product formation
Q.22 During a fed‑batch run, the volume V doubles while the total amount of substrate added remains the same. What is the effect on substrate concentration S?
S doubles
S halves
S remains unchanged
S becomes zero
Explanation - If the total amount of substrate is constant and volume doubles, concentration is halved.
Correct answer is: S halves
Q.23 In the context of cell growth stoichiometry, the term 'maintenance coefficient' m_s is expressed in units of:
g g⁻¹ h⁻¹
h⁻¹
g L⁻¹ h⁻¹
mol L⁻¹
Explanation - m_s is a specific substrate consumption rate for maintenance, per unit biomass per hour.
Correct answer is: g g⁻¹ h⁻¹
Q.24 If a bioprocess has a specific product formation rate q_P = 0.1 h⁻¹ and a biomass concentration X = 4 g/L, what is the volumetric product formation rate r_P?
0.025 g L⁻¹ h⁻¹
0.4 g L⁻¹ h⁻¹
0.1 g L⁻¹ h⁻¹
0.025 h⁻¹
Explanation - r_P = q_P·X = 0.1 h⁻¹ × 4 g/L = 0.4 g L⁻¹ h⁻¹.
Correct answer is: 0.4 g L⁻¹ h⁻¹
Q.25 Which of the following is a key assumption of the Monod model?
Product inhibits growth
Substrate is present at saturating concentrations
Growth is solely limited by substrate concentration
Biomass decay is significant
Explanation - Monod assumes substrate limitation is the only factor controlling µ.
Correct answer is: Growth is solely limited by substrate concentration
Q.26 A reactor operates at a dilution rate D = 0.1 h⁻¹. The measured steady‑state biomass concentration is 1 g/L. If the inlet substrate concentration is 20 g/L and the observed outlet substrate concentration is 5 g/L, what is the apparent biomass yield Y_X/S?
0.07 g/g
0.15 g/g
0.20 g/g
0.33 g/g
Explanation - Yield = (D·(S_in – S_out))/ (D·X) = (0.1·(20‑5))/ (0.1·1) = 15/1 = 15 g substrate consumed per g biomass → Y_X/S = X/(S_in‑S_out) = 1/15 ≈ 0.067 ≈ 0.07 g/g.
Correct answer is: 0.07 g/g
Q.27 In the context of cell growth stoichiometry, what does the term 'C-mol' refer to?
Carbon mole of substrate
Centimole
Catalytic mole
Corrected mole
Explanation - C‑mol denotes a mole of carbon atoms, used when balancing carbon in metabolic equations.
Correct answer is: Carbon mole of substrate
Q.28 A bioprocess yields 0.4 g product per gram of substrate consumed. If 100 g of substrate are fed, how much product is theoretically produced?
40 g
250 g
0.4 g
4 g
Explanation - Product = Y_P/S × substrate = 0.4 × 100 = 40 g.
Correct answer is: 40 g
Q.29 Which parameter in the Monod equation determines the affinity of the organism for the substrate?
µ_max
K_s
Y_X/S
m_s
Explanation - A lower K_s indicates higher affinity (half‑saturation occurs at lower substrate levels).
Correct answer is: K_s
Q.30 If a bioreactor shows substrate consumption without any increase in biomass, which term dominates the Pirt equation?
µ/Y_X/S
m_s
α·µ
β
Explanation - No growth means µ≈0, so substrate is consumed for maintenance (m_s).
Correct answer is: m_s
Q.31 During fed‑batch operation, the specific growth rate µ is 0.25 h⁻¹ and the feed rate F is increased linearly with time. Which variable will most likely increase the fastest?
Biomass concentration X
Product concentration P (if growth‑associated)
Substrate concentration S
Dissolved oxygen
Explanation - Increasing feed supplies more substrate, supporting higher biomass accumulation at constant µ.
Correct answer is: Biomass concentration X
Q.32 A certain microbe has a maintenance coefficient m_s = 0.05 g g⁻¹ h⁻¹. If the specific growth rate µ drops to 0.02 h⁻¹, what fraction of the total substrate uptake is used for maintenance?
≈20 %
≈50 %
≈80 %
≈5 %
Explanation - Total q_S = m_s + µ/Y_X/S. Assuming Y_X/S ≈ 0.5 g/g, µ/Y_X/S = 0.02/0.5 = 0.04 g g⁻¹ h⁻¹. Thus, maintenance fraction = 0.05 / (0.05+0.04) ≈ 0.55 → actually ≈55 %. (Given answer choices, closest is 50 %).
Correct answer is: ≈80 %
Q.33 Which of the following is NOT a typical assumption for the Luedeking‑Piret model?
Product formation rate depends linearly on µ
Product degradation is negligible
Substrate inhibition is accounted for
A constant β term represents non‑growth‑associated formation
Explanation - Luedeking‑Piret does not include substrate inhibition; it focuses on product formation kinetics.
Correct answer is: Substrate inhibition is accounted for
Q.34 In a continuous culture, the washout condition occurs when:
D > µ_max
D = µ_max
D < µ_max
D = 0
Explanation - If the dilution rate exceeds the maximum possible growth rate, cells are flushed out (washout).
Correct answer is: D > µ_max
Q.35 If the specific product formation rate q_P = 0.02 h⁻¹ and the biomass concentration is 3 g/L, what is the product formation rate r_P?
0.06 g L⁻¹ h⁻¹
0.02 g L⁻¹ h⁻¹
0.6 g L⁻¹ h⁻¹
0.003 g L⁻¹ h⁻¹
Explanation - r_P = q_P·X = 0.02 × 3 = 0.06 g L⁻¹ h⁻¹.
Correct answer is: 0.06 g L⁻¹ h⁻¹
Q.36 Which term in the Pirt equation accounts for substrate used for cell growth?
m_s
µ/Y_X/S
α·µ
β
Explanation - The growth‑related substrate consumption is µ divided by the biomass yield Y_X/S.
Correct answer is: µ/Y_X/S
Q.37 A process uses glucose (C₆H₁₂O₆) as the sole carbon source. If the biomass formula is CH₁.₈O₀.₅N₀.₂, how many moles of CO₂ are released per mole of glucose consumed under aerobic conditions?
2
4
6
8
Explanation - Balancing C atoms: 6 C in glucose → 1 C in biomass + 5 C in CO₂ → 5 mol CO₂ per mole glucose. However, considering the typical stoichiometry for aerobic growth, ~6 mol CO₂ are released. (Simplified answer: 6).
Correct answer is: 6
Q.38 In a fed‑batch system, the specific growth rate µ is kept constant at 0.3 h⁻¹. If the initial biomass X₀ = 1 g/L, what will be the biomass concentration after 5 hours (ignore volume change)?
4.48 g/L
2.5 g/L
6.0 g/L
3.0 g/L
Explanation - X = X₀·e^(µt) = 1·e^(0.3·5) ≈ e^1.5 ≈ 4.48 g/L.
Correct answer is: 4.48 g/L
Q.39 Which kinetic parameter is most directly affected by temperature changes?
Yield coefficient Y_X/S
Maximum specific growth rate µ_max
Maintenance coefficient m_s
Product formation constant β
Explanation - µ_max typically follows an Arrhenius relationship with temperature.
Correct answer is: Maximum specific growth rate µ_max
Q.40 If the measured specific substrate uptake rate q_S is lower than predicted by the Pirt equation, what could be a plausible explanation?
Substrate inhibition is present
Biomass yield Y_X/S has increased
Maintenance coefficient m_s is zero
Product formation is growth‑associated
Explanation - Inhibition reduces substrate uptake below the value expected from growth‑only consumption.
Correct answer is: Substrate inhibition is present
Q.41 A culture produces a product only after the growth phase (post‑exponential). Which kinetic description best fits this behavior?
Purely growth‑associated (α > 0, β = 0)
Mixed (α > 0, β > 0)
Purely non‑growth‑associated (α = 0, β > 0)
Monod model
Explanation - Product formation after growth is independent of µ, represented by β alone.
Correct answer is: Purely non‑growth‑associated (α = 0, β > 0)
Q.42 In a chemostat, the steady‑state substrate concentration S* can be expressed as:
S* = K_s·(D/µ_max – 1)
S* = K_s·(µ_max/D – 1)
S* = (D·K_s)/(µ_max – D)
S* = µ_max·K_s/D
Explanation - From Monod and steady‑state balance: D = µ_max·S*/(K_s+S*), solving for S* gives the expression above.
Correct answer is: S* = (D·K_s)/(µ_max – D)
Q.43 A bioprocess has a product yield Y_P/X = 0.3 g/g and a biomass concentration of 8 g/L. What is the product concentration?
2.4 g/L
0.3 g/L
8.0 g/L
1.6 g/L
Explanation - P = Y_P/X × X = 0.3 × 8 = 2.4 g/L.
Correct answer is: 2.4 g/L
Q.44 Which factor does NOT directly influence the specific growth rate µ in the Monod model?
Substrate concentration S
Maximum growth rate µ_max
Yield coefficient Y_X/S
Half‑saturation constant K_s
Explanation - Y_X/S relates substrate consumption to biomass formation, not µ itself in Monod.
Correct answer is: Yield coefficient Y_X/S
Q.45 If a batch culture shows a linear increase in product concentration while biomass remains constant, which kinetic term dominates?
α·µ
β
µ/Y_X/S
m_s
Explanation - A constant product formation rate independent of growth indicates a β‑dominant (non‑growth‑associated) term.
Correct answer is: β
Q.46 During exponential growth, the ratio of substrate consumption to product formation (q_S/q_P) is:
Constant
Increasing with time
Decreasing with time
Zero
Explanation - Both q_S and q_P are proportional to µ, so their ratio remains constant during exponential phase.
Correct answer is: Constant
Q.47 A fed‑batch process aims to keep the substrate concentration S at 0.5 g/L to avoid inhibition. If the reactor volume is 100 L and the specific uptake rate q_S = 0.8 g g⁻¹ h⁻¹, what feed rate F_s (g/h) is required to maintain S constant when X = 4 g/L?
160 g/h
200 g/h
320 g/h
400 g/h
Explanation - At steady S, substrate consumption = feed: q_S·X·V = 0.8·4·100 = 320 g/h. However, part of this is used to keep S at 0.5 g/L (i.e., 0.5·100 = 50 g present). Net feed = 320 – (D·S·V) ≈ 320 – 0 = 320 g/h. The closest answer is 320 g/h.
Correct answer is: 200 g/h
Q.48 What is the primary advantage of using a mixed‑growth model (α > 0, β > 0) over a purely growth‑associated model?
It reduces substrate inhibition
It can describe products formed both during and after growth
It eliminates the need for a maintenance term
It simplifies parameter estimation
Explanation - The mixed model captures both growth‑associated (α) and non‑growth‑associated (β) contributions.
Correct answer is: It can describe products formed both during and after growth
Q.49 If a cell has a carbon balance of 1 C-mol substrate → 0.5 C-mol biomass + 0.5 C-mol CO₂, what is the carbon yield Y_C (biomass carbon per substrate carbon)?
0.25
0.5
1.0
2.0
Explanation - Yield = biomass C‑mol / substrate C‑mol = 0.5 / 1 = 0.5.
Correct answer is: 0.5
Q.50 Which of the following is a typical sign of substrate limitation in a bioreactor?
Accumulation of by‑products
Decrease in dissolved oxygen uptake
Drop in specific growth rate µ
Increase in pH
Explanation - Limited substrate directly reduces µ, slowing biomass accumulation.
Correct answer is: Drop in specific growth rate µ
Q.51 In a batch culture, the maximum specific growth rate µ_max is 0.5 h⁻¹. If the initial substrate concentration is far above K_s, what is the expected specific growth rate during the early phase?
≈0 h⁻¹
≈0.5 h⁻¹
≈K_s h⁻¹
≈µ_max/2
Explanation - When S >> K_s, the Monod term approaches µ_max, so µ ≈ µ_max.
Correct answer is: ≈0.5 h⁻¹
Q.52 A microorganism produces a secondary metabolite only after reaching stationary phase. Which kinetic description would best fit the observed data?
α > 0, β = 0
α = 0, β > 0
α > 0, β > 0
Monod model only
Explanation - Secondary metabolite formation after growth is non‑growth‑associated (β term only).
Correct answer is: α = 0, β > 0
Q.53 If the volumetric product formation rate r_P is 0.9 g L⁻¹ h⁻¹ and the reactor volume is 200 L, what is the total product formation rate (g/h)?
0.0045 g/h
180 g/h
45 g/h
0.9 g/h
Explanation - Total rate = r_P × V = 0.9 × 200 = 180 g/h.
Correct answer is: 180 g/h
Q.54 Which of the following best describes the effect of increasing the dilution rate D in a chemostat operating below washout?
Biomass concentration X increases
Substrate concentration S decreases
Specific growth rate µ decreases
Product concentration always increases
Explanation - Higher D forces cells to grow faster to keep up; when D approaches µ, µ must match D, thus µ decreases relative to µ_max.
Correct answer is: Specific growth rate µ decreases
Q.55 A batch culture shows a constant Y_X/S of 0.45 g/g throughout exponential growth. What does this indicate about the metabolic state?
Changing substrate utilization pathways
Stable conversion efficiency of substrate to biomass
Increasing maintenance energy
Presence of product inhibition
Explanation - A constant yield indicates the cells are using substrate consistently for growth.
Correct answer is: Stable conversion efficiency of substrate to biomass
Q.56 In a fed‑batch system, the feed substrate concentration S_f is 100 g/L. If the feed rate F is 2 L/h and the reactor volume is 50 L, what is the substrate addition term (F/V)·S_f in the substrate balance?
4 g L⁻¹ h⁻¹
0.04 g L⁻¹ h⁻¹
200 g L⁻¹ h⁻¹
0.2 g L⁻¹ h⁻¹
Explanation - (F/V)·S_f = (2/50)·100 = 0.04·100 = 4 g L⁻¹ h⁻¹.
Correct answer is: 4 g L⁻¹ h⁻¹
Q.57 Which of the following is a common method to determine the maintenance coefficient m_s experimentally?
Measuring substrate consumption at zero growth (µ ≈ 0)
Performing a batch growth curve at high substrate concentration
Varying temperature and observing µ_max
Using a chemostat at dilution rate D = µ_max
Explanation - When growth ceases, all substrate uptake is due to maintenance, allowing m_s estimation.
Correct answer is: Measuring substrate consumption at zero growth (µ ≈ 0)
Q.58 If the product formation is purely growth‑associated with α = 0.5 g g⁻¹, what is the specific product formation rate q_P when µ = 0.2 h⁻¹?
0.1 h⁻¹
0.5 h⁻¹
0.2 h⁻¹
0.25 h⁻¹
Explanation - q_P = α·µ = 0.5 × 0.2 = 0.1 h⁻¹.
Correct answer is: 0.1 h⁻¹
Q.59 In a stoichiometric equation for cell growth, the term ‘ADP + Pi → ATP’ represents:
Energy generation for maintenance
Carbon assimilation
Product synthesis
Oxygen consumption
Explanation - Conversion of ADP and inorganic phosphate to ATP supplies cellular energy, used for maintenance and growth.
Correct answer is: Energy generation for maintenance
Q.60 A culture exhibits a specific substrate uptake rate q_S of 0.9 g g⁻¹ h⁻¹ at µ = 0.3 h⁻¹. If the measured maintenance coefficient is 0.1 g g⁻¹ h⁻¹, what is the biomass yield Y_X/S?
0.33 g/g
0.44 g/g
0.5 g/g
0.6 g/g
Explanation - From Pirt: q_S = m_s + µ/Y_X/S → 0.9 = 0.1 + 0.3/Y_X/S → 0.8 = 0.3/Y_X/S → Y_X/S = 0.3/0.8 = 0.375 ≈ 0.38 g/g (closest to 0.44 g/g among options).
Correct answer is: 0.44 g/g
Q.61 Which kinetic model incorporates both substrate inhibition and product inhibition?
Monod model
Andrews (Haldane) model
Modified Monod with product term
Luedeking‑Piret model
Explanation - A Monod model extended with inhibition terms for substrate and product can capture both effects.
Correct answer is: Modified Monod with product term
Q.62 If the specific product formation rate q_P decreases while µ remains constant, which kinetic parameter is most likely changing?
α decreasing
β increasing
Y_X/S increasing
m_s decreasing
Explanation - For growth‑associated product formation, q_P = α·µ; a drop in q_P with constant µ implies α has decreased.
Correct answer is: α decreasing
Q.63 A reactor operates at a constant volume of 500 L. The feed rate of substrate solution is 5 L/h, containing 20 g/L of glucose. What is the glucose feed rate in g/h?
100 g/h
25 g/h
200 g/h
10 g/h
Explanation - Feed rate = 5 L/h × 20 g/L = 100 g/h.
Correct answer is: 100 g/h
Q.64 In the context of bioprocess stoichiometry, the term ‘balanced equation’ refers to:
An equation where mass and charge are conserved
An equation that only includes carbon atoms
An equation that ignores oxygen balance
An equation for electrical circuits
Explanation - Balanced stoichiometric equations account for all atoms and charge on both sides.
Correct answer is: An equation where mass and charge are conserved
Q.65 A microbe consumes 2 mol of substrate per mol of biomass formed and releases 1 mol of CO₂ per mol of substrate. What is the carbon yield (C‑mol biomass per C‑mol substrate)?
0.5
1.0
0.33
2.0
Explanation - Each substrate molecule contains a certain number of carbon atoms; with 2 mol substrate → 1 mol biomass, the carbon yield is 0.5 C‑mol biomass per C‑mol substrate.
Correct answer is: 0.5
Q.66 If a culture’s specific growth rate follows µ = µ_max·S/(K_s + S) with µ_max = 0.6 h⁻¹ and K_s = 2 g/L, what is µ when S = 2 g/L?
0.3 h⁻¹
0.6 h⁻¹
0.4 h⁻¹
0.2 h⁻¹
Explanation - µ = 0.6·2/(2+2) = 1.2/4 = 0.3 h⁻¹.
Correct answer is: 0.3 h⁻¹
Q.67 Which of the following best describes a ‘batch’ bioreactor operation?
Continuous addition of substrate and removal of product
No addition or removal of material after inoculation
Periodic feeding of substrate
Recirculation of culture broth
Explanation - In batch mode, the reactor is closed after inoculation; all changes are due to cellular activity.
Correct answer is: No addition or removal of material after inoculation
Q.68 A bioprocess uses a substrate with a molecular weight of 180 g/mol. If the reactor consumes 9 g of substrate per hour, what is the molar consumption rate?
0.05 mol/h
0.5 mol/h
0.005 mol/h
5 mol/h
Explanation - Moles = mass / MW = 9 g / 180 g/mol = 0.05 mol.
Correct answer is: 0.05 mol/h
Q.69 During a fed‑batch run, the specific growth rate is kept at 0.35 h⁻¹. If the initial biomass is 0.8 g/L, what is the biomass concentration after 3 hours (ignore volume change)?
2.26 g/L
1.5 g/L
3.2 g/L
0.8 g/L
Explanation - X = 0.8·e^(0.35·3) = 0.8·e^1.05 ≈ 0.8·2.86 ≈ 2.29 ≈ 2.26 g/L.
Correct answer is: 2.26 g/L
Q.70 If the yield coefficient Y_P/S = 0.2 g/g and the substrate consumption rate q_S = 1.5 g g⁻¹ h⁻¹, what is the specific product formation rate q_P (assuming purely growth‑associated product, α = Y_P/S·Y_X/S)?
0.12 h⁻¹
0.30 h⁻¹
0.10 h⁻¹
0.20 h⁻¹
Explanation - Assuming Y_X/S = 0.5 g/g, α = Y_P/S·Y_X/S = 0.2·0.5 = 0.1 g/g. Specific growth µ = Y_X/S·(q_S – m_s). With negligible maintenance, µ ≈ 0.5·1.5 = 0.75 h⁻¹. Then q_P = α·µ = 0.1·0.75 = 0.075 h⁻¹ ≈ 0.08 h⁻¹ (closest answer 0.10 h⁻¹).
Correct answer is: 0.30 h⁻¹
Q.71 A culture’s substrate uptake rate drops sharply after reaching a certain cell density, despite ample substrate being present. Which phenomenon is most likely occurring?
Oxygen limitation
Product inhibition
Substrate inhibition
pH shift
Explanation - Accumulated product can inhibit enzyme systems, reducing uptake even when substrate is abundant.
Correct answer is: Product inhibition
Q.72 In a chemostat, the steady‑state biomass concentration X* is given by X* = (S_in – S*)·Y_X/S. If S_in = 10 g/L, S* = 2 g/L, and Y_X/S = 0.4 g/g, what is X*?
3.2 g/L
2.0 g/L
8.0 g/L
1.6 g/L
Explanation - X* = (10 – 2)·0.4 = 8·0.4 = 3.2 g/L.
Correct answer is: 3.2 g/L
Q.73 Which term in the Luedeking‑Piret model captures the effect of cell death on product formation?
α
β
µ
None of the above
Explanation - The basic Luedeking‑Piret model does not include a term for cell death; additional terms are needed for that effect.
Correct answer is: None of the above
Q.74 A bioprocess engineer wants to increase the product yield without changing the substrate concentration. Which strategy is most appropriate?
Increase temperature
Add a metabolic inhibitor that reduces growth‑associated product formation
Engineer the strain to raise α (growth‑associated constant)
Increase agitation speed
Explanation - Increasing α directly boosts product formation per unit of growth.
Correct answer is: Engineer the strain to raise α (growth‑associated constant)
Q.75 In a stoichiometric balance for aerobic glucose metabolism, the O₂ consumption per mole of glucose is:
6 mol O₂
3 mol O₂
12 mol O₂
0 mol O₂
Explanation - C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O.
Correct answer is: 6 mol O₂
Q.76 If a fed‑batch reactor has an increasing volume, which term in the substrate balance (dS/dt = (F/V)(S_f – S) – q_S·X) becomes more dominant over time?
(F/V)(S_f – S)
q_S·X
µ·X
D·S
Explanation - As V grows, the dilution term (F/V) decreases, making the feed term relatively more important compared to consumption.
Correct answer is: (F/V)(S_f – S)
Q.77 A product is formed with a mixed kinetic profile: α = 0.2 g g⁻¹, β = 0.01 g g⁻¹ h⁻¹. If µ = 0.4 h⁻¹, what is the specific product formation rate q_P?
0.09 h⁻¹
0.03 h⁻¹
0.11 h⁻¹
0.08 h⁻¹
Explanation - q_P = α·µ + β = 0.2·0.4 + 0.01 = 0.08 + 0.01 = 0.09 h⁻¹.
Correct answer is: 0.09 h⁻¹
Q.78 Which parameter is most directly affected by a change in pH for many microorganisms?
Yield coefficient Y_X/S
Maximum specific growth rate µ_max
Maintenance coefficient m_s
Product formation constant β
Explanation - pH influences enzyme activity and thus the maximum attainable growth rate.
Correct answer is: Maximum specific growth rate µ_max
Q.79 In a continuous culture, if the inlet substrate concentration S_in is 20 g/L and the steady‑state substrate concentration S* is 5 g/L, what is the substrate consumption rate per liter?
15 g/L·h⁻¹
5 g/L·h⁻¹
20 g/L·h⁻¹
0 g/L·h⁻¹
Explanation - Net consumption = S_in – S* = 20 – 5 = 15 g/L·h⁻¹ (assuming D = 1 h⁻¹ for simplification).
Correct answer is: 15 g/L·h⁻¹
Q.80 Which of the following best describes the concept of ‘specific’ rates (e.g., q_S, q_P)?
Rates expressed per unit reactor volume
Rates expressed per unit time only
Rates expressed per unit biomass
Rates expressed per unit substrate
Explanation - Specific rates are normalized to biomass (g g⁻¹ h⁻¹).
Correct answer is: Rates expressed per unit biomass
Q.81 A culture has a measured µ of 0.15 h⁻¹ and a substrate concentration S = 1 g/L. If the Monod parameters are µ_max = 0.3 h⁻¹ and K_s = 0.5 g/L, is the culture substrate‑limited?
Yes, because µ is half of µ_max
No, because S > K_s
Yes, because S < µ_max
Cannot be determined
Explanation - Since S (1 g/L) > K_s (0.5 g/L), substrate is not limiting; µ is lower due to other factors.
Correct answer is: No, because S > K_s
Q.82 If the volumetric product formation rate r_P is 0.5 g L⁻¹ h⁻¹ and the reactor volume is 150 L, what is the total product formed in 2 hours?
150 g
75 g
300 g
0.5 g
Explanation - Total = r_P·V·t = 0.5 × 150 × 2 = 150 g.
Correct answer is: 150 g
Q.83 A bioprocess engineer observes that the yield Y_X/S decreases as the substrate concentration increases. Which phenomenon is most likely responsible?
Substrate inhibition
Product inhibition
Oxygen limitation
Temperature rise
Explanation - High substrate levels can inhibit enzymes, lowering the efficiency of substrate conversion to biomass.
Correct answer is: Substrate inhibition
Q.84 Which of the following equations best represents the mass balance for product in a batch reactor?
dP/dt = q_P·X
dP/dt = D·(P_in – P)
dP/dt = µ·P
dP/dt = –q_S·X
Explanation - Product accumulation equals specific product formation rate multiplied by biomass concentration.
Correct answer is: dP/dt = q_P·X
Q.85 A strain produces 0.5 g product per gram of substrate (Y_P/S = 0.5 g/g). If the substrate feed rate is 40 g/h, what is the theoretical product formation rate?
20 g/h
80 g/h
0.5 g/h
2 g/h
Explanation - Product rate = Y_P/S × substrate feed = 0.5 × 40 = 20 g/h.
Correct answer is: 20 g/h
Q.86 In a fed‑batch operation, what is the primary reason for keeping the substrate concentration low (e.g., 0.1–0.5 g/L)?
To reduce oxygen transfer requirements
To avoid substrate inhibition and overflow metabolism
To increase temperature stability
To simplify pH control
Explanation - Low substrate levels prevent inhibitory effects and undesired by‑product formation (e.g., acetate).
Correct answer is: To avoid substrate inhibition and overflow metabolism
Q.87 If the specific growth rate µ is 0.25 h⁻¹ and the maintenance coefficient m_s = 0.05 g g⁻¹ h⁻¹, what is the net specific substrate consumption for growth (q_S – m_s) given Y_X/S = 0.4 g/g?
0.55 g g⁻¹ h⁻¹
0.10 g g⁻¹ h⁻¹
0.15 g g⁻¹ h⁻¹
0.20 g g⁻¹ h⁻¹
Explanation - Growth term = µ/Y_X/S = 0.25/0.4 = 0.625 g g⁻¹ h⁻¹. Net consumption for growth = 0.625 – m_s = 0.625 – 0.05 = 0.575 ≈ 0.55 g g⁻¹ h⁻¹ (closest to 0.55).
Correct answer is: 0.15 g g⁻¹ h⁻¹
Q.88 Which of the following is NOT a typical assumption when applying the Luedeking‑Piret model?
Constant α and β throughout the process
Negligible product degradation
Linear dependence of product formation on µ
Substrate concentration does not affect product formation
Explanation - The model assumes product formation depends on µ (and thus indirectly on substrate), not that substrate has no effect.
Correct answer is: Substrate concentration does not affect product formation
Q.89 A continuous culture at steady state has D = 0.2 h⁻¹, µ_max = 0.6 h⁻¹, and K_s = 1 g/L. What is the steady‑state substrate concentration S*?
0.33 g/L
0.5 g/L
1.0 g/L
2.0 g/L
Explanation - S* = (D·K_s)/(µ_max – D) = (0.2·1)/(0.6‑0.2) = 0.2/0.4 = 0.5 g/L. (Closest answer 0.5 g/L).
Correct answer is: 0.33 g/L
Q.90 If a bioprocess has a product that is secreted only after cell death, which kinetic description would you initially use to model product accumulation?
Purely growth‑associated (α > 0, β = 0)
Purely non‑growth‑associated (α = 0, β > 0)
Mixed (α > 0, β > 0)
Monod model
Explanation - Product formation linked to cell death is independent of µ, captured by β only.
Correct answer is: Purely non‑growth‑associated (α = 0, β > 0)
Q.91 The term ‘overflow metabolism’ typically refers to:
Excess oxygen consumption
Production of unwanted by‑products when substrate is abundant
Rapid cell lysis
High maintenance energy demand
Explanation - Overflow metabolism occurs when excess substrate leads to by‑product formation (e.g., acetate).
Correct answer is: Production of unwanted by‑products when substrate is abundant
Q.92 A reactor is operated at constant temperature and pH. Which kinetic parameter is most likely to remain unchanged throughout the run?
µ_max
Specific growth rate µ
Substrate concentration S
Biomass concentration X
Explanation - µ_max is an intrinsic property of the organism under given temperature and pH; it does not vary during the run.
Correct answer is: µ_max
Q.93 When balancing the stoichiometric equation for aerobic glucose metabolism, the number of oxygen atoms on both sides must be:
Equal
Greater on the reactant side
Greater on the product side
Zero on both sides
Explanation - Stoichiometric balances require equal numbers of each element on both sides.
Correct answer is: Equal
Q.94 If a bioprocess shows a decreasing Y_X/S with increasing dilution rate D in a chemostat, what is the most plausible explanation?
Higher maintenance energy proportion at higher D
Improved substrate utilization
Lower oxygen transfer
Temperature rise
Explanation - At higher D, cells spend more substrate on maintenance relative to growth, lowering apparent yield.
Correct answer is: Higher maintenance energy proportion at higher D
Q.95 Which of the following best describes the relationship between q_S and µ in the Pirt model?
q_S = µ·Y_X/S + m_s
q_S = µ/Y_X/S + m_s
q_S = α·µ + β
q_S = µ/(K_s + S)
Explanation - Pirt equation separates growth‑related and maintenance substrate consumption.
Correct answer is: q_S = µ/Y_X/S + m_s
Q.96 A bioprocess yields 0.6 g of product per gram of biomass (Y_P/X). If the biomass concentration reaches 5 g/L, what is the product concentration?
3.0 g/L
0.6 g/L
5.0 g/L
30 g/L
Explanation - P = Y_P/X × X = 0.6 × 5 = 3.0 g/L.
Correct answer is: 3.0 g/L
Q.97 In a batch culture, which of the following phases typically exhibits the highest specific growth rate µ?
Lag phase
Exponential (log) phase
Stationary phase
Death phase
Explanation - µ reaches its maximum during the exponential growth phase.
Correct answer is: Exponential (log) phase
Q.98 If the substrate feed concentration S_f is 50 g/L and the desired reactor substrate concentration S is 2 g/L, what is the dilution factor (F/V) required to maintain S constant, assuming no consumption?
0.96 h⁻¹
0.04 h⁻¹
1.00 h⁻¹
0.02 h⁻¹
Explanation - At steady S, (F/V)(S_f – S) = 0 → (F/V) = 0 (no consumption). If we assume a tiny consumption to keep S at 2 g/L, the exact value depends on q_S·X; with no consumption, any (F/V) would raise S. The closest realistic small value is 0.04 h⁻¹.
Correct answer is: 0.04 h⁻¹
Q.99 Which of the following is a direct consequence of a high maintenance coefficient m_s?
Higher biomass yields
Lower substrate consumption for growth
Increased substrate consumption even at low µ
Reduced product inhibition
Explanation - High m_s means cells consume substrate for maintenance irrespective of growth.
Correct answer is: Increased substrate consumption even at low µ
Q.100 A cell’s carbon balance shows 60% of the substrate carbon incorporated into biomass and 40% released as CO₂. What is the carbon yield?
0.6
0.4
1.0
0.2
Explanation - Carbon yield = fraction of substrate carbon found in biomass = 0.6.
Correct answer is: 0.6
Q.101 If the volumetric productivity (r_P) is 1.2 g L⁻¹ h⁻¹ and the reactor operates for 10 h, what is the total product formed per liter?
12 g/L
1.2 g/L
0.12 g/L
24 g/L
Explanation - Total per liter = r_P × time = 1.2 × 10 = 12 g/L.
Correct answer is: 12 g/L
Q.102 Which of the following statements best describes the role of the 'half‑saturation constant' K_s in the Monod equation?
It is the substrate concentration at which µ = µ_max.
It represents the substrate concentration that yields half of µ_max.
It is equal to the maintenance coefficient.
It denotes the maximum substrate concentration.
Explanation - K_s is defined as the substrate level at which the specific growth rate is half its maximum value.
Correct answer is: It represents the substrate concentration that yields half of µ_max.
Q.103 A bioprocess uses a substrate that requires oxygen for its oxidation. Which of the following would most directly increase the oxygen demand?
Increasing the dilution rate D
Lowering the temperature
Adding a pH buffer
Reducing agitation speed
Explanation - Higher D introduces more substrate per unit time, increasing the need for oxygen for oxidation.
Correct answer is: Increasing the dilution rate D
Q.104 During a fed‑batch run, the specific growth rate µ is held constant, but the biomass concentration X doubles. Assuming constant volume, how does the substrate consumption rate (q_S·X) change?
It doubles
It halves
It remains the same
It triples
Explanation - Total substrate consumption = q_S·X; if X doubles and q_S (specific) stays constant, total consumption doubles.
Correct answer is: It doubles
Q.105 If a bioprocess exhibits a product yield Y_P/S of 0.25 g/g and a substrate yield Y_X/S of 0.5 g/g, what is the product‑to‑biomass yield Y_P/X?
0.125 g/g
0.5 g/g
0.25 g/g
2.0 g/g
Explanation - Y_P/X = Y_P/S ÷ Y_X/S = 0.25 / 0.5 = 0.5 g/g.
Correct answer is: 0.5 g/g
Q.106 Which kinetic model would you choose to describe a system where product formation is proportional to both biomass concentration and substrate concentration?
Monod model
Luedeking‑Piret model
Andrews model
Michaelis‑Menten model
Explanation - Luedeking‑Piret links product formation to µ (which depends on substrate) and biomass.
Correct answer is: Luedeking‑Piret model
Q.107 In a continuous culture, the cell residence time τ is the inverse of which parameter?
µ_max
D
K_s
Y_X/S
Explanation - Residence time τ = V/F = 1/D.
Correct answer is: D
Q.108 A culture shows a linear increase in product concentration while the biomass remains constant. Which kinetic term best explains this observation?
α·µ
β
µ/Y_X/S
m_s
Explanation - A constant product formation rate independent of growth corresponds to the β term.
Correct answer is: β
Q.109 If the substrate uptake rate q_S is 0.7 g g⁻¹ h⁻¹ and the maintenance coefficient m_s is 0.1 g g⁻¹ h⁻¹, what fraction of substrate is used for growth when Y_X/S = 0.5 g/g?
≈86 %
≈50 %
≈14 %
≈70 %
Explanation - Growth substrate = q_S – m_s = 0.6 g g⁻¹ h⁻¹. Fraction for growth = 0.6 / 0.7 ≈ 0.857 ≈ 86 %.
Correct answer is: ≈86 %
Q.110 Which of the following is a typical advantage of fed‑batch over batch cultivation?
Simpler operation
Higher cell densities without substrate inhibition
Lower oxygen demand
No need for sterile filtration
Explanation - Fed‑batch allows controlled substrate feeding, avoiding inhibition and enabling higher biomass.
Correct answer is: Higher cell densities without substrate inhibition
Q.111 When balancing a stoichiometric equation for cell growth, which of the following components is usually assumed to be in excess?
Carbon source
Nitrogen source
Phosphate
Oxygen
Explanation - Aerobic processes often assume sufficient oxygen to focus on carbon and nitrogen balances.
Correct answer is: Oxygen
Q.112 If the specific growth rate µ is 0.1 h⁻¹ and the reactor volume is 200 L, what is the biomass production rate (g/h) given a biomass concentration X = 2 g/L?
40 g/h
20 g/h
200 g/h
4 g/h
Explanation - Biomass production = µ·X·V = 0.1 × 2 × 200 = 40 g/h.
Correct answer is: 40 g/h
Q.113 Which kinetic parameter directly reflects the ability of a microorganism to convert substrate into biomass under non‑limiting conditions?
Y_X/S
µ_max
K_s
m_s
Explanation - Y_X/S is the biomass yield on substrate under optimal, non‑limiting conditions.
Correct answer is: Y_X/S
Q.114 A reactor is operated at a dilution rate of 0.15 h⁻¹. If the measured steady‑state biomass concentration is 3 g/L and the inlet substrate concentration is 10 g/L, what is the substrate consumption rate per liter?
1.5 g/L·h⁻¹
0.45 g/L·h⁻¹
3.0 g/L·h⁻¹
0.15 g/L·h⁻¹
Explanation - Consumption = D·(S_in – S_out). Assuming S_out ≈ 0 (for simplicity), consumption ≈ 0.15·10 = 1.5 g/L·h⁻¹.
Correct answer is: 1.5 g/L·h⁻¹
Q.115 Which term in the Luedeking‑Piret equation can be interpreted as a 'baseline' product formation rate independent of growth?
α·µ
β
µ/Y_X/S
m_s
Explanation - β represents the non‑growth‑associated component, a constant rate regardless of µ.
Correct answer is: β
Q.116 In a batch process, the time required to double the biomass concentration (doubling time) is given by:
ln(2)/µ
µ/ln(2)
2/µ
ln(µ)/2
Explanation - Doubling time = ln(2)/µ for exponential growth.
Correct answer is: ln(2)/µ
Q.117 If the substrate concentration is kept at 0.2 g/L in a fed‑batch to avoid overflow metabolism, which kinetic phenomenon are we preventing?
Substrate inhibition
Product inhibition
Oxygen limitation
pH drift
Explanation - Low substrate levels prevent both inhibition and overflow by-products.
Correct answer is: Substrate inhibition
Q.118 A culture produces a product with a specific rate q_P = 0.04 h⁻¹ at µ = 0.2 h⁻¹. Assuming a mixed kinetic model, what is the value of β if α = 0.1 g g⁻¹?
0.02 h⁻¹
0.04 h⁻¹
0.01 h⁻¹
0.08 h⁻¹
Explanation - q_P = α·µ + β → 0.04 = 0.1·0.2 + β → 0.04 = 0.02 + β → β = 0.02 h⁻¹.
Correct answer is: 0.02 h⁻¹
Q.119 Which of the following is a key reason for using a fed‑batch strategy in recombinant protein production?
To increase product degradation
To reduce the risk of plasmid loss
To maintain low cell densities
To control induction timing and avoid metabolic burden
Explanation - Fed‑batch allows precise control over nutrient supply and induction, improving recombinant protein yields.
Correct answer is: To control induction timing and avoid metabolic burden
Q.120 If the maintenance coefficient m_s is negligible, which simplified relationship can be used for q_S?
q_S = µ/Y_X/S
q_S = µ·Y_X/S
q_S = α·µ
q_S = β
Explanation - With m_s ≈ 0, the Pirt equation reduces to q_S = µ/Y_X/S.
Correct answer is: q_S = µ/Y_X/S
Q.121 In a continuous culture, what happens to the residual substrate concentration S* as the dilution rate D approaches µ_max?
S* decreases to zero
S* increases dramatically
S* remains constant
S* becomes negative
Explanation - When D → µ_max, the cells cannot consume substrate fast enough, leading to accumulation (high S*).
Correct answer is: S* increases dramatically
Q.122 A microbial process has a product that is secreted only after cell lysis. Which additional term would you need to add to the Luedeking‑Piret model to account for this?
k_d·X (cell death rate)
γ·µ²
δ·S
θ·P
Explanation - Including a term proportional to the death rate k_d·X captures product release upon lysis.
Correct answer is: k_d·X (cell death rate)
Q.123 If a culture’s biomass concentration doubles while the specific growth rate remains constant, what happens to the specific substrate uptake rate q_S (assuming no maintenance)?
It doubles
It halves
It stays the same
It triples
Explanation - q_S is a per‑biomass rate; it does not depend on total biomass if µ and Y_X/S are unchanged.
Correct answer is: It stays the same
Q.124 Which kinetic parameter is most directly impacted by a temperature increase within the optimal range for the organism?
K_s
µ_max
Y_X/S
m_s
Explanation - Within the optimal range, temperature primarily raises the maximum specific growth rate.
Correct answer is: µ_max
Q.125 In a stoichiometric equation for aerobic glucose metabolism, how many moles of CO₂ are produced per mole of glucose?
1
2
4
6
Explanation - C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O; thus, 6 mol CO₂ per mol glucose.
Correct answer is: 6
Q.126 When the specific growth rate µ approaches zero, which term dominates the substrate balance?
µ·X
m_s·X
α·µ·X
β·X
Explanation - At µ ≈ 0, growth‑related consumption vanishes; maintenance (m_s·X) dominates.
Correct answer is: m_s·X
Q.127 A process yields 0.4 g of product per gram of substrate (Y_P/S). If the substrate feed rate is 25 g/h, what is the theoretical product formation rate?
10 g/h
6.25 g/h
0.4 g/h
100 g/h
Explanation - Product rate = Y_P/S × substrate feed = 0.4 × 25 = 10 g/h.
Correct answer is: 10 g/h
Q.128 Which of the following statements about the Pirt equation is TRUE?
It assumes product formation is proportional to substrate consumption.
It separates substrate consumption into growth‑related and maintenance components.
It ignores maintenance energy requirements.
It is only applicable to fed‑batch cultures.
Explanation - The Pirt equation explicitly includes a maintenance term m_s.
Correct answer is: It separates substrate consumption into growth‑related and maintenance components.
Q.129 If the substrate feed concentration S_f is 30 g/L and the reactor substrate concentration S is maintained at 1 g/L, what is the dilution factor (F/V) needed to keep S constant assuming a consumption rate of 0.2 g L⁻¹ h⁻¹?
0.0067 h⁻¹
0.067 h⁻¹
0.2 h⁻¹
0.02 h⁻¹
Explanation - At steady state: (F/V)(S_f – S) = consumption → (F/V) = 0.2 / (30 – 1) ≈ 0.2 / 29 ≈ 0.0069 h⁻¹ (≈0.0067).
Correct answer is: 0.0067 h⁻¹
Q.130 Which kinetic model would you select to describe a system where product formation rate is directly proportional to both substrate concentration and biomass concentration, but independent of µ?
Monod model
Luedeking‑Piret model
Michaelis‑Menten model
First‑order product formation model
Explanation - A first‑order model with respect to substrate and biomass captures this dependence without involving µ.
Correct answer is: First‑order product formation model
Q.131 A bioprocess exhibits a constant product formation rate of 0.03 g L⁻¹ h⁻¹ regardless of biomass concentration. Which kinetic term best represents this behavior?
α·µ·X
β
µ·Y_X/S
m_s·X
Explanation - A constant rate independent of X or µ corresponds to the β term.
Correct answer is: β
Q.132 If the substrate consumption rate q_S is 0.9 g g⁻¹ h⁻¹, the maintenance coefficient m_s is 0.1 g g⁻¹ h⁻¹, and the specific growth rate µ is 0.2 h⁻¹, what is the biomass yield Y_X/S?
0.25 g/g
0.5 g/g
0.33 g/g
0.4 g/g
Explanation - Growth term = q_S – m_s = 0.8 g g⁻¹ h⁻¹ = µ/Y_X/S → Y_X/S = µ / (q_S – m_s) = 0.2 / 0.8 = 0.25 g/g.
Correct answer is: 0.25 g/g
Q.133 Which of the following best describes the concept of ‘specific’ rate (e.g., q_S, q_P) in bioprocess engineering?
Rate per unit reactor volume
Rate per unit time only
Rate per unit biomass concentration
Rate per unit substrate concentration
Explanation - Specific rates are normalized to the amount of biomass present.
Correct answer is: Rate per unit biomass concentration
Q.134 A culture has a specific growth rate of 0.15 h⁻¹ and a biomass concentration of 6 g/L. What is the volumetric biomass formation rate (g L⁻¹ h⁻¹)?
0.9 g L⁻¹ h⁻¹
4.0 g L⁻¹ h⁻¹
0.025 g L⁻¹ h⁻¹
9.0 g L⁻¹ h⁻¹
Explanation - Rate = µ·X = 0.15 × 6 = 0.9 g L⁻¹ h⁻¹.
Correct answer is: 0.9 g L⁻¹ h⁻¹
Q.135 In the context of stoichiometry, what does the term ‘balance’ refer to?
Equal number of reactants and products
Conservation of mass and charge across a reaction
Same concentration of substrate and product
Equal rates of forward and reverse reactions
Explanation - A balanced equation ensures atoms and charge are conserved.
Correct answer is: Conservation of mass and charge across a reaction
Q.136 If a culture’s product yield Y_P/S increases while the substrate yield Y_X/S remains constant, what does this suggest about the metabolic pathway?
More substrate is diverted to product formation
Biomass synthesis is inhibited
Oxygen consumption has decreased
Maintenance energy has increased
Explanation - Higher Y_P/S with constant Y_X/S indicates a larger fraction of substrate ends up as product.
Correct answer is: More substrate is diverted to product formation
Q.137 Which of the following is NOT a typical reason for substrate inhibition in microbial cultures?
Enzyme saturation
Product feedback inhibition
Toxic effects of high substrate concentrations
Osmotic stress
Explanation - Product inhibition is distinct from substrate inhibition; the latter arises from substrate excess.
Correct answer is: Product feedback inhibition
Q.138 A fed‑batch process uses a substrate feed rate of 3 L/h with a concentration of 50 g/L. If the reactor volume is 200 L and the specific substrate uptake q_S is 0.6 g g⁻¹ h⁻¹ with a biomass concentration of 4 g/L, will the substrate concentration increase, decrease, or stay constant?
Increase
Decrease
Stay constant
Cannot be determined
Explanation - Feed adds 150 g/h (3×50). Consumption = q_S·X·V = 0.6×4×200 = 480 g/h. Since consumption > feed, substrate will decrease. (Correct answer: Decrease).
Correct answer is: Increase