I85PREP
⌘ K
GATE XL study materials
GATE XL study resources

GATE XL practice questions

One question at a time. Build your GATE XL understanding.

First 50 of 198 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Undergraduate subjects in Engineering/Technology/Architecture

In a batch bioreactor, the specific growth rate of a culture is described by Monod kinetics. If the maximum specific growth rate is 0.4 h⁻¹, the half-saturation constant is 2 g/L, and the substrate concentration is 6 g/L, what is the specific growth rate?

  1. 0.10 h⁻¹
  2. 0.40 h⁻¹
  3. 0.20 h⁻¹
  4. 0.30 h⁻¹ Correct answer.

Explanation

Monod kinetics gives μ = μmax·S/(Ks + S). Substituting 0.4 × 6/(2 + 6) = 0.4 × 0.75 = 0.30 h⁻¹. The rate approaches but never reaches μmax at finite substrate.

Question 2Undergraduate subjects in Engineering/Technology/Architecture

Which type of bioreactor is best described as a stirred tank in which cells are retained by an external separation device and the liquid medium is continuously removed while cells are recycled?

  1. Air-lift reactor
  2. Plug-flow tubular reactor
  3. Fed-batch reactor
  4. Chemostat with cell recycle Correct answer.

Explanation

A chemostat with cell recycle returns biomass from a settler or membrane back to the vessel, decoupling cell residence time from hydraulic residence time. This allows high cell densities at dilution rates above washout.

Question 3Undergraduate subjects in Engineering/Technology/Architecture

In a chemostat operating at steady state, washout of the culture occurs when the dilution rate exceeds which quantity?

  1. The biomass yield coefficient
  2. The maintenance coefficient
  3. The substrate affinity constant
  4. The maximum specific growth rate Correct answer.

Explanation

At steady state the dilution rate equals the specific growth rate. If D exceeds μmax, the cells cannot grow fast enough to replace those leaving, and biomass is washed out.

Question 4Undergraduate subjects in Engineering/Technology/Architecture

Which enzyme class catalyzes the transfer of a phosphate group from ATP to a substrate hydroxyl group?

  1. Hydrolase
  2. Kinase Correct answer.
  3. Oxidoreductase
  4. Ligase

Explanation

Kinases are transferases that move a phosphate group from a high-energy donor such as ATP onto an acceptor molecule. They are central to metabolic regulation and signaling.

Question 5Undergraduate subjects in Engineering/Technology/Architecture

A DNA fragment of 2 kb is to be amplified by PCR. Which component is required to define the boundaries of the amplified region?

  1. A DNA ligase
  2. A pair of sequence-specific primers Correct answer.
  3. A restriction endonuclease
  4. A reverse transcriptase

Explanation

Forward and reverse primers anneal to the flanks of the target and define the sequence that will be copied. Without specific primers, amplification cannot be targeted.

Question 6Undergraduate subjects in Engineering/Technology/Architecture

During the log phase of a batch culture, which relationship correctly describes the change in biomass concentration with time?

  1. Biomass remains constant with time
  2. Biomass decreases exponentially with time
  3. Biomass increases linearly with time
  4. Biomass increases exponentially with time Correct answer.

Explanation

In exponential phase the specific growth rate is constant, so dX/dt = μX, giving X = X0·e^(μt). The growth is therefore exponential rather than linear.

Question 7Undergraduate subjects in Engineering/Technology/Architecture

Which unit operation is most commonly used to remove cells from a fermentation broth on a large scale by centrifugal force?

  1. Centrifugation using a disc-stack separator Correct answer.
  2. Reverse osmosis
  3. Ion exchange
  4. Depth filtration

Explanation

Disc-stack centrifuges generate high centrifugal force and continuous solids discharge, making them suitable for clarifying broths with high cell loads. Filtration is used but is limited by fouling with small cells.

Question 8Undergraduate subjects in Engineering/Technology/Architecture

In a stirred-tank bioreactor, the dimensionless Reynolds number for agitation is used primarily to characterize which property?

  1. Dissolved carbon dioxide concentration
  2. Flow regime around the impeller Correct answer.
  3. Oxygen solubility
  4. Heat sterilization time

Explanation

The impeller Reynolds number compares inertial to viscous forces and determines whether flow is laminar or turbulent. This governs mixing and mass transfer behavior in the vessel.

Question 9Undergraduate subjects in Engineering/Technology/Architecture

A protein is to be purified by ion-exchange chromatography. At pH 7, the protein has a net negative charge. Which resin and elution strategy are most appropriate?

  1. Anion exchange with increasing salt gradient Correct answer.
  2. Anion exchange with decreasing salt gradient
  3. Cation exchange with increasing salt gradient
  4. Cation exchange with decreasing pH gradient

Explanation

A negatively charged protein binds to a positively charged anion-exchange resin at pH 7. Bound protein is eluted by raising the salt concentration, which competes for charged groups.

Question 10Undergraduate subjects in Engineering/Technology/Architecture

In an enzyme-catalyzed reaction following Michaelis–Menten kinetics, the initial rate at a substrate concentration equal to Km is what fraction of Vmax?

  1. One-quarter
  2. Equal to Vmax
  3. One-half Correct answer.
  4. Three-quarters

Explanation

The Michaelis–Menten equation gives v = Vmax·S/(Km + S). When S = Km, the ratio S/(Km + S) equals 0.5, so the rate is half of Vmax.

Question 11Undergraduate subjects in Engineering/Technology/Architecture

A fed-batch culture is used to produce a secondary metabolite. Which feeding strategy most directly avoids overflow metabolism while maintaining high productivity?

  1. Exponential feeding at the maximum specific growth rate
  2. Feedback-controlled feeding based on dissolved oxygen or respiratory quotient Correct answer.
  3. Constant-rate feeding from the start of the run
  4. Pulse feeding of a concentrated substrate solution

Explanation

Feedback control adjusts feed to the culture's actual demand, keeping residual substrate low and preventing overflow metabolism such as acetate accumulation. This balances growth and product formation.

Question 12Undergraduate subjects in Engineering/Technology/Architecture

Which statement correctly describes the role of the oxygen transfer rate (OTR) in aerobic fermentation scale-up?

  1. OTR is determined solely by the solubility of oxygen in water
  2. OTR decreases as the volumetric mass transfer coefficient increases
  3. OTR is independent of impeller speed and sparging rate
  4. OTR must equal or exceed the oxygen uptake rate of the culture Correct answer.

Explanation

For aerobic cultures, oxygen supply must match or exceed demand, so OTR ≥ OUR is required to avoid oxygen limitation. OTR equals kLa multiplied by the concentration driving force.

Question 13Undergraduate subjects in Engineering/Technology/Architecture

In a sterilization process, the Del factor (∇) is used to quantify which aspect of microbial inactivation?

  1. The heat capacity of the medium
  2. The reduction in spore number by a specified factor Correct answer.
  3. The mixing time during heating
  4. The rate of cooling after sterilization

Explanation

The Del factor is the natural logarithm of the ratio of initial to final viable cell number, representing the extent of inactivation. It combines temperature and time through the Arrhenius relationship.

Question 14Undergraduate subjects in Engineering/Technology/Architecture

A plasmid vector carries an ampicillin resistance gene and a lacZ gene with a multiple cloning site. After transformation into a host and plating on ampicillin plus X-gal, which colonies indicate successful insertion of a foreign fragment?

  1. Colonies growing only without ampicillin
  2. Colonies that fail to grow on X-gal plates
  3. White colonies on ampicillin plates Correct answer.
  4. Blue colonies on ampicillin plates

Explanation

Insertion into the lacZ multiple cloning site disrupts β-galactosidase, so the cells cannot cleave X-gal and remain white. Growth on ampicillin confirms that the plasmid was taken up.

Question 15Undergraduate subjects in Engineering/Technology/Architecture

In a mammalian cell culture expressing a therapeutic glycoprotein, which parameter most directly affects the glycosylation profile of the product?

  1. The concentration of glucose in the feed
  2. The impeller tip speed alone
  3. The molecular weight cutoff of the harvest filter
  4. The residence time in the Golgi apparatus, influenced by culture conditions Correct answer.

Explanation

Glycosylation is determined by enzymatic processing in the endoplasmic reticulum and Golgi, which depends on residence time and intracellular conditions. Culture parameters such as pH, dissolved oxygen, and nutrient supply can alter these processing steps.

Question 16Undergraduate subjects in Engineering/Technology/Architecture

Which downstream step is typically performed immediately after cell harvest and before chromatography to remove cells and cell debris?

  1. Affinity chromatography
  2. Primary recovery by centrifugation or microfiltration Correct answer.
  3. Lyophilization
  4. Diafiltration

Explanation

Primary recovery removes cells and debris by centrifugation or microfiltration, protecting subsequent chromatography columns from fouling. Clarified broth is then processed further.

Question 17Undergraduate subjects in Engineering/Technology/Architecture

A bioprocess produces a protein that is sensitive to shear. Which mixer configuration is most suitable for gentle, low-shear mixing in a large vessel?

  1. High-speed Rushton turbine
  2. Anchor impeller at high speed
  3. Marine propeller at low tip speed Correct answer.
  4. Cascading weirs

Explanation

A marine propeller operating at low tip speed provides bulk mixing with low shear stress, reducing damage to shear-sensitive proteins. High-shear impellers are avoided in this application.

Question 18Undergraduate subjects in Engineering/Technology/Architecture

In a two-stage continuous culture, the first stage is used for cell growth and the second for product formation. Which condition in the second stage favors secondary metabolite production?

  1. A growth-limiting nutrient and reduced growth rate Correct answer.
  2. A nutrient-rich medium supporting maximum growth
  3. Complete removal of dissolved oxygen
  4. A dilution rate above the maximum specific growth rate

Explanation

Secondary metabolites are often produced when growth is limited, so a growth-limiting nutrient in the second stage shifts metabolism toward product formation. This decouples growth from production.

Question 19Undergraduate subjects in Engineering/Technology/Architecture

Which type of impeller is most appropriate for gassing a highly viscous non-Newtonian fermentation broth?

  1. Marine propeller
  2. Flat-blade Rushton turbine
  3. Pitched-blade turbine
  4. Large-diameter helical ribbon impeller Correct answer.

Explanation

Helical ribbon impellers provide bulk movement and good mixing in highly viscous, non-Newtonian fluids where standard turbines create caverns. They are widely used in viscous fermentations.

Question 20Undergraduate subjects in Engineering/Technology/Architecture

A protein has an isoelectric point of 5.5. At pH 7.0, which electrophoretic behavior is expected in a standard gel electrophoresis setup?

  1. It does not migrate because it is neutral
  2. It migrates toward the anode because it is negatively charged Correct answer.
  3. It migrates only in the presence of a nonionic detergent
  4. It migrates toward the cathode because it is positively charged

Explanation

At a pH above its pI, a protein carries a net negative charge and therefore migrates toward the positively charged anode. The charge magnitude depends on the difference between pH and pI.

Question 21Undergraduate subjects in Engineering/Technology/Architecture

In a continuous sterilization process, the required holding time is calculated from the Arrhenius equation and the target Del factor. If the temperature is increased while the target Del factor is held constant, what happens to the required holding time?

  1. It remains unchanged
  2. It becomes independent of temperature
  3. It increases proportionally
  4. It decreases exponentially Correct answer.

Explanation

Higher temperature accelerates spore inactivation according to the Arrhenius relationship, so a shorter time achieves the same Del factor. The dependence is exponential in temperature.

Question 22Undergraduate subjects in Engineering/Technology/Architecture

A fed-batch process is controlled to keep the specific growth rate at 0.15 h⁻¹ using exponential feeding. If the initial biomass is 10 g/L and the feed starts at 5 h, what biomass concentration is expected at 9 h, assuming no maintenance and constant yield?

  1. About 13.5 g/L
  2. About 10.0 g/L
  3. About 24.6 g/L
  4. About 18.2 g/L Correct answer.

Explanation

Exponential growth gives X = X0·e^(μΔt), with Δt = 4 h and μ = 0.15 h⁻¹. Thus X = 10 × e^(0.6) ≈ 18.2 g/L.

Question 23Undergraduate subjects in Engineering/Technology/Architecture

A chromatography column shows a reduced plate height of 2.5 at a linear velocity of 0.1 cm/s. If the particle diameter is 100 µm, what is the plate height?

  1. 2.5 mm
  2. 0.4 mm
  3. 0.025 mm
  4. 0.25 mm Correct answer.

Explanation

The plate height equals the reduced plate height multiplied by the particle diameter: H = h·dp = 2.5 × 100 µm = 250 µm = 0.25 mm.

Question 24Undergraduate subjects in Engineering/Technology/Architecture

During scale-up of a stirred bioreactor, constant power per unit volume is maintained. If the impeller diameter is doubled while the impeller speed is adjusted accordingly, how does the volumetric mass transfer coefficient kLa typically change?

  1. It becomes independent of power input
  2. It increases with increasing power input Correct answer.
  3. It remains exactly constant
  4. It decreases sharply

Explanation

Empirical correlations show kLa increases with power input per unit volume, often as kLa ∝ (P/V)^α. Maintaining constant P/V therefore tends to preserve or raise kLa rather than reduce it.

Question 25Undergraduate subjects in Engineering/Technology/Architecture

A recombinant protein is expressed as inclusion bodies in E. coli. Which sequence of steps is most appropriate to obtain active soluble protein?

  1. Harvest, treat with protease, and purify the fragments
  2. Harvest, solubilize with detergent, and directly purify by gel filtration
  3. Harvest, isolate inclusion bodies, solubilize in denaturant, refold, then purify Correct answer.
  4. Harvest, lyse cells, and apply the lysate directly to an affinity column without further treatment

Explanation

Inclusion bodies must be isolated, dissolved in a denaturant such as urea or guanidine, and then refolded to restore activity before purification. Direct purification of insoluble aggregates would not yield active protein.

Question 26Undergraduate subjects in Engineering/Technology/Architecture

In a Lineweaver–Burk plot for an enzyme that shows competitive inhibition, which pair of changes is observed relative to the uninhibited reaction?

  1. The y-intercept is unchanged while the x-intercept moves toward the origin Correct answer.
  2. The y-intercept increases while the x-intercept stays unchanged
  3. Both the y-intercept and x-intercept increase
  4. Both the y-intercept and x-intercept decrease

Explanation

A competitive inhibitor binds only the free enzyme, so the apparent Michaelis constant rises while the maximum velocity is unaltered. On the double-reciprocal plot the y-intercept equals 1/Vmax and therefore stays fixed, whereas the x-intercept equals −1/Km and shifts toward zero as Km increases.

Question 27Undergraduate subjects in Engineering/Technology/Architecture

A bacterial culture has a doubling time of 30 minutes during exponential growth. Starting from 10⁴ cells per mL, what is the approximate cell concentration after 3 hours of unrestricted growth?

  1. 6.4 × 10⁵ cells per mL Correct answer.
  2. 1.28 × 10⁶ cells per mL
  3. 3.2 × 10⁵ cells per mL
  4. 8.0 × 10⁴ cells per mL

Explanation

Three hours contains six doubling periods of 30 minutes each, so the population increases by a factor of 2⁶ = 64. Multiplying 10⁴ by 64 gives 6.4 × 10⁵ cells per mL.

Question 28Undergraduate subjects in Engineering/Technology/Architecture

Which statement correctly describes the role of the KLa value in an aerobic fermentation?

  1. It sets the maximum specific growth rate that the organism can achieve
  2. It determines the stoichiometric yield of biomass per mole of glucose consumed
  3. It measures the rate of carbon dioxide evolution per unit biomass
  4. It quantifies the maximum oxygen supply capability of the reactor, which must exceed the oxygen demand of the culture Correct answer.

Explanation

KLa combines the liquid-side mass transfer coefficient with the interfacial area and defines the highest oxygen transfer rate the vessel can deliver at a given driving force. Successful aerobic operation requires this supply capacity to meet or exceed the oxygen uptake rate demanded by the cells.

Question 29Undergraduate subjects in Engineering/Technology/Architecture

In a chemostat operating at steady state, what happens to the residual substrate concentration when the dilution rate is increased but remains below washout?

  1. It decreases because cells grow faster
  2. It increases because the specific growth rate must rise to match the dilution rate Correct answer.
  3. It becomes zero because substrate is fully consumed
  4. It stays exactly constant regardless of dilution rate

Explanation

At steady state the specific growth rate equals the dilution rate, so a higher dilution rate forces a higher growth rate. Because growth rate depends on substrate through Monod kinetics, the residual substrate concentration must rise to support that faster growth.

Question 30Undergraduate subjects in Engineering/Technology/Architecture

Which membrane separation process is driven primarily by a transmembrane pressure difference and retains dissolved salts while passing water?

  1. Reverse osmosis Correct answer.
  2. Pervaporation
  3. Dialysis
  4. Electrodialysis

Explanation

Reverse osmosis applies pressure above the osmotic pressure to force water through a semipermeable membrane while rejecting dissolved salts. Dialysis and electrodialysis rely on concentration gradients or electric fields respectively, and pervaporation involves evaporative transport of a permeating component.

Question 31Undergraduate subjects in Engineering/Technology/Architecture

A protein mixture is loaded onto a size-exclusion column. Which protein elutes last from the column?

  1. The protein with the highest net positive charge
  2. The protein with the smallest molecular mass Correct answer.
  3. The protein with the highest hydrophobicity
  4. The protein with the largest molecular mass

Explanation

Size-exclusion chromatography separates molecules by their ability to enter the porous beads. Large molecules are excluded from the pores and travel in the void volume, eluting first, while small molecules penetrate the pores and follow a longer path, eluting last.

Question 32Undergraduate subjects in Engineering/Technology/Architecture

Which quantity is used to express the thermal death kinetics of spores in a sterilization calculation?

  1. The partition coefficient
  2. The Reynolds number
  3. The decimal reduction time at a reference temperature Correct answer.
  4. The Michaelis constant

Explanation

The decimal reduction time (D-value) is the time at a specified temperature required to reduce the spore population by one logarithm. Sterilization design uses D-values together with the z-value to compute the required holding time at a given temperature.

Question 33Undergraduate subjects in Engineering/Technology/Architecture

A stirred bioreactor is scaled up while maintaining a constant impeller tip speed. Which parameter is thereby kept approximately constant?

  1. Power input per unit volume
  2. Reynolds number of the impeller
  3. Maximum shear rate at the impeller tip Correct answer.
  4. Mixing time

Explanation

Tip speed equals πND, so holding it constant fixes the maximum linear velocity at the impeller edge and thus the peak shear experienced by cells. This criterion is commonly used when shear-sensitive organisms are involved.

Question 34Undergraduate subjects in Engineering/Technology/Architecture

In a fed-batch culture, which feeding profile maintains a constant specific growth rate during the exponential feeding phase?

  1. Constant feed rate throughout the run
  2. Feed rate proportional to the square root of time
  3. Feed rate increasing exponentially with time Correct answer.
  4. Feed rate decreasing linearly with time

Explanation

To hold the specific growth rate constant, biomass must increase exponentially, so the substrate feed must also rise exponentially to match the growing demand. A constant feed rate would cause the specific growth rate to decline as biomass accumulates.

Question 35Undergraduate subjects in Engineering/Technology/Architecture

Which method is most appropriate for the primary recovery of intracellular recombinant protein from E. coli cells?

  1. Spray drying of the fermentation broth
  2. Ultrafiltration of the whole broth without cell disruption
  3. Affinity chromatography of intact cells
  4. High-pressure homogenization followed by centrifugation Correct answer.

Explanation

Because the product is intracellular, the cells must first be disrupted, and high-pressure homogenization is a standard scalable technique for this. Centrifugation then removes cell debris before further purification.

Question 36Undergraduate subjects in Engineering/Technology/Architecture

Which factor most strongly determines the solubility of a protein in an aqueous buffer near its isoelectric point?

  1. The presence of a high concentration of chaotropic salts
  2. The addition of a non-ionic detergent
  3. The absence of net charge on the protein molecules Correct answer.
  4. The complete unfolding of the protein tertiary structure

Explanation

At the isoelectric point the net charge on the protein is zero, so electrostatic repulsion between molecules is minimized and hydrophobic interactions promote aggregation. This is why proteins generally show minimum solubility at their pI, a principle exploited in isoelectric precipitation.

Question 37Undergraduate subjects in Engineering/Technology/Architecture

Which type of bioreactor is best suited for the large-scale culture of anchorage-dependent mammalian cells?

  1. Bubble column without any solid support
  2. Continuous stirred-tank bioreactor with high shear
  3. Packed-bed bioreactor with porous carriers Correct answer.
  4. Airlift bioreactor with free suspension

Explanation

Anchorage-dependent cells require a solid surface to attach and spread, so packed-bed reactors filled with porous carriers provide a large surface area per unit volume. Suspension-based reactors without support would not sustain attachment-dependent growth.

Question 38Undergraduate subjects in Engineering/Technology/Architecture

Which sterilization approach is preferred for a heat-labile liquid growth medium containing vitamins?

  1. Filtration through a 0.22 µm membrane Correct answer.
  2. Boiling at 100 °C for 30 minutes
  3. Dry heat treatment at 160 °C for 2 hours
  4. Autoclaving at 121 °C for 20 minutes

Explanation

Filtration through a 0.22 µm membrane physically removes microorganisms without exposing heat-labile vitamins to denaturing temperatures. Autoclaving or dry heat would degrade these components.

Question 39Undergraduate subjects in Engineering/Technology/Architecture

In a two-liquid-phase biotransformation, which property of the organic solvent is most critical for maintaining cell viability?

  1. Its refractive index
  2. Its viscosity at low temperature
  3. Its log P value indicating low toxicity to cells Correct answer.
  4. Its boiling point

Explanation

The log P value describes the hydrophobicity of the solvent and correlates with biocompatibility, with values above about 4 generally being least toxic. Solvents with low log P tend to strip lipids from membranes and inactivate cells.

Question 40Undergraduate subjects in Engineering/Technology/Architecture

Which statement about the oxygen uptake rate of a culture is correct when the dissolved oxygen concentration is well above the critical value?

  1. It decreases sharply as the dissolved oxygen concentration rises
  2. It is independent of the dissolved oxygen concentration and set by the metabolic demand Correct answer.
  3. It is limited by the rate of oxygen transfer from the gas phase
  4. It equals the KLa value numerically

Explanation

Above the critical dissolved oxygen level, oxygen is not limiting and the culture respires at its metabolic capacity, so the uptake rate is essentially zero-order with respect to dissolved oxygen. Below that threshold the rate becomes dependent on the available oxygen.

Question 41Undergraduate subjects in Engineering/Technology/Architecture

Which technique separates proteins on the basis of their isoelectric point in an immobilized pH gradient?

  1. Isoelectric focusing Correct answer.
  2. Gel filtration chromatography
  3. SDS-PAGE
  4. Salt precipitation

Explanation

Isoelectric focusing applies an electric field across an immobilized pH gradient, and each protein migrates until it reaches the pH equal to its pI, where its net charge is zero. SDS-PAGE instead separates by molecular mass.

Question 42Undergraduate subjects in Engineering/Technology/Architecture

In an affinity chromatography step using immobilized metal ions, which amino acid residue is most commonly exploited for binding?

  1. Cysteine
  2. Aspartate
  3. Histidine Correct answer.
  4. Leucine

Explanation

Immobilized metal affinity chromatography relies on the coordination of transition metal ions by the imidazole side chain of histidine. Polyhistidine tags are therefore widely used to capture recombinant proteins.

Question 43Undergraduate subjects in Engineering/Technology/Architecture

A batch culture reaches stationary phase. Which explanation best accounts for the cessation of net growth?

  1. The specific growth rate becomes infinite
  2. The cells lose their ribosomes permanently
  3. An essential nutrient is exhausted or inhibitory products accumulate Correct answer.
  4. The medium becomes sterile

Explanation

Stationary phase occurs when growth is balanced by death or when growth stops because a limiting nutrient is depleted or inhibitory metabolites build up. The viable population then remains roughly constant.

Question 44Undergraduate subjects in Engineering/Technology/Architecture

Which parameter of an ion-exchange step is increased to improve resolution between two proteins with similar charge?

  1. The number of theoretical plates in the column Correct answer.
  2. The concentration of the eluting salt in the load
  3. The sample load relative to column capacity
  4. The linear flow rate during loading

Explanation

Resolution improves with the square root of the plate number, so a longer or more efficiently packed column increases theoretical plates and sharpens the separation. Excessive flow or overload instead degrades resolution.

Question 45Undergraduate subjects in Engineering/Technology/Architecture

Which dimensionless group is used to characterize the flow regime in a stirred tank bioreactor?

  1. Nusselt number
  2. Sherwood number
  3. Prandtl number
  4. Impeller Reynolds number Correct answer.

Explanation

The impeller Reynolds number, defined as ρND²/μ, compares inertial to viscous forces in the agitated vessel and determines whether flow is laminar, transitional, or turbulent. Power number correlations depend on this group.

Question 46Undergraduate subjects in Engineering/Technology/Architecture

In a chromatographic separation, the retention factor of a protein is 4. What does this indicate about its migration relative to the mobile phase?

  1. It co-elutes with the solvent front
  2. It is completely excluded from the stationary phase
  3. It moves at one-quarter of the mobile phase velocity Correct answer.
  4. It moves at four times the mobile phase velocity

Explanation

The retention factor k is the ratio of the amount of solute in the stationary phase to that in the mobile phase, and the migration velocity is u/(1+k). With k = 4 the protein travels at one-fifth of the mobile phase velocity, so it is strongly retained.

Question 47Undergraduate subjects in Engineering/Technology/Architecture

Which statement correctly describes the function of a sparger in an aerobic bioreactor?

  1. It removes heat generated by microbial metabolism
  2. It disperses gas into the liquid as bubbles to provide interfacial area for oxygen transfer Correct answer.
  3. It separates cells from the broth during harvest
  4. It sterilizes the incoming air by filtration

Explanation

A sparger introduces air into the liquid and breaks it into bubbles, creating the interfacial area required for oxygen dissolution. Bubble size and distribution strongly influence KLa and thus oxygen supply.

Question 48Undergraduate subjects in Engineering/Technology/Architecture

A protein is to be precipitated from a crude extract by adding ammonium sulfate. Which explanation best describes why the protein precipitates?

  1. The salt binds covalently to the protein surface
  2. The salt denatures the protein irreversibly
  3. The salt competes for water, reducing hydration and exposing hydrophobic patches that aggregate Correct answer.
  4. The salt increases the dielectric constant and strengthens electrostatic repulsion

Explanation

High salt concentrations bind water molecules, reducing the hydration shell around proteins and increasing hydrophobic interactions between them. This salting-out effect causes aggregation and precipitation, and the effect is reversible so the protein can be redissolved.

Question 49Undergraduate subjects in Engineering/Technology/Architecture

Which method would be most suitable for determining the molecular mass of a purified protein under non-denaturing conditions in solution?

  1. SDS-PAGE
  2. Analytical size-exclusion chromatography with suitable standards Correct answer.
  3. Isoelectric focusing
  4. Agarose gel electrophoresis

Explanation

Analytical size-exclusion chromatography elutes proteins according to their hydrodynamic volume, and comparison with standards of known mass provides an estimate under native conditions. SDS-PAGE instead reports the mass of denatured subunits.

Question 50Undergraduate subjects in Engineering/Technology/Architecture

During scale-up of an aerobic fermentation using constant power per unit volume, what typically happens to the dissolved oxygen concentration if the oxygen demand remains unchanged?

  1. It decreases because oxygen transfer capacity per unit volume falls at larger scale Correct answer.
  2. It becomes independent of the KLa value
  3. It remains exactly constant by definition of the criterion
  4. It increases because mixing becomes more efficient

Explanation

Even when power per unit volume is held constant, larger vessels often show lower KLa because of reduced bubble breakup and longer mixing times. With unchanged demand, this reduced transfer capacity can cause dissolved oxygen to fall.