BACE Biotechnician Assistant Credentialing Exam — Questions and Answers

Question 1: How much NaCl (MW = 58.44 g/mol) is needed to prepare 500 mL of a 0.9% (w/v) saline solution?

0.9 g
0.45 g
4.5 g (Correct answer)
9.0 g

Correct answer: 4.5 g

0.9% (w/v) means 0.9 g per 100 mL. For 500 mL: 0.9 g/100 mL x 500 mL = 4.5 g NaCl.

Question 2: What is the OSHA Hazard Communication Standard (HCS) 'Right to Know' law primarily focused on?

Ensuring workers have access to information about hazardous chemicals in the workplace through labels and Safety Data Sheets (Correct answer)
Requiring employers to disclose employee health records to OSHA inspectors
Mandating chemical inventory reporting to federal environmental agencies
Setting maximum permissible exposure limits for all laboratory chemicals

Correct answer: Ensuring workers have access to information about hazardous chemicals in the workplace through labels and Safety Data Sheets

The HCS (29 CFR 1910.1200) requires chemical manufacturers to provide hazard information via labels and SDSs, and employers to train workers on chemical hazards and make SDSs accessible.

Question 3: Which buffer property is most critical to control when performing ion exchange chromatography?

Viscosity and density
Temperature
pH and ionic strength (Correct answer)
Color and turbidity

Correct answer: pH and ionic strength

pH determines the charge state of both the protein and the resin, while ionic strength affects binding strength; both must be tightly controlled for reproducible separations.

Question 4: What does the term 'passage number' refer to in cell culture?

The time elapsed since cells were thawed from cryostorage
The concentration of antibiotics in the media
The number of cells seeded per flask
The number of times cells have been subcultured (split) since the original stock (Correct answer)

Correct answer: The number of times cells have been subcultured (split) since the original stock

Passage number tracks how many times a cell line has been subcultured; high passage numbers can result in genetic drift and altered cell behavior.

Question 5: Why is controlling temperature important during cell culture in a bioreactor?

Because low temperatures increase the dissolved oxygen level in the media
Because temperature controls the pH of the culture broth
Because temperature affects enzyme activity, cell growth rate, product formation, and product quality (Correct answer)
Because high temperatures are needed to keep the media sterile during the run

Correct answer: Because temperature affects enzyme activity, cell growth rate, product formation, and product quality

Temperature directly influences metabolic enzyme kinetics, protein folding, glycosylation patterns, and cell viability, all affecting yield and product quality.

Question 6: In confocal microscopy, what is the primary advantage over conventional fluorescence microscopy?

It provides lower magnification
It requires no fluorescent labels
It eliminates out-of-focus fluorescence to produce sharper optical sections (Correct answer)
It uses visible light instead of laser light

Correct answer: It eliminates out-of-focus fluorescence to produce sharper optical sections

Confocal microscopy uses a pinhole aperture to exclude out-of-focus light, enabling thin optical sectioning and three-dimensional imaging.

Question 7: What is the significance of the melting temperature (Tm) of a PCR primer?

It is the temperature at which 50% of primers are annealed to complementary template used to set the annealing temperature (Correct answer)
It represents the temperature at which the primer denatures from its synthesis oligonucleotide scaffold
It indicates the maximum temperature the PCR machine can heat the sample to
It is the temperature at which DNA polymerase becomes inactive during extension

Correct answer: It is the temperature at which 50% of primers are annealed to complementary template used to set the annealing temperature

Tm is the temperature at which half the primer molecules are annealed to their complementary template; the PCR annealing temperature is typically set 3-5°C below Tm for optimal specificity.

Question 8: Which component of a compound microscope controls the amount of light passing through the specimen?

Condenser
Eyepiece
Iris diaphragm (Correct answer)
Objective lens

Correct answer: Iris diaphragm

The iris diaphragm is an adjustable aperture in the condenser that controls the amount and angle of light illuminating the specimen.

Question 9: A technician prepares a diluted working solution of a hazardous chemical in a spray bottle for daily use. The original stock bottle has a complete GHS label. What is the MINIMUM information required by OSHA on the label for this new 'secondary container'?

The name of the technician who prepared it and the date of preparation.
The full GHS label, including all pictograms and hazard statements.
The chemical identity and words, pictures, or symbols indicating the hazard. (Correct answer)
A piece of tape with the chemical formula written on it.

Correct answer: The chemical identity and words, pictures, or symbols indicating the hazard.

According to OSHA's Hazard Communication Standard, secondary containers must, at a minimum, be labeled with the identity of the hazardous chemical and general information regarding its hazards using words, pictures, or symbols. While a full GHS label is an option, it is not the minimum requirement.

Question 10: What is the correct order of steps when beginning microscopy observation of a new slide?

Place slide → focus with oil immersion objective first → then use dry objectives
Focus without slide → place slide → use highest power immediately
Place slide → use lowest power objective → focus with coarse adjustment → switch to higher power using fine adjustment only (Correct answer)
Place slide → use highest power objective → focus with fine adjustment → switch to lower power

Correct answer: Place slide → use lowest power objective → focus with coarse adjustment → switch to higher power using fine adjustment only

Always start with the lowest power objective to locate the specimen and achieve initial focus before progressing to higher magnification objectives.

Question 11: In SDS-PAGE, what is the primary function of the sodium dodecyl sulfate (SDS) component in the sample loading buffer and the gel running buffer?

To act as a tracking dye to monitor the progress of the electrophoresis.
To denature proteins and impart a uniform negative charge-to-mass ratio. (Correct answer)
To cleave proteins into smaller peptide fragments for better resolution.
To maintain the protein's native three-dimensional structure for activity analysis.

Correct answer: To denature proteins and impart a uniform negative charge-to-mass ratio.

SDS is an anionic detergent that serves two key functions: it disrupts the non-covalent bonds that maintain a protein's secondary and tertiary structure (denaturation), and it coats the linearized protein with a uniform negative charge. This ensures that during electrophoresis, the proteins migrate through the polyacrylamide gel based primarily on their molecular weight, not their intrinsic charge or shape.

Question 12: Which method is commonly used to separate cells from fermentation broth during harvest?

PCR amplification
Centrifugation or depth filtration (Correct answer)
Gel electrophoresis
Ion exchange chromatography

Correct answer: Centrifugation or depth filtration

Centrifugation and depth filtration are primary harvest methods that separate cells (or cell debris) from the broth containing the desired product.

Question 13: What is the significance of the 'specific growth rate' (μ) in fermentation?

It describes how fast cells are growing relative to the existing cell mass at a given moment (Correct answer)
It measures the rate of product formation per unit time
It indicates the rate of pH change in the bioreactor
It quantifies the rate of oxygen consumption by the culture

Correct answer: It describes how fast cells are growing relative to the existing cell mass at a given moment

Specific growth rate (μ, units: h⁻¹) expresses the rate of increase in biomass per unit of existing biomass, defining the exponential growth kinetics.

Question 14: When performing a Bradford assay to create a standard curve, a technician observes that the color of the solution changes from brown to blue upon addition of the protein standards. What is the spectrophotometer measuring at 595 nm?

The rate of reduction of copper ions by the protein.
The absorbance of the protein-dye complex, where the dye has shifted to its blue form. (Correct answer)
The absorbance of the unbound, reddish-brown form of the Coomassie dye.
The intrinsic fluorescence of the protein's tryptophan residues.

Correct answer: The absorbance of the protein-dye complex, where the dye has shifted to its blue form.

The Bradford assay is based on the binding of Coomassie Brilliant Blue G-250 dye to proteins. In its unbound, acidic state, the dye is reddish-brown with an absorbance maximum around 465 nm. When it binds to proteins, it converts to a stable blue form, causing the absorbance maximum to shift to 595 nm. The increase in absorbance at 595 nm is proportional to the amount of protein present.

Question 15: In protein purification, what does 'specific activity' measure, and why does it increase during successful purification?

Specific activity measures the purity of a preparation as a percentage of total protein
Specific activity measures the total enzyme activity in a sample; it decreases during purification as total protein decreases
Specific activity measures enzyme activity per unit total protein (units/mg); it increases during purification as contaminant proteins are removed enriching the target enzyme (Correct answer)
Specific activity is the proportion of active enzyme molecules relative to inactive (denatured) enzyme

Correct answer: Specific activity measures enzyme activity per unit total protein (units/mg); it increases during purification as contaminant proteins are removed enriching the target enzyme

Specific activity = total activity / total protein; as purification removes non-target proteins, total protein decreases while target enzyme activity is maintained, increasing specific activity.

Question 16: What is polyploidy and how does it affect genetic analysis in biotechnology?

Polyploidy is the term for having multiple alleles for a single gene (more than two)
Polyploidy is the condition of having more than two complete sets of chromosomes common in plants and some animals affecting the complexity of genetic analysis (Correct answer)
Polyploidy is a mutation where a single gene is duplicated multiple times within a haploid genome
Polyploidy refers to cells containing multiple copies of a single chromosome (aneuploidy)

Correct answer: Polyploidy is the condition of having more than two complete sets of chromosomes common in plants and some animals affecting the complexity of genetic analysis

Polyploidy (triploid, tetraploid, hexaploid, etc.) means an organism has multiple complete chromosome sets; it is common in crop plants and affects genetic analysis because multiple gene copies complicate genotype-to-phenotype relationships.

Question 17: What is the central dogma of molecular biology?

Protein to DNA to RNA describes the reverse process in eukaryotes
DNA to RNA to Protein describes the flow of genetic information from storage to functional form (Correct answer)
Protein to RNA to DNA describes how proteins direct their own synthesis
RNA to DNA to Protein describes retroviral replication

Correct answer: DNA to RNA to Protein describes the flow of genetic information from storage to functional form

The central dogma states that genetic information flows from DNA (storage) to RNA (transcription) to protein (translation), with replication maintaining the DNA blueprint.

Question 18: How often should the interior surfaces of a biological safety cabinet be decontaminated with 70% ethanol?

Once per week regardless of use
Once per month during scheduled maintenance
Before and after each use session (Correct answer)
Only when visibly soiled

Correct answer: Before and after each use session

BSC interior surfaces should be wiped with 70% ethanol before starting work and again after completing work to ensure the work surface remains free of contamination.

Question 19: What is the primary function of the cell membrane?

To store genetic information for cell division
To synthesize proteins for export
To regulate what enters and exits the cell by acting as a selectively permeable barrier (Correct answer)
To produce energy through oxidative phosphorylation

Correct answer: To regulate what enters and exits the cell by acting as a selectively permeable barrier

The cell membrane is selectively permeable, allowing certain molecules to pass while blocking others, regulating the internal environment of the cell.

Question 20: What does 'void volume' mean in the context of size exclusion chromatography?

The total volume of liquid within the column
The sample volume that can be loaded safely
The volume of buffer needed to equilibrate the column
The volume at which the largest excluded molecules elute (Correct answer)

Correct answer: The volume at which the largest excluded molecules elute

The void volume (V₀) is the volume of mobile phase outside the pores; molecules too large to enter the pores elute at this volume.

Question 21: A laboratory technician notices that a cell culture flask contains turbid (cloudy) media that was previously clear. What is the most likely explanation?

The media pH has shifted due to CO2 levels
The cells have differentiated into a new cell type
The cells are growing normally and have reached confluence
Microbial contamination has occurred in the culture (Correct answer)

Correct answer: Microbial contamination has occurred in the culture

Sudden turbidity in previously clear culture media is a classic sign of microbial (bacterial or yeast) contamination, which rapidly multiplies and clouds the media.

Question 22: What is the function of lysosomes in eukaryotic cells?

To degrade cellular waste, foreign particles, damaged organelles, and macromolecules using acid hydrolases (Correct answer)
To process mRNA transcripts before export to the cytoplasm
To synthesize cholesterol and phospholipids for the cell membrane
To generate metabolic energy through the citric acid cycle

Correct answer: To degrade cellular waste, foreign particles, damaged organelles, and macromolecules using acid hydrolases

Lysosomes are membrane-bound organelles containing acid hydrolases (proteases, lipases, nucleases, glycosidases) that degrade macromolecules delivered by endocytosis or autophagy at acidic pH.

Question 23: What reagent is typically used to elute a protein bound to a Ni-NTA IMAC column?

High salt (e.g., 1 M NaCl)
Low pH buffer (pH 3.0)
Imidazole at high concentration (Correct answer)
Reducing agent such as DTT

Correct answer: Imidazole at high concentration

Imidazole competes with the histidine tag for binding to the Ni²⁺ ion, displacing the His-tagged protein and causing it to elute.

Question 24: What is the purpose of adding sterile water to a lyophilized (freeze-dried) enzyme powder when reconstituting it for laboratory use?

To denature any contaminating proteins present in the lyophilized powder
To lower the pH of the enzyme preparation to the optimal level for activity
To dissolve and hydrate the enzyme restoring its active three-dimensional conformation and activity (Correct answer)
To dilute the enzyme to below the concentration that causes autocatalytic degradation

Correct answer: To dissolve and hydrate the enzyme restoring its active three-dimensional conformation and activity

Lyophilization removes water from biological materials for stable dry storage; reconstitution with sterile water restores the aqueous environment needed for proper protein folding and enzymatic activity.

Question 25: Which of the following activities is a core responsibility of the Quality Assurance (QA) department in a biotechnology company?

Performing identity testing on incoming raw materials.
Executing the steps of a manufacturing process.
Calibrating laboratory analytical balances.
Reviewing and approving Batch Production Records before product release. (Correct answer)

Correct answer: Reviewing and approving Batch Production Records before product release.

Quality Assurance (QA) is responsible for the overall quality system, which includes the final review and approval of all production and control records to ensure cGMP compliance before a product batch is released for distribution. The other tasks are performed by QC (testing), Manufacturing (execution), and either a metrology or QC department (calibration).

Question 26: A protocol requires a 15-minute incubation of an enzymatic reaction at exactly 37°C. Which of the following is the most critical step when using a standard laboratory water bath for this procedure?

Placing the tube in the bath immediately after turning the power on.
Adding a stir bar to the reaction tube to ensure even heating.
Using a lid on the water bath to prevent evaporation.
Ensuring the water level is high enough to cover the portion of the tube containing the reaction mixture. (Correct answer)

Correct answer: Ensuring the water level is high enough to cover the portion of the tube containing the reaction mixture.

For effective and uniform heat transfer, the reaction mixture inside the tube must be fully submerged below the water level in the bath. If the sample liquid is above the water level, it will not be heated to the target temperature, leading to inaccurate results. While using a lid and preheating the bath are good practices, ensuring the sample is submerged is most critical for the incubation itself.

Question 27: What is a bioreactor primarily used for in biotechnology?

To provide a controlled environment for growing microorganisms or cells to produce biological products (Correct answer)
To separate proteins by molecular weight
To store biological samples at low temperatures
To amplify DNA sequences

Correct answer: To provide a controlled environment for growing microorganisms or cells to produce biological products

A bioreactor is a vessel designed to maintain optimal conditions (pH, temperature, oxygen, nutrients) for biological processes such as fermentation or cell culture.

Question 28: A technician needs to sterilize a heat-sensitive liquid solution containing a protein that would be denatured by autoclaving. Which method would be most appropriate for this task?

Autoclaving
Treatment with 70% ethanol
Filtration using a 0.22 µm filter (Correct answer)
Dry heat sterilization

Correct answer: Filtration using a 0.22 µm filter

Filtration is the ideal method for sterilizing heat-sensitive liquids. A filter with a pore size of 0.22 micrometers (µm) is small enough to physically remove most bacteria, but allows the liquid and its dissolved components, like proteins, to pass through without being damaged by heat. Autoclaving and dry heat would destroy the protein. Ethanol is a disinfectant, not a sterilant for solutions.

Question 29: What is the primary purpose of a biosafety cabinet (BSC) in a biotechnology laboratory?

To centrifuge biological samples at high speed
To incubate cell cultures at controlled temperatures
To store hazardous chemicals safely
To provide a sterile work environment and protect personnel from biohazards (Correct answer)

Correct answer: To provide a sterile work environment and protect personnel from biohazards

A biosafety cabinet provides a sterile, HEPA-filtered work area that protects both the samples and the operator from contamination and biohazardous aerosols.

Question 30: A protocol requires a '10x PBS' stock solution. What concentration of NaCl would you expect in the stock, compared to the 1x working solution that contains 137 mM NaCl?

1,370 mM (137 mM x 10) (Correct answer)
274 mM (2x the working concentration)
137 mM (same as working — stocks are not more concentrated)
13.7 mM (one-tenth the working concentration)

Correct answer: 1,370 mM (137 mM x 10)

A 10x stock is 10 times more concentrated than the 1x working solution; 137 mM x 10 = 1,370 mM NaCl in the stock.

Question 31: What type of chemical bond holds the two strands of the DNA double helix together?

Ionic bonds between negatively charged phosphates and positive ions
Covalent phosphodiester bonds
Disulfide bonds between cysteine residues in the DNA structure
Hydrogen bonds between complementary base pairs (Correct answer)

Correct answer: Hydrogen bonds between complementary base pairs

The two DNA strands are held together by hydrogen bonds between complementary base pairs (A-T: 2 hydrogen bonds; G-C: 3 hydrogen bonds).

Question 32: After running a DNA sample on a 1% agarose gel, a technician observes a single, very bright band located very close to the loading well. What is the most likely interpretation of this result?

The incorrect buffer was used to make the gel.
The electrophoresis was run for too long.
The sample contains very small DNA fragments.
The sample contains high molecular weight, undigested genomic DNA. (Correct answer)

Correct answer: The sample contains high molecular weight, undigested genomic DNA.

In agarose gel electrophoresis, larger molecules move more slowly through the gel matrix. A bright band remaining near the well indicates a high concentration of large DNA molecules, such as intact genomic DNA, which have not been fragmented and have struggled to migrate into the gel.

Question 33: A technician observes that a flask of cell culture medium, which was clear and pink the previous day, is now turbid (cloudy) and has turned a distinct yellow color. What is the most likely cause of this change?

The cells have become over-confluent.
Bacterial contamination. (Correct answer)
The CO2 level in the incubator is too low.
Fungal contamination.

Correct answer: Bacterial contamination.

Rapid turbidity (cloudiness) and a sharp drop in pH are classic signs of bacterial contamination. The bacteria grow quickly and produce acidic byproducts, causing the phenol red pH indicator in the medium to change from pink/red to yellow.

Question 34: During agarose gel electrophoresis, what is the primary reason that DNA fragments migrate towards the positive electrode?

Smaller DNA fragments are naturally drawn to a positive pole.
The buffer system creates a pH gradient that attracts the DNA.
The phosphate backbone of DNA carries a strong negative charge. (Correct answer)
The agarose gel matrix is positively charged.

Correct answer: The phosphate backbone of DNA carries a strong negative charge.

DNA has a net negative charge due to the phosphate groups in its sugar-phosphate backbone. When an electric current is applied to the gel, the negatively charged DNA molecules are repelled by the negative electrode (cathode) and attracted to the positive electrode (anode), causing them to migrate through the gel.

Question 35: When dissolving a solute in water, what step should be done first?

Stir the solution
Add water to the final volume
Heat the solution
Weigh the solute (Correct answer)

Correct answer: Weigh the solute

When preparing a solution, the first essential step is to accurately weigh the solute. The amount of solute directly determines the concentration of the final solution. Precise measurement of the solute ensures that the solution will have the desired molarity or percentage concentration, which is critical for experimental accuracy and reproducibility.

Question 36: A biotechnician needs to make 1 L of 50 mM potassium phosphate buffer at pH 6.0 (pKa2 of phosphate = 7.2). Which phosphate salts should be used and what ratio of KH2PO4 to K2HPO4 is needed?

K3PO4 and K2HPO4 in a 1:1 ratio
KH2PO4 and K2HPO4 with approximately 16 parts KH2PO4 to 1 part K2HPO4 (Correct answer)
K2HPO4 and K3PO4 with more K3PO4 than K2HPO4
Only KH2PO4 is needed since pH 6.0 is below pKa2

Correct answer: KH2PO4 and K2HPO4 with approximately 16 parts KH2PO4 to 1 part K2HPO4

Using Henderson-Hasselbalch: 6.0 = 7.2 + log([K2HPO4]/[KH2PO4]), giving [K2HPO4]/[KH2PO4] = 10^(-1.2) = 0.063. So KH2PO4:K2HPO4 ratio is approximately 16:1.

Question 37: Which culture mode continuously adds fresh nutrients while removing spent media at the same rate to maintain a constant volume?

Perfusion culture
Batch culture
Fed-batch culture
Continuous (chemostat) culture (Correct answer)

Correct answer: Continuous (chemostat) culture

In a chemostat, fresh medium is added at a constant rate equal to the outflow rate, maintaining steady-state cell density and nutrient concentration.

Question 38: What is the purpose of a 'lockout/tagout' (LOTO) procedure in a laboratory setting?

To isolate and de-energize hazardous energy sources (electrical, mechanical, thermal) before equipment maintenance to prevent accidental startup (Correct answer)
To secure laboratory notebooks when containing proprietary information
To restrict chemical cabinet access to authorized personnel only
To lock laboratory freezers containing valuable biological samples when staff are absent

Correct answer: To isolate and de-energize hazardous energy sources (electrical, mechanical, thermal) before equipment maintenance to prevent accidental startup

LOTO (OSHA 29 CFR 1910.147) ensures equipment is completely de-energized and cannot start unexpectedly while workers perform maintenance — preventing electrocution, crush injuries, and other energy-related accidents.

Question 39: What is a buffer in chemistry, and why are buffers critical in biotechnology applications?

A buffer is a concentrated salt solution used to prevent protein aggregation
A buffer is a solution that resists changes in pH when small amounts of acid or base are added (Correct answer)
A buffer is any solution used to dissolve biological molecules for storage
A buffer is a solution used to dilute samples before analytical measurements

Correct answer: A buffer is a solution that resists changes in pH when small amounts of acid or base are added

Buffers resist pH changes by containing a weak acid and its conjugate base in equilibrium; they are critical in biotechnology because enzymatic activity, protein stability, and cell viability are highly pH-dependent.

Question 40: A technician is performing size-exclusion chromatography (SEC) to separate a mixture of three proteins with different molecular weights: Protein A (150 kDa), Protein B (75 kDa), and Protein C (25 kDa). In what order will these proteins elute from the column?

The order depends on the charge of the proteins
Protein A, then B, then C (Correct answer)
Protein C, then B, then A
All three proteins will elute at the same time

Correct answer: Protein A, then B, then C

In size-exclusion chromatography, molecules are separated based on their size. The chromatography column is packed with porous beads. Larger molecules, like Protein A (150 kDa), are too big to enter the pores and thus travel around the beads, taking a shorter path and eluting first. Smaller molecules, like Protein C (25 kDa), can enter the pores, taking a longer, more convoluted path through the column, and therefore elute last.

Question 41: What type of electron microscopy is used to examine the internal ultrastructure of thin-sectioned specimens?

Confocal electron microscopy
Fluorescence electron microscopy
Transmission electron microscopy (TEM) (Correct answer)
Scanning electron microscopy (SEM)

Correct answer: Transmission electron microscopy (TEM)

TEM passes electrons through thin specimens to create high-resolution images of internal cellular structures at the nanometer scale.

Question 42: What is the difference between analytical grade and technical grade reagents and when does the distinction matter?

Analytical grade has high purity (>99%) with known low impurity levels; technical grade has lower purity with less specification. The distinction matters for sensitive assays biological applications and when impurities could interfere with results (Correct answer)
Analytical grade is more expensive but only required for expensive downstream applications; technical grade is always sufficient for solution preparation
Analytical grade is required only for HPLC; technical grade is suitable for all other laboratory uses
There is no meaningful chemical difference — both grades are suitable for any laboratory application

Correct answer: Analytical grade has high purity (>99%) with known low impurity levels; technical grade has lower purity with less specification. The distinction matters for sensitive assays biological applications and when impurities could interfere with results

Analytical grade (ACS grade) has purity >99% with specified maximum impurity levels; technical/practical grade has lower purity. The distinction matters critically in sensitive biochemical assays, cell culture, and trace analysis.

Question 43: What is the principle behind ammonium sulfate precipitation for protein purification?

Ammonium sulfate forms covalent crosslinks between adjacent protein molecules causing bulk precipitation
High salt concentrations remove the hydration shell from proteins reducing their solubility until they precipitate (salting out) (Correct answer)
Ammonium sulfate reduces the pH to precipitate proteins at their isoelectric point
Ammonium sulfate chelates metal cofactors causing metalloenzymes to aggregate and precipitate

Correct answer: High salt concentrations remove the hydration shell from proteins reducing their solubility until they precipitate (salting out)

High concentrations of ammonium sulfate compete with proteins for water molecules, removing their hydration shell; without hydration, protein-protein hydrophobic interactions dominate and they precipitate (salting out).

Question 44: What is the 'Global Harmonized System' (GHS) for chemical classification, and what standard documents are associated with it?

A global treaty governing international chemical waste shipment
An international framework harmonizing chemical hazard classification and communication worldwide implemented through standardized Safety Data Sheets and hazard labels (Correct answer)
An international system for classifying chemicals by their potential pharmaceutical applications
A WHO program for regulating laboratory chemical procurement

Correct answer: An international framework harmonizing chemical hazard classification and communication worldwide implemented through standardized Safety Data Sheets and hazard labels

GHS is a UN system providing standardized criteria for classifying chemical hazards and communicating them through uniform SDSs (16 sections) and pictogram-based labels.

Question 45: What does the abbreviation 'GLP' stand for in the context of laboratory equipment use and data recording?

Graduated Liquid Protocol
Government Laboratory Policy
Good Laboratory Practice (Correct answer)
General Laboratory Procedure

Correct answer: Good Laboratory Practice

GLP stands for Good Laboratory Practice — a set of quality principles governing how non-clinical laboratory studies are planned, performed, monitored, recorded, and reported.

Question 46: Which parameter is most critical to monitor during aerobic fermentation in a bioreactor?

Light intensity inside the vessel
Dissolved oxygen (DO) concentration (Correct answer)
Color of the media
Atmospheric pressure outside the bioreactor

Correct answer: Dissolved oxygen (DO) concentration

Dissolved oxygen is critical because aerobic organisms require adequate oxygen for metabolism, and DO depletion can halt growth or shift metabolism.

Question 47: While streaking bacteria on an agar plate using a metal inoculation loop, a technician realizes they forgot to flame the loop after the initial streak. What is the MOST likely outcome of this error?

There will be excessive, confluent growth across the entire plate instead of isolated colonies. (Correct answer)
The agar plate will remain completely sterile with no growth.
The bacteria will fail to grow due to overheating.
Only the initial quadrant of the plate will show bacterial growth.

Correct answer: There will be excessive, confluent growth across the entire plate instead of isolated colonies.

The purpose of flaming the loop between streaking different sections of an agar plate is to dilute the bacteria, reducing the number of cells being spread. By failing to sterilize the loop, the technician carries a high concentration of bacteria into each new section, resulting in heavy, overlapping (confluent) growth instead of the desired well-isolated individual colonies.

Question 48: Which staining technique uses crystal violet and iodine to differentiate bacteria into two groups based on cell wall structure?

Hematoxylin and eosin staining
Giemsa staining
Gram staining (Correct answer)
Acid-fast staining

Correct answer: Gram staining

Gram staining differentiates bacteria into gram-positive (purple) and gram-negative (pink) based on cell wall peptidoglycan content.

Question 49: In thin layer chromatography (TLC), the Rf value is calculated as:

Distance traveled by solvent / distance traveled by spot
Spot intensity / background intensity
Distance traveled by spot / distance traveled by solvent (Correct answer)
Distance from origin to spot / total plate length

Correct answer: Distance traveled by spot / distance traveled by solvent

Rf (retention factor) = distance traveled by the analyte spot ÷ distance traveled by the solvent front, and ranges from 0 to 1.

Question 50: Which of the following is considered a source of chemical contamination in a cell culture, rather than biological contamination?

Mycoplasma
Cross-contamination from another cell line
Yeast spores
Endotoxins from gram-negative bacteria (Correct answer)

Correct answer: Endotoxins from gram-negative bacteria

Endotoxins are lipopolysaccharides from the outer membrane of gram-negative bacteria and are considered chemical contaminants. While they originate from a biological source, they are non-living toxic molecules that can negatively impact cell growth and function. Mycoplasma, yeast, and other cell lines are all living biological contaminants.

Question 51: What is the function of a sparger in a bioreactor?

To remove foam from the surface of the culture
To introduce small bubbles of air or oxygen into the culture medium (Correct answer)
To measure the pH of the fermentation broth
To add nutrients to the bioreactor during fed-batch operation

Correct answer: To introduce small bubbles of air or oxygen into the culture medium

A sparger is a porous device at the bottom of the bioreactor that disperses compressed air or oxygen as fine bubbles to oxygenate the culture.

Question 52: In a eukaryotic cell, where does translation occur after a signal sequence on the ribosome-bound nascent peptide is recognized?

The ribosome moves to the outer mitochondrial membrane for energy-dependent translation
Translation moves to the nucleus where the DNA template is available
The ribosome is directed to the rough endoplasmic reticulum where the peptide is co-translationally inserted into the ER lumen (Correct answer)
Translation pauses until the signal sequence is cleaved then resumes in the cytoplasm

Correct answer: The ribosome is directed to the rough endoplasmic reticulum where the peptide is co-translationally inserted into the ER lumen

Signal sequences on secretory and membrane proteins are recognized by the signal recognition particle (SRP), which targets the ribosome-mRNA complex to the rough ER for co-translational translocation.

Question 53: What does the term 'sterile technique' mean in the context of bioprocessing?

Adding antibiotics to all growth media
Using high-temperature processes to kill all biological agents
Using methods that prevent contamination of cultures by unwanted microorganisms (Correct answer)
Filtering all media through a 0.45-micron filter

Correct answer: Using methods that prevent contamination of cultures by unwanted microorganisms

Sterile technique encompasses all practices used to prevent introduction of contaminants into biological cultures during bioprocessing operations.

Question 54: Which classification of biosafety cabinet is appropriate for working with BSL-3 pathogens?

Class I BSC
Class II Type A1 BSC
Any Class II BSC is sufficient
Class II Type B2 or Class III BSC (Correct answer)

Correct answer: Class II Type B2 or Class III BSC

Class II Type B2 BSCs (100% exhaust) or Class III BSCs (completely enclosed glove boxes) provide the containment required for BSL-3 work.

Question 55: In batch fermentation, when does the 'stationary phase' occur?

When cells are growing at their maximum rate
When cells are first inoculated into fresh media
When nutrient depletion causes the growth rate to equal the death rate, with no net change in cell number (Correct answer)
When the bioreactor is being cleaned between runs

Correct answer: When nutrient depletion causes the growth rate to equal the death rate, with no net change in cell number

The stationary phase occurs after exponential growth when nutrients become limiting and the rate of cell growth equals the rate of cell death.

Question 56: What is 'upstream processing' in bioprocessing?

The purification of the final biological product
Quality control testing of the finished product
All steps involved in growing and harvesting cells or microorganisms, including media preparation and fermentation (Correct answer)
Formulation and packaging of the product

Correct answer: All steps involved in growing and harvesting cells or microorganisms, including media preparation and fermentation

Upstream processing encompasses all steps before product recovery, including strain selection, media preparation, inoculum development, and bioreactor operation.

Question 57: What is the purpose of an autoclave in bioprocessing?

To sterilize media, equipment, and waste using steam under pressure (Correct answer)
To measure pH of growth media
To filter sterile air into the bioreactor
To centrifuge large volumes of culture broth

Correct answer: To sterilize media, equipment, and waste using steam under pressure

An autoclave uses saturated steam at 121°C and 15 psi for typically 15–20 minutes to kill all microorganisms including heat-resistant spores.

Question 58: What is the function of NADH and FADH2 in cellular respiration?

They directly phosphorylate ADP to ATP in the cytoplasm
They are electron carriers that donate electrons to the mitochondrial electron transport chain driving ATP synthesis (Correct answer)
They transport carbon dioxide from cells to the lungs for exhalation
They are cofactors required for glycolysis reactions in the cytoplasm

Correct answer: They are electron carriers that donate electrons to the mitochondrial electron transport chain driving ATP synthesis

NADH and FADH2 are reduced electron carriers that transfer high-energy electrons to the mitochondrial electron transport chain, driving proton pumping and ATP synthesis.

Question 59: What is the purpose of filtering a freshly prepared buffer solution through a 0.22 µm membrane before use in HPLC or cell culture?

To adjust the pH of the buffer to the desired value by removing acidic impurities
To concentrate the buffer by removing water and dissolved gases
To remove any dissolved organic compounds that might interfere with UV detection
To sterilize the buffer and remove particulates that could clog HPLC columns or introduce microbial contamination into cell cultures (Correct answer)

Correct answer: To sterilize the buffer and remove particulates that could clog HPLC columns or introduce microbial contamination into cell cultures

0.22 µm filtration sterilizes the buffer (removes bacteria and fungi) and removes insoluble particles that could cause column back-pressure in HPLC or contaminate cell cultures.

Question 60: What does a Bradford assay (Coomassie Blue dye binding) measure, and what is its color shift?

Total protein concentration; Coomassie Blue shifts from reddish-brown to blue when it binds proteins under acidic conditions (Correct answer)
Lipid concentration; the dye shifts from blue to yellow in the presence of membrane lipids
Total DNA concentration; the dye shifts from blue to clear in the presence of DNA
Enzyme activity; the blue dye is consumed proportional to enzymatic turnover

Correct answer: Total protein concentration; Coomassie Blue shifts from reddish-brown to blue when it binds proteins under acidic conditions

The Bradford assay measures total protein by the color shift of Coomassie Brilliant Blue G-250 from its reddish-brown (free) form to its blue form upon binding to proteins — measured spectrophotometrically at 595 nm.

Question 61: In cGMP, what is a CAPA (Corrective and Preventive Action) system designed to accomplish?

To track equipment maintenance schedules and calibration due dates
To document all employee performance reviews and training records
To address root causes of actual problems (corrective) and potential problems (preventive) to eliminate recurrence (Correct answer)
To manage regulatory filings and submission timelines for new products

Correct answer: To address root causes of actual problems (corrective) and potential problems (preventive) to eliminate recurrence

CAPA addresses quality problems: corrective actions eliminate the root cause of existing non-conformances; preventive actions eliminate potential causes of problems before they occur.

Question 62: What is the purpose of an Environmental Monitoring (EM) program in a cGMP cleanroom?

To track energy consumption for ISO 14001 environmental compliance
To periodically sample air, surfaces, and personnel for microbial and particulate contamination to ensure cleanroom performance (Correct answer)
To monitor chemical vapor levels for OSHA compliance
To measure temperature and humidity for employee comfort

Correct answer: To periodically sample air, surfaces, and personnel for microbial and particulate contamination to ensure cleanroom performance

EM programs sample cleanroom air, surfaces, equipment, and personnel to detect microbial and particle contamination trends and ensure the controlled environment remains within specified limits.

Question 63: A standard operating procedure (SOP) requires preparing a solution of NaOH, 1 N for use in a titration. What does normality (N) mean for NaOH?

Normality is molarity adjusted for temperature; 1 N at 25°C differs from 1 N at 4°C
Normality is the same as molarity for all substances; 1 N NaOH = 1 M NaOH in all contexts
Normality equals molarity times equivalents per mole; for NaOH (1 OH- per formula unit) 1 N = 1 M. For H2SO4 (2 H+ per formula unit) 1 N = 0.5 M (Correct answer)
Normality is a deprecated term not used in modern laboratory practice; always convert to molarity

Correct answer: Normality equals molarity times equivalents per mole; for NaOH (1 OH- per formula unit) 1 N = 1 M. For H2SO4 (2 H+ per formula unit) 1 N = 0.5 M

Normality = molarity x equivalents per mole. For NaOH (provides 1 OH- per molecule), 1 N = 1 M. For sulfuric acid (provides 2 H+ per molecule), 1 N = 0.5 M.

Question 64: What is 'scale-up' in bioprocessing?

Increasing the production volume from small laboratory bioreactors to large industrial-scale fermenters (Correct answer)
Increasing the concentration of nutrients in the growth medium
Increasing the number of cell passages before production
Increasing the speed of centrifugation to improve yield

Correct answer: Increasing the production volume from small laboratory bioreactors to large industrial-scale fermenters

Scale-up involves transitioning processes from bench-scale (liters) to pilot scale and then to manufacturing scale (thousands of liters) while maintaining product quality.

Question 65: What is the primary unit of concentration for solutions in a laboratory?

Mole per liter (Molarity, M) (Correct answer)
Parts per million (ppm)
Grams per liter (g/L)
Milligrams (mg)

Correct answer: Mole per liter (Molarity, M)

Molarity (M), defined as moles of solute per liter of solution, is the primary unit of concentration used in laboratory settings. It provides a precise measure of the number of solute particles in a given volume, which is crucial for chemical reactions and stoichiometric calculations. This unit allows for accurate and reproducible preparation of solutions for various experiments and analyses.

Question 66: Which type of microscopy is best suited for creating three-dimensional reconstructions of thick fluorescent specimens?

Confocal laser scanning microscopy (Correct answer)
Bright-field microscopy
Dark-field microscopy
Simple light microscopy

Correct answer: Confocal laser scanning microscopy

Confocal microscopy acquires serial optical sections through the specimen that can be digitally stacked to reconstruct three-dimensional structures.

Question 67: Which type of balance should be used when accurately weighing 50 mg of a reagent for a critical buffer preparation?

An analytical balance with 0.0001 g (0.1 mg) readability (Correct answer)
A triple beam balance
A top-loading balance with 0.1 g readability
A platform scale with 1 g readability

Correct answer: An analytical balance with 0.0001 g (0.1 mg) readability

An analytical balance with 0.1 mg readability provides the precision needed for accurately measuring small quantities like 50 mg.

Question 68: When preparing a 1 M phosphate buffer at pH 7.2 using KH2PO4 and K2HPO4, what ratio of K2HPO4 to KH2PO4 is required? (pKa2 of phosphate = 7.2)

Approximately 1:10 (mostly KH2PO4)
Approximately 1:1 (equal amounts of both salts) (Correct answer)
Approximately 10:1 (mostly K2HPO4)
Only K2HPO4 is needed, no KH2PO4

Correct answer: Approximately 1:1 (equal amounts of both salts)

At pH = pKa2 = 7.2, the Henderson-Hasselbalch equation gives log([K2HPO4]/[KH2PO4]) = 0, so ratio = 1. Equal moles of K2HPO4 and KH2PO4 needed.

Question 69: What is the primary purpose of a 'Site Master File' (SMF) in pharmaceutical cGMP?

It provides financial accountability for all manufacturing costs
It is the internal quality manual used for employee training
It is a comprehensive document describing a facility's GMP operations submitted to regulatory authorities to facilitate drug product approval (Correct answer)
It is the regulatory license required before any manufacturing can begin

Correct answer: It is a comprehensive document describing a facility's GMP operations submitted to regulatory authorities to facilitate drug product approval

A Site Master File provides regulatory authorities with a comprehensive description of a manufacturing facility's GMP systems, processes, and controls to support regulatory review.

Question 70: In fluorescence microscopy, what does a fluorophore do when excited by light of the correct wavelength?

It generates heat to warm the specimen
It absorbs all wavelengths of light equally
It reflects the excitation light back to the detector
It absorbs the excitation light and emits light at a longer wavelength (Correct answer)

Correct answer: It absorbs the excitation light and emits light at a longer wavelength

A fluorophore absorbs photons at its excitation wavelength and re-emits photons at a longer (lower energy) emission wavelength, a process called fluorescence.

Question 71: Which organelle is responsible for producing ATP through cellular respiration in eukaryotic cells?

Endoplasmic reticulum
Mitochondria (Correct answer)
Nucleus
Ribosome

Correct answer: Mitochondria

Mitochondria carry out oxidative phosphorylation, producing the majority of ATP used by eukaryotic cells through the electron transport chain.

Question 72: What is the Henderson-Hasselbalch equation used for in laboratory buffer preparation?

Determining the rate of enzyme-catalyzed reactions in buffered solutions
Calculating the ratio of conjugate acid to base needed to achieve a target pH, or predicting pH from the ratio of buffer components present (Correct answer)
Calculating the molarity of a buffer from its weight/volume percentage
Calculating the osmolarity of a buffer solution based on its ionic composition

Correct answer: Calculating the ratio of conjugate acid to base needed to achieve a target pH, or predicting pH from the ratio of buffer components present

The Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])) relates pH to the ratio of conjugate base to acid, allowing calculation of required ratios to achieve a target pH.

Question 73: Why must you never use a mercury thermometer in a laboratory incubator or water bath?

Mercury expands too quickly causing inaccurate readings at higher temperatures
If broken, mercury vapor and liquid mercury create serious health and environmental hazards that are difficult to remediate (Correct answer)
Mercury reacts with CO2 used in cell culture incubators
Mercury thermometers cannot measure temperatures above 37°C

Correct answer: If broken, mercury vapor and liquid mercury create serious health and environmental hazards that are difficult to remediate

Mercury is a potent neurotoxin; breakage releases mercury vapor and liquid mercury requiring specialized, costly cleanup and posing serious health risks to laboratory staff.

Question 74: What does BSL-2 (Biosafety Level 2) designation mean for a laboratory agent?

The agent is non-hazardous and requires only basic containment measures
The agent poses extreme risk of transmission and requires maximum containment
The agent is safe for work on standard benches with no special precautions
The agent poses moderate hazard to personnel and environment; risk groups include human pathogens causing non-severe disease with available treatment (Correct answer)

Correct answer: The agent poses moderate hazard to personnel and environment; risk groups include human pathogens causing non-severe disease with available treatment

BSL-2 agents present moderate hazard to personnel and environment and include organisms like Salmonella and hepatitis B virus; standard precautions plus BSC use and limited access are required.

Question 75: A buffer protocol requires 'Tris-HCl pH 8.0'. What does this notation specifically indicate about how the buffer was prepared?

Tris base was partially protonated by adding HCl until pH 8.0 was reached, creating a mixture of Tris base and Tris-HCl (the conjugate acid) (Correct answer)
Only Tris base was used and the final pH happened to be 8.0
Tris was purchased as the pre-made HCl salt and dissolved to pH 8.0 without adjustment
HCl was added to a Tris solution to lower pH to 8.0 using only 0.1 M HCl

Correct answer: Tris base was partially protonated by adding HCl until pH 8.0 was reached, creating a mixture of Tris base and Tris-HCl (the conjugate acid)

Tris-HCl pH 8.0 means Tris base was dissolved in water and HCl was added to titrate some base to its conjugate acid form (Tris-H+), establishing the buffer at pH 8.0.

Question 76: What type of eye protection is required when working with potentially infectious biological materials or chemical splashes?

Wraparound safety glasses without chemical splash protection
Standard prescription eyeglasses provide adequate eye protection
Chemical splash goggles or a face shield worn over safety glasses (Correct answer)
UV-blocking sunglasses rated for laboratory use

Correct answer: Chemical splash goggles or a face shield worn over safety glasses

Chemical splash goggles seal around the eyes and protect against liquid splashes; standard safety glasses alone do not prevent liquid from entering above, below, or beside the lens.

Question 77: In SDS-PAGE, why are proteins separated primarily by molecular weight?

Reducing agents in the sample buffer separate proteins by charge while SDS separates by size
SDS binds uniformly to proteins (approximately 1.4 g SDS per g protein), giving all proteins a uniform negative charge-to-mass ratio so that migration depends only on molecular size (Correct answer)
The polyacrylamide gel selectively binds large proteins retarding their migration based on charge density
SDS gives each protein a unique net charge proportional to its amino acid composition

Correct answer: SDS binds uniformly to proteins (approximately 1.4 g SDS per g protein), giving all proteins a uniform negative charge-to-mass ratio so that migration depends only on molecular size

SDS binds proteins at approximately 1.4 g/g, coating them with negative charges proportional to their mass, so all proteins migrate with the same charge-to-mass ratio and are separated only by the sieving effect of the polyacrylamide gel.

Question 78: Which of the following is a key principle of aseptic technique designed to maintain the sterility of a work area and culture?

Pouring media directly from large stock bottles to avoid pipetting errors.
Keeping sterile items and cultures open to the air as briefly as possible. (Correct answer)
Working quickly to minimize the time for contamination.
Using antibiotics in all media to prevent any bacterial growth.

Correct answer: Keeping sterile items and cultures open to the air as briefly as possible.

A core principle of aseptic technique is to minimize the exposure of sterile materials to the non-sterile environment. This includes keeping lids on petri dishes, capping tubes and flasks promptly, and generally reducing the time that sterile surfaces are open to the air where airborne contaminants can settle.

Question 79: What is the function of the condenser in a compound light microscope?

To magnify the final image seen by the observer
To focus light onto the specimen to maximize illumination and resolution (Correct answer)
To adjust the magnification of the eyepiece
To hold the objective lenses in position

Correct answer: To focus light onto the specimen to maximize illumination and resolution

The condenser focuses light from the illuminator onto the specimen, optimizing the cone of light for the objective lens being used.

Question 80: After an affinity chromatography purification step, the column is often regenerated by:

Autoclaving the column at 121°C
Storing it dry at room temperature
Flushing with a regeneration solution to remove residual bound material, then re-equilibrating (Correct answer)
Reversing the flow direction permanently

Correct answer: Flushing with a regeneration solution to remove residual bound material, then re-equilibrating

Regeneration involves washing away any remaining bound material with an appropriate stripping solution, followed by re-equilibration in storage or binding buffer to restore column capacity.

Question 81: Under OSHA 29 CFR 1910.1450 (Occupational Exposure to Hazardous Chemicals in Laboratories), what document is required in every academic or research laboratory?

An annual employee health surveillance report submitted to OSHA
A written Chemical Hygiene Plan (CHP) describing procedures and controls for chemical safety (Correct answer)
A written Emergency Action Plan (EAP) filed with the local fire department
A complete inventory of all chemical quantities submitted to the EPA

Correct answer: A written Chemical Hygiene Plan (CHP) describing procedures and controls for chemical safety

29 CFR 1910.1450 requires laboratories to have a written Chemical Hygiene Plan (CHP) that outlines procedures, equipment, PPE, and work practices to protect employees from hazardous chemical exposures.

Question 82: A biotechnician needs to purify a large batch of a recombinant protein that has been engineered to include a polyhistidine tag (His-tag). Which type of chromatography would be the MOST effective and specific method for this initial capture step?

Immobilized Metal Affinity Chromatography (IMAC) (Correct answer)
Anion Exchange Chromatography
Hydrophobic Interaction Chromatography
Size-Exclusion Chromatography

Correct answer: Immobilized Metal Affinity Chromatography (IMAC)

Immobilized Metal Affinity Chromatography (IMAC) is the most specific and effective method for purifying His-tagged proteins. The resin in the column is chelated with divalent metal ions (like Nickel or Cobalt) that have a high affinity for the series of histidine residues on the tag, allowing the target protein to bind tightly while most other cellular proteins wash through.

Question 83: What is CRISPR-Cas9 and how does it function as a genome editing tool?

CRISPR-Cas9 is a recombination system that inserts foreign DNA into bacterial chromosomes for cloning
CRISPR-Cas9 is a restriction enzyme system that cuts DNA at palindromic recognition sequences
CRISPR-Cas9 is a PCR-based technique for amplifying specific genomic sequences
CRISPR-Cas9 is a bacterial immune system repurposed for genome editing — a guide RNA directs Cas9 nuclease to a specific DNA sequence where it makes a double-strand break (Correct answer)

Correct answer: CRISPR-Cas9 is a bacterial immune system repurposed for genome editing — a guide RNA directs Cas9 nuclease to a specific DNA sequence where it makes a double-strand break

CRISPR-Cas9 uses a guide RNA (gRNA) complementary to the target DNA sequence to direct the Cas9 endonuclease to make a precise double-strand break, enabling gene knockout, correction, or insertion.

Question 84: A lab needs to accurately quantify the total protein concentration in crude cell lysates that contain a high concentration of detergents, such as Triton X-100. Which of the following quantification methods is generally more suitable and less prone to interference from these detergents?

Bicinchoninic acid (BCA) assay (Correct answer)
Direct A280 absorbance
Bradford assay
SDS-PAGE with densitometry

Correct answer: Bicinchoninic acid (BCA) assay

The BCA assay is known for its compatibility with samples containing detergents up to 5%. Its chemistry, involving the reduction of copper ions, is less affected by common non-ionic and ionic detergents found in cell lysis buffers compared to the Bradford assay, which can show significant interference as detergents disrupt the dye-protein binding mechanism.

Question 85: When using a spectrophotometer to measure the absorbance of a colored solution, what is the primary purpose of first inserting a 'blank' cuvette containing only the solvent?

To set the maximum absorbance reading (100%) for the instrument.
To calibrate the instrument by setting the absorbance of the solvent to zero. (Correct answer)
To verify that the correct wavelength has been selected.
To clean the optical pathway of the instrument before the real measurement.

Correct answer: To calibrate the instrument by setting the absorbance of the solvent to zero.

The purpose of a blank is to zero the spectrophotometer. The blank contains all components of the sample except for the analyte being measured. By setting the absorbance of the blank to zero, the instrument subtracts any absorbance caused by the solvent or the cuvette itself, ensuring that the final reading reflects only the absorbance of the analyte.

Question 86: What does "q.s." mean when preparing a solution?

Quantify the solute
Add sufficient quantity of solvent (Correct answer)
Heat to dissolve
Add more solute

Correct answer: Add sufficient quantity of solvent

In solution preparation, 'q.s.' stands for 'quantum sufficit,' which is Latin for 'as much as suffices' or 'sufficient quantity.' This instruction means to add enough solvent to reach the final desired volume of the solution. It ensures that the solute is fully dissolved and the solution's concentration is accurately established by bringing it to a precise final volume.

Question 87: A biotechnician is asked to make a 1:10 dilution of a concentrated stock solution to a final volume of 100 mL. Which of the following correctly describes the procedure?

Mix 90 mL of stock solution with 10 mL of diluent.
Mix 10 mL of stock solution with 100 mL of diluent.
Mix 10 mL of stock solution with 90 mL of diluent. (Correct answer)
Mix 1 mL of stock solution with 99 mL of diluent.

Correct answer: Mix 10 mL of stock solution with 90 mL of diluent.

A 1:10 dilution means 1 part of the stock solution is mixed with 9 parts of the diluent for a total of 10 parts. To get a final volume of 100 mL, you would divide the total volume by the total number of parts (100 mL / 10 parts = 10 mL/part). Therefore, you need 1 part stock (10 mL) and 9 parts diluent (90 mL).

Question 88: A technician needs to prepare 500 mL of a 0.5 M Tris-HCl buffer. The formula weight of Tris is 121.14 g/mol. How many grams of Tris should be weighed out?

500 g
30.29 g (Correct answer)
60.57 g
121.14 g

Correct answer: 30.29 g

To calculate the mass of solute needed, use the formula: Mass (g) = Molarity (mol/L) x Volume (L) x Formula Weight (g/mol). First, convert the volume from mL to L: 500 mL = 0.5 L. Then, plug in the values: Mass (g) = 0.5 mol/L x 0.5 L x 121.14 g/mol = 30.285 g, which is rounded to 30.29 g.

Question 89: In biochemistry, what is competitive inhibition of an enzyme?

A molecule permanently inactivates the enzyme by covalently modifying the active site
A molecule binds an allosteric site and changes enzyme conformation to reduce activity regardless of substrate concentration
A molecule binds covalently to the active site only when substrate is also bound
A molecule that resembles the substrate competes for binding at the active site reducing enzymatic activity but can be overcome by increasing substrate concentration (Correct answer)

Correct answer: A molecule that resembles the substrate competes for binding at the active site reducing enzymatic activity but can be overcome by increasing substrate concentration

A competitive inhibitor structurally resembles the substrate and competes for the active site; increasing substrate concentration outcompetes the inhibitor, restoring Vmax while Km appears increased.

Question 90: What does the 'c' in 'cGMP' stand for, and why is it significant?

'Certified' indicating the facility has passed FDA inspection
'Comprehensive' indicating all aspects of manufacturing are covered
'Compliant' indicating the manufacturer follows all applicable laws
'Current' indicating regulations reflect state-of-the-art technology and are updated as science advances (Correct answer)

Correct answer: 'Current' indicating regulations reflect state-of-the-art technology and are updated as science advances

'Current' signifies that GMP standards evolve with technological advances — manufacturers must adopt the most up-to-date practices, not just meet historical minimum standards.

Question 91: What technique separates proteins based on their isoelectric point (pI)?

Hydrophobic interaction chromatography
Ion exchange chromatography
Gel filtration chromatography
Isoelectric focusing (IEF) (Correct answer)

Correct answer: Isoelectric focusing (IEF)

Isoelectric focusing applies a pH gradient to a gel or capillary; proteins migrate until they reach the pH region equal to their pI, where they carry no net charge and stop migrating.

Question 92: A technician prepares a solution by dissolving 58.44 grams of NaCl (Formula Weight = 58.44 g/mol) in enough water to make a final volume of 1.0 L. What is the molarity (M) of this solution?

2.0 M
0.5 M
1.0 M (Correct answer)
0.1 M

Correct answer: 1.0 M

Molarity is defined as moles of solute per liter of solution. First, calculate the number of moles of NaCl: Moles = Mass (g) / Formula Weight (g/mol) = 58.44 g / 58.44 g/mol = 1.0 mole. Since the final volume is 1.0 L, the molarity is 1.0 mole / 1.0 L = 1.0 M.

Question 93: A 100x antibiotic stock solution must be prepared for cell culture use. If the working concentration of penicillin is 100 U/mL, how many units of penicillin are in 1 mL of the 100x stock?

100,000 U
1,000 U
100 U
10,000 U (Correct answer)

Correct answer: 10,000 U

A 100x stock is 100 times more concentrated than the working solution. Working = 100 U/mL x 100-fold = 10,000 U/mL in the stock.

Question 94: When splitting (passaging) adherent cells, trypsin is added after washing with PBS. What is the purpose of the PBS wash?

To remove serum proteins that would inhibit trypsin activity (Correct answer)
To activate the trypsin enzyme before it contacts cells
To lower media pH to enhance trypsin efficiency
To provide nutrients to cells during the trypsin treatment

Correct answer: To remove serum proteins that would inhibit trypsin activity

FBS/serum in the culture media contains trypsin inhibitors (alpha-2-macroglobulin and alpha-1-antitrypsin); washing with PBS removes these inhibitors before adding trypsin.

Question 95: What is the primary function of providing a 5% CO2 atmosphere in a standard mammalian cell culture incubator?

To provide a direct carbon source for cell metabolism.
To work with the bicarbonate buffer system in the medium to maintain a stable pH. (Correct answer)
To increase the dissolved oxygen levels in the culture medium.
To prevent anaerobic bacteria from growing.

Correct answer: To work with the bicarbonate buffer system in the medium to maintain a stable pH.

The CO2 gas in the incubator dissolves in the cell culture medium and forms a bicarbonate buffer system. This system is crucial for maintaining a stable, physiological pH (typically around 7.2-7.4), which is essential for cell viability and growth.

Question 96: Before starting a microcentrifuge, a technician places two 1.5 mL tubes containing samples of unequal mass opposite each other in the rotor. What is the most likely consequence of this action?

The samples will not pellet correctly.
The centrifuge lid will not lock properly.
The run time will automatically increase to compensate.
The centrifuge will generate excessive noise and vibration, potentially damaging the unit. (Correct answer)

Correct answer: The centrifuge will generate excessive noise and vibration, potentially damaging the unit.

Centrifuges must be properly balanced by mass to operate safely and effectively. Placing tubes with unequal masses opposite each other creates an imbalance. At high rotational speeds, this imbalance causes significant vibration, which can damage the motor and rotor, posing a serious safety risk.

Question 97: What is the volume of water needed to prepare a 1 M NaCl solution using 58.44 g of NaCl?

1 L (Correct answer)
0.5 L
5 L
2 L

Correct answer: 1 L

To prepare a 1 M NaCl solution using 58.44 g of NaCl, you need to understand the definition of molarity. The molar mass of NaCl is approximately 58.44 g/mol, meaning 58.44 g constitutes 1 mole of NaCl. A 1 M solution contains 1 mole of solute per liter of solution, so dissolving 58.44 g of NaCl and bringing the total volume to 1 L with water will yield a 1 M solution.

Question 98: When working with cell cultures in a Class II Biological Safety Cabinet (BSC), which of the following is a critical aseptic technique to prevent contamination?

Keeping the UV light on while working to sterilize the air.
Wearing two pairs of gloves for extra protection.
Moving hands and arms rapidly to create a sterile vortex.
Wiping the outside of all media bottles and flasks with 70% ethanol before placing them in the cabinet. (Correct answer)

Correct answer: Wiping the outside of all media bottles and flasks with 70% ethanol before placing them in the cabinet.

A fundamental principle of aseptic technique is to decontaminate the surface of all items before they enter the sterile field of the BSC. Wiping items with 70% ethanol kills microorganisms on the container surface, preventing their introduction into the cabinet and subsequent contamination of cultures.

Question 99: What is the role of antifoam agents in fermentation?

To lower the temperature inside the bioreactor
To increase the viscosity of the culture broth
To prevent excessive foam formation that can block air filters and reduce oxygen transfer (Correct answer)
To serve as a carbon source for microbial growth

Correct answer: To prevent excessive foam formation that can block air filters and reduce oxygen transfer

Antifoam agents (e.g., silicone-based compounds) reduce surface tension to collapse foam bubbles that can clog exhaust filters and reduce oxygen transfer.

Question 100: What is the purpose of a 'seed train' in biopharmaceutical manufacturing?

To generate genetically modified seed organisms
To transport cells from one facility to another
To progressively expand cell cultures from a small vial to volumes large enough to inoculate the production bioreactor (Correct answer)
To test media formulations at small scale before production

Correct answer: To progressively expand cell cultures from a small vial to volumes large enough to inoculate the production bioreactor

A seed train is a series of sequential culture steps that expand cell numbers from a frozen working cell bank vial up to production bioreactor inoculation volume.

Question 101: What does pH control in a bioreactor typically involve?

Automated addition of acid or base in response to pH probe readings to maintain the setpoint (Correct answer)
Filtering the broth to remove acidic byproducts
Manually adjusting pH once per hour
Using unbuffered media to allow natural pH equilibration

Correct answer: Automated addition of acid or base in response to pH probe readings to maintain the setpoint

Bioreactors use feedback control loops where pH probes trigger addition of acid (e.g., HCl) or base (e.g., NaOH) to maintain the optimal pH setpoint.

Question 102: What is 'out of specification' (OOS) in the context of cGMP testing?

Equipment calibration results that fall outside maintenance intervals
Any analytical test result that falls outside the acceptance criteria established in the product specification (Correct answer)
Any result obtained from an uncalibrated instrument
A result that exceeds the upper specification limit only

Correct answer: Any analytical test result that falls outside the acceptance criteria established in the product specification

An OOS result is any analytical result that falls outside established acceptance criteria — requiring investigation before product disposition decisions.

Question 103: A biotechnician has just finished running an agarose gel stained with ethidium bromide, a known mutagen. Which of the following is the proper procedure for disposing of the used gel?

Place it in a designated, sealed hazardous waste container for ethidium bromide. (Correct answer)
Discard it in the regular trash can since the concentration is low.
Autoclave it with other biological waste to neutralize the chemical.
Rinse it thoroughly with water and then dispose of it in the biohazard bag.

Correct answer: Place it in a designated, sealed hazardous waste container for ethidium bromide.

Ethidium bromide is a hazardous chemical waste due to its mutagenic properties and must be segregated for special disposal. It should not be placed in regular trash or autoclaved, as heat does not neutralize its chemical hazard. It must be collected in a clearly labeled, sealed hazardous waste container for professional disposal.

Question 104: What is the difference between 'validation' and 'qualification' in cGMP manufacturing?

Validation applies to processes; qualification applies to equipment and facilities (Correct answer)
Validation is performed before any product is made; qualification is performed after product launch
There is no distinction — the terms are interchangeable in cGMP
Validation is performed by external auditors; qualification is performed internally

Correct answer: Validation applies to processes; qualification applies to equipment and facilities

Qualification (IQ/OQ/PQ) demonstrates that equipment and facilities perform as intended; validation demonstrates that a process consistently produces product meeting predetermined specifications.

Question 105: In a bicinchoninic acid (BCA) protein assay, what reaction produces the color change used for quantification?

Protein reacts directly with BCA to form a yellow-orange product proportional to disulfide bond content
Protein reduces Cu2+ to Cu1+ in alkaline conditions; BCA chelates Cu1+ to form a purple complex measured at 562 nm (Correct answer)
Coomassie dye binds to peptide bonds shifting absorbance proportional to total amino acid content
Ninhydrin reacts with free amino groups at 100°C to form a blue product measured at 570 nm

Correct answer: Protein reduces Cu2+ to Cu1+ in alkaline conditions; BCA chelates Cu1+ to form a purple complex measured at 562 nm

The BCA assay uses two reactions: biuret reaction where protein reduces Cu2+ to Cu1+ in alkaline conditions, then BCA chelates Cu1+ ions to form an intense purple product (λmax 562 nm).

Question 106: What is the purpose of a protease inhibitor cocktail added during cell lysis for protein extraction?

To precipitate unwanted lipids and nucleic acids from the lysate
To enhance protein solubility by breaking disulfide bonds
To prevent endogenous proteases released during cell lysis from degrading the target protein (Correct answer)
To increase protein yield by improving lysis efficiency

Correct answer: To prevent endogenous proteases released during cell lysis from degrading the target protein

Cells contain proteases that are released during lysis; protease inhibitors block these enzymes, preventing degradation of the protein of interest during extraction.

Question 107: A spectrophotometer is used to measure the optical density (OD600) of a bacterial culture. What is the purpose of the 'blank' measurement?

To zero the absorbance against the growth media so only bacterial cell density is measured (Correct answer)
To measure the maximum possible absorbance the instrument can detect
To warm up the lamp before taking sample readings
To set the instrument wavelength to 600 nm

Correct answer: To zero the absorbance against the growth media so only bacterial cell density is measured

Blanking with uninoculated media subtracts the absorbance of the media itself, ensuring the measured absorbance reflects only the bacterial cells in suspension.

Question 108: Which supplement is added to basal cell culture media to provide essential growth factors, hormones, and attachment factors?

L-glutamine
Sodium bicarbonate buffer
Antibiotic-antimycotic solution (penicillin/streptomycin)
Fetal bovine serum (FBS) (Correct answer)

Correct answer: Fetal bovine serum (FBS)

Fetal bovine serum is the most common supplement providing growth factors, hormones, adhesion proteins, and transport proteins that support cell growth and attachment.

Question 109: What is 'fed-batch fermentation'?

A process where nutrients are periodically or continuously added to the bioreactor during the run without removing broth (Correct answer)
A continuous process with constant inflow and outflow of culture broth
A fermentation that uses a fixed amount of nutrients added only at the start
A process run at alternating high and low temperatures

Correct answer: A process where nutrients are periodically or continuously added to the bioreactor during the run without removing broth

Fed-batch fermentation adds nutrients incrementally during the process to prevent substrate inhibition and extend the productive growth phase.

Question 110: What is the significance of the 'dead zone' at the front edge of a biosafety cabinet work surface?

It is reserved for waste containers
UV light exposure is strongest in this zone
Air turbulence at the cabinet opening disrupts laminar flow making this area least protected (Correct answer)
It is the cleanest area farthest from the HEPA filter

Correct answer: Air turbulence at the cabinet opening disrupts laminar flow making this area least protected

The front edge of the BSC work surface is subject to air turbulence where room air meets cabinet airflow, disrupting sterile conditions — critical work should be performed further back in the cabinet.

Question 111: A biotechnician makes an error while completing a paper-based Batch Production Record (BPR). According to cGMP Good Documentation Practices, what is the correct procedure for making the correction?

Draw a single line through the incorrect entry, write the correct information, then add one's initials and the date. (Correct answer)
Request a new, clean copy of the BPR from the Quality Assurance department and discard the one with the error.
Completely obscure the incorrect entry with a black marker and write the correct data nearby.
Use correction fluid to neatly cover the error, then write the correct information on top.

Correct answer: Draw a single line through the incorrect entry, write the correct information, then add one's initials and the date.

cGMP requires that all data corrections be traceable and that the original entry remains legible. Drawing a single line through the error, adding the correction, and then initialing and dating it ensures there is a clear, attributable audit trail for the change.

Question 112: What is the purpose of the 'transfer' step in a Western blot procedure?

To transfer primary antibody from the solution onto the gel for direct detection
To electrophoretically transfer proteins from the SDS-PAGE gel onto a membrane (nitrocellulose or PVDF) for antibody-based detection (Correct answer)
To heat the gel to transfer proteins into a concentrated band before antibody incubation
To transfer the DNA sequence information of proteins from nucleus to cytoplasm for translation

Correct answer: To electrophoretically transfer proteins from the SDS-PAGE gel onto a membrane (nitrocellulose or PVDF) for antibody-based detection

Transfer moves the separated proteins from inside the polyacrylamide gel onto a membrane surface, making them accessible for antibody binding in subsequent immunodetection steps.

Question 113: What is the purpose of immersion oil used with a 100x oil-immersion objective lens?

To increase resolution by eliminating refractive index differences between the lens and slide (Correct answer)
To lubricate the objective lens
To cool the objective lens during use
To stain the specimen for better visibility

Correct answer: To increase resolution by eliminating refractive index differences between the lens and slide

Immersion oil has the same refractive index as glass, preventing light refraction at the lens-air interface and improving resolution.

Question 114: What does the term 'sterile technique' specifically mean in a laboratory context?

Cleaning benches with 70% ethanol before work
Autoclaving all solutions used in experiments
Preventing any microorganisms from entering a sterile environment or culture (Correct answer)
Wearing gloves and a lab coat

Correct answer: Preventing any microorganisms from entering a sterile environment or culture

Sterile technique refers to the set of practices used to prevent any microorganisms from contaminating sterile materials, media, cultures, or equipment.

Question 115: Under OSHA's Bloodborne Pathogen Standard (29 CFR 1910.1030), who must be offered the hepatitis B vaccine at no cost?

Only employees who have had a previous needlestick injury
All laboratory employees regardless of job function
Any employee who voluntarily requests it
Employees with occupational exposure to blood or other potentially infectious materials (OPIM) (Correct answer)

Correct answer: Employees with occupational exposure to blood or other potentially infectious materials (OPIM)

The standard requires employers to offer hepatitis B vaccination at no cost to employees with occupational exposure risk — those whose jobs involve potential contact with blood or OPIM.

Question 116: A technician needs to accurately transfer 185 µL of a buffer solution. The lab has P20, P200, and P1000 micropipettes available. Which micropipette should be used for the highest accuracy and precision?

P1000
Any of them will work equally well
P200 (Correct answer)
P20

Correct answer: P200

The P200 micropipette, with a typical range of 20-200 µL, is the most appropriate choice. Micropipettes are most accurate and precise when used in the middle to upper portion of their specified volume range. Using a P1000 for 185 µL would be at the low end of its range (100-1000 µL or 200-1000 µL), leading to greater potential inaccuracy. A P20 (2-20 µL) cannot handle this volume.

Question 117: In what phase of the cell cycle does DNA replication occur?

G1 phase
G2 phase
S phase (Correct answer)
M phase

Correct answer: S phase

The S phase, or synthesis phase, is a critical stage within interphase of the cell cycle. During this phase, the cell meticulously replicates its entire genome, ensuring that each chromosome is duplicated. This DNA replication is essential to produce two identical sister chromatids, preparing the cell for subsequent division into two daughter cells.

Question 118: What is the mobile phase in high-performance liquid chromatography (HPLC)?

The sample injection loop
The detector used to monitor separation
The column packing material
The liquid solvent pumped through the column (Correct answer)

Correct answer: The liquid solvent pumped through the column

In HPLC, the mobile phase is the liquid solvent mixture that carries the sample through the stationary phase under high pressure.

Question 119: What is cell cycle arrest and in what context is it relevant in biotechnology?

The temporary or permanent pausing of the cell cycle at specific checkpoints in response to internal or external signals (Correct answer)
The process by which cells stop dividing after reaching 100% confluency in culture
The conversion of a cell from proliferative to differentiated state
The permanent death of a cell due to DNA damage

Correct answer: The temporary or permanent pausing of the cell cycle at specific checkpoints in response to internal or external signals

Cell cycle arrest is the pausing of cell cycle progression at checkpoints in response to DNA damage, nutrient deprivation, or signaling, preventing damaged cells from dividing.

Question 120: What is the purpose of contact inhibition in normal (non-transformed) cell cultures?

To maintain sterility by inhibiting bacterial cell-to-cell contact
To prevent cells from detaching from the culture flask surface
To stop proliferation when cells make contact with neighboring cells preventing overgrowth beyond a monolayer (Correct answer)
To prevent microbial contamination when cell monolayers become dense

Correct answer: To stop proliferation when cells make contact with neighboring cells preventing overgrowth beyond a monolayer

Contact inhibition is a normal growth control mechanism where cells stop proliferating when they make contact with neighboring cells, limiting growth to a single, confluent monolayer.

Question 121: Under 21 CFR Part 211, what are the minimum data integrity requirements for original laboratory records?

Records only need to be kept for GMP-critical tests; routine measurements are exempt
Records must be made at the time of performance, be attributable (signed/initialed), legible, original, and accurate (ALCOA principles) (Correct answer)
Electronic records are not permitted — only paper records satisfy 21 CFR requirements
Records may be kept in any format as long as they are legible and available for inspection

Correct answer: Records must be made at the time of performance, be attributable (signed/initialed), legible, original, and accurate (ALCOA principles)

Data integrity under ALCOA requires that all records be Attributable, Legible, Contemporaneous, Original, and Accurate — these principles apply to both paper and electronic records.

Question 122: What equipment is required to accurately prepare a 1.00 M NaCl solution in a volume of exactly 100 mL?

A 100 mL volumetric flask, an analytical balance, and a magnetic stir plate (Correct answer)
A 250 mL Erlenmeyer flask, a digital scale, and a hot plate
A 100 mL beaker, a triple beam balance, and distilled water
A beaker, a top-loading balance, and a graduated cylinder

Correct answer: A 100 mL volumetric flask, an analytical balance, and a magnetic stir plate

A volumetric flask provides exact final volume, an analytical balance provides accurate mass measurement — both are required for a 1.00 M concentration with proper significant figures.

Question 123: In a cGMP-compliant facility, which department is primarily responsible for the hands-on testing of raw materials, in-process samples, and finished products against established specifications?

Quality Control (QC) (Correct answer)
Research and Development (R&D)
Quality Assurance (QA)
Manufacturing

Correct answer: Quality Control (QC)

Quality Control (QC) is the operational unit responsible for performing the physical and chemical tests on samples to ensure they meet predetermined specifications. Quality Assurance (QA) is responsible for the overall quality system and processes to prevent errors, but does not typically perform the routine lab testing.

Question 124: What is a chromatogram?

A diagram of the chromatography apparatus
A map of the column's pore structure
A plot of detector signal versus elution volume or time (Correct answer)
A table of fraction absorbance values

Correct answer: A plot of detector signal versus elution volume or time

A chromatogram is a graphical output showing detector signal (e.g., UV absorbance) on the Y-axis versus elution volume or time on the X-axis, with peaks representing separated components.

Question 125: Which of the following actions would most likely introduce contamination into a sterile cell culture flask?

Briefly resting the culture flask cap on a clean bench surface outside the hood (Correct answer)
Using sterile disposable pipettes
Working inside a laminar flow hood
Flaming the neck of a glass flask before pouring

Correct answer: Briefly resting the culture flask cap on a clean bench surface outside the hood

Placing a culture flask cap on an external bench surface exposes it to environmental microorganisms, which can then contaminate the culture when the cap is replaced.

Question 126: A biotechnician is preparing to cryopreserve a cell line. What is the primary role of adding dimethyl sulfoxide (DMSO) to the freezing medium?

It triggers the cells to enter a state of suspended animation.
It prevents the formation of large intracellular ice crystals that can damage cell membranes. (Correct answer)
It acts as a primary nutrient source for the cells while frozen.
It serves as a selective agent to kill any contaminating cells.

Correct answer: It prevents the formation of large intracellular ice crystals that can damage cell membranes.

DMSO is a cryoprotectant that lowers the freezing point and, most importantly, prevents the formation of large, damaging ice crystals inside the cells during the freezing process. This action is critical for preserving cell integrity and viability upon thawing.

Question 127: What does the term 'resolution' refer to in microscopy?

The brightness of the image
The minimum distance between two points that can be distinguished as separate (Correct answer)
The depth of field of the objective lens
The total magnification of the microscope

Correct answer: The minimum distance between two points that can be distinguished as separate

Resolution is the ability of a microscope to distinguish two closely spaced points as separate objects; higher resolution means finer detail is visible.

Question 128: What is the function of the Golgi apparatus in a eukaryotic cell?

To perform oxidative phosphorylation and produce ATP
To synthesize lipids and detoxify harmful compounds
To receive proteins from the ER, modify, sort, and package them for delivery to their final destinations (Correct answer)
To degrade damaged organelles and macromolecules by autophagy

Correct answer: To receive proteins from the ER, modify, sort, and package them for delivery to their final destinations

The Golgi apparatus receives proteins and lipids from the ER, performs post-translational modifications (glycosylation), and sorts and packages them for secretion or delivery to lysosomes, plasma membrane, or other destinations.

Question 129: What is epigenetics in the context of gene regulation?

Mutations in the DNA sequence of genes that are inherited by daughter cells
The process by which genes are transcribed faster in response to environmental signals
The study of genetic differences between species in their promoter sequences
Heritable changes in gene expression that do not involve changes in the DNA nucleotide sequence (e.g., methylation, histone modification) (Correct answer)

Correct answer: Heritable changes in gene expression that do not involve changes in the DNA nucleotide sequence (e.g., methylation, histone modification)

Epigenetics refers to heritable changes in gene expression or chromatin structure that do not alter the underlying DNA sequence — including DNA methylation and histone modifications.

Question 130: What is the purpose of the CO2 in a cell culture incubator?

To maintain media pH by equilibrating with bicarbonate-buffered media (Correct answer)
To prevent oxygen toxicity to cells
To provide carbon for cell metabolism
To sterilize the incubator interior

Correct answer: To maintain media pH by equilibrating with bicarbonate-buffered media

CO2 (typically 5%) dissolves in the bicarbonate-buffered media, forming carbonic acid that maintains the media pH at approximately 7.2-7.4.

Question 131: What distinguishes a 'Class 100' (ISO 5) cleanroom from a 'Class 10,000' (ISO 7) cleanroom?

Class 100 requires more employees per shift than Class 10,000
Class 100 has a maximum of approximately 3,520 particles ≥0.5 µm per m³ (very clean); Class 10,000 allows up to 352,000 particles per m³ (Correct answer)
Class 100 is for biologics only; Class 10,000 is for chemical pharmaceuticals only
Class 100 uses HEPA filtration; Class 10,000 uses standard air conditioning filters

Correct answer: Class 100 has a maximum of approximately 3,520 particles ≥0.5 µm per m³ (very clean); Class 10,000 allows up to 352,000 particles per m³

Cleanroom classifications define the maximum allowable particle counts per volume of air; ISO 5 (Class 100) is far cleaner than ISO 7 (Class 10,000) and requires more stringent controls.

Question 132: When using a vortex mixer, what is the appropriate technique for mixing a small volume (100 µL) in a microcentrifuge tube?

Press the tube bottom against the vortex pad at a slight angle at medium-low speed (Correct answer)
Set vortex to maximum speed and hold tube sideways in contact with the spinning platform
Invert the tube several times by hand instead since vortexing is not appropriate for small volumes
Place tube in a tube rack and turn the vortex to continuous mode

Correct answer: Press the tube bottom against the vortex pad at a slight angle at medium-low speed

For small volumes, pressing the tube bottom onto the vortex pad at an angle at medium speed creates a whirlpool inside the tube without risk of tube breakage or splashing.

Question 133: What is 'downstream processing' in the context of biopharmaceutical manufacturing?

The storage and distribution of raw materials
The sterilization of equipment before a production run
The series of steps used to isolate and purify the biological product from the fermentation broth (Correct answer)
The inoculation of cells into production bioreactors

Correct answer: The series of steps used to isolate and purify the biological product from the fermentation broth

Downstream processing includes all purification steps after fermentation — such as centrifugation, filtration, and chromatography — to obtain a pure final product.

Question 134: What is the primary function of the ribosome in the cell?

Producing proteins (Correct answer)
Storing lipids
Breaking down carbohydrates
Synthesizing DNA

Correct answer: Producing proteins

The ribosome is a crucial cellular organelle responsible for protein synthesis, a process also known as translation. It reads messenger RNA (mRNA) sequences and uses this genetic information to assemble amino acids into functional proteins. This function is fundamental for all cellular activities, as proteins perform a vast array of roles from structural support to enzymatic catalysis.

Question 135: What is the correct order of operations when beginning work in a biological safety cabinet?

Wipe with ethanol then turn on blower then immediately begin work
Turn on UV light then turn on blower then begin work immediately
Load materials then turn on blower then wait 5 min then begin work
Turn on blower then wait 5 min for airflow to stabilize then wipe with 70% ethanol then begin work (Correct answer)

Correct answer: Turn on blower then wait 5 min for airflow to stabilize then wipe with 70% ethanol then begin work

The BSC blower must be running and airflow must stabilize before work begins; surfaces are then decontaminated with 70% ethanol before introducing materials.

Question 136: What does 'affinity chromatography' exploit to purify a specific protein from a complex mixture?

Differences in protein surface charge at a specific pH
The specific, reversible, non-covalent interaction between the target protein and an immobilized ligand (Correct answer)
Size differences between the target protein and contaminants
Differences in protein solubility in organic solvents

Correct answer: The specific, reversible, non-covalent interaction between the target protein and an immobilized ligand

Affinity chromatography uses a column containing an immobilized ligand that specifically binds the target protein; after washing away non-binding proteins, the target is eluted by disrupting the interaction.

Question 137: How do you prepare 100 mL of a 20% (v/v) ethanol solution from pure (100%) ethanol?

Add 20 mL of 100% ethanol to a 100 mL volumetric flask and fill to the mark with water (Correct answer)
Add 20 mL of water to 80 mL of 100% ethanol in a 100 mL flask
Dilute 100 mL of ethanol with enough water to make 20 mL total volume
Add 100 mL of ethanol to 20 mL of water and mix

Correct answer: Add 20 mL of 100% ethanol to a 100 mL volumetric flask and fill to the mark with water

A 20% v/v solution requires 20 mL of ethanol per 100 mL total volume. Add 20 mL of ethanol to a 100 mL volumetric flask and fill to the 100 mL mark with water.

Question 138: While transferring a concentrated acid from a large bottle to a smaller one, a technician spills approximately 200 mL on the laboratory floor. What should be their FIRST action?

Use a spill kit to contain and absorb the acid.
Alert nearby personnel and the lab supervisor of the spill. (Correct answer)
Pour a strong base over the spill to neutralize it.
Immediately wipe up the spill with paper towels and dispose of them in the trash.

Correct answer: Alert nearby personnel and the lab supervisor of the spill.

In any significant spill, the immediate priority is human safety. Alerting others in the area and notifying a supervisor prevents accidental exposure and ensures the proper institutional emergency response is initiated. Containing and cleaning the spill is a critical subsequent step, but notification comes first.

Question 139: Which type of RNA carries the genetic code from the nucleus to the ribosome?

rRNA
mRNA (Correct answer)
tRNA
siRNA

Correct answer: mRNA

Messenger RNA (mRNA) plays a crucial role in gene expression by carrying the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm. It acts as an intermediary, translating the DNA sequence into a sequence of codons that specify the order of amino acids for protein synthesis. Without mRNA, the genetic instructions stored in DNA could not be used to build proteins.

Question 140: A biotechnician uses a spectrophotometer to measure the concentration of a purified protein by reading the absorbance at 280 nm (A280). This direct measurement method relies on the presence of which specific components within the protein?

Aromatic amino acids like tryptophan and tyrosine (Correct answer)
Peptide bonds
Proline and glycine residues
Basic amino acids like lysine and arginine

Correct answer: Aromatic amino acids like tryptophan and tyrosine

The basis for direct UV protein quantification at 280 nm is the absorbance of light by the aromatic side chains of specific amino acids, primarily tryptophan and tyrosine, and to a lesser extent, cysteine-cysteine disulfide bonds. Proteins lacking these residues cannot be quantified by this method.

Question 141: Which microscopy technique is most suitable for observing live, unstained, transparent specimens?

Bright-field microscopy
Electron microscopy
Phase-contrast microscopy (Correct answer)
Confocal microscopy

Correct answer: Phase-contrast microscopy

Phase-contrast microscopy converts differences in light phase (caused by specimen thickness/density) into visible contrast without requiring staining.

Question 142: Which of the following structures is responsible for energy production in eukaryotic cells?

Lysosome
Mitochondria (Correct answer)
Nucleus
Ribosome

Correct answer: Mitochondria

Mitochondria are often referred to as the 'powerhouses' of the cell because they are responsible for generating most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy. This vital process, known as cellular respiration, occurs within the mitochondria of eukaryotic cells. Other organelles like the nucleus, ribosome, and lysosome have different primary functions.

Question 143: What is the purpose of using a 0.22 µm membrane filter when preparing cell culture media supplements?

To remove pH indicator dyes from the supplement
To remove endotoxins from the solution
To sterilize the solution by removing bacteria and larger microorganisms (Correct answer)
To concentrate the solution by removing water

Correct answer: To sterilize the solution by removing bacteria and larger microorganisms

A 0.22 µm filter physically removes bacteria and fungi, sterilizing heat-sensitive solutions that cannot be autoclaved.

Question 144: What does 'Risk Group 2' designation mean for a biological agent under NIH/CDC guidelines?

The agent is not known to cause disease in healthy humans and poses minimal hazard
The agent causes serious or lethal disease with significant transmission risk; restricted access required
The agent poses extreme risk of life-threatening disease with no available treatment or vaccine
The agent is associated with human disease of varying severity; hazard to laboratory workers is moderate; risk to community is limited with effective prophylaxis/treatment available (Correct answer)

Correct answer: The agent is associated with human disease of varying severity; hazard to laboratory workers is moderate; risk to community is limited with effective prophylaxis/treatment available

Risk Group 2 agents cause human disease of moderate severity; they present limited risk to the community and have available treatments/prophylaxis — corresponding to BSL-2 containment.

Question 145: What is the total magnification when using a 10x eyepiece with a 40x objective lens on a compound microscope?

50x
4000x
400x (Correct answer)
4x

Correct answer: 400x

Total magnification is calculated by multiplying the eyepiece magnification (10x) by the objective lens magnification (40x), giving 400x.

Question 146: What is the Michaelis-Menten constant (Km) a measure of?

The optimal pH at which an enzyme has maximum activity
The substrate concentration at which the reaction rate is half of Vmax reflecting the affinity of the enzyme for its substrate (Correct answer)
The rate at which an enzyme-substrate complex dissociates back to free enzyme and substrate
The maximum rate of an enzyme-catalyzed reaction when substrate is saturating

Correct answer: The substrate concentration at which the reaction rate is half of Vmax reflecting the affinity of the enzyme for its substrate

Km is the substrate concentration at which reaction rate = Vmax/2. A low Km indicates high affinity (enzyme is half-saturated at low substrate concentration); a high Km indicates low affinity.

Question 147: A new bioreactor is installed in a cGMP manufacturing suite. The process of generating documented evidence that the equipment has been installed correctly and according to the manufacturer's specifications is known as:

Installation Qualification (IQ) (Correct answer)
Performance Qualification (PQ)
Operational Qualification (OQ)
Process Validation (PV)

Correct answer: Installation Qualification (IQ)

Installation Qualification (IQ) is the documented verification that equipment and its components have been properly installed and configured according to the manufacturer's specifications and design requirements. It is the first step in the equipment qualification process, followed by Operational Qualification (OQ) and Performance Qualification (PQ).

Question 148: Which of the following is NOT a physical indicator of contamination in a mammalian cell culture?

Cells growing in a monolayer as expected (Correct answer)
Visible mycelial filaments in the culture flask
Presence of floating particles or unusual debris
Color change of phenol red pH indicator in the media

Correct answer: Cells growing in a monolayer as expected

Cells growing in a normal monolayer is an expected, healthy finding — not an indicator of contamination. The other options all signal potential contamination.

Question 149: During a manufacturing run, a technician discovers that a critical buffer was prepared using an uncalibrated pH meter. This event represents a departure from the approved Standard Operating Procedure (SOP). Under cGMP, what is this event called?

An Audit Finding
A Deviation (Correct answer)
A Corrective Action
A Validation Failure

Correct answer: A Deviation

A deviation is any departure from an approved instruction, procedure, specification, or established standard. Using an uncalibrated instrument is a clear departure from the established procedure and must be documented and investigated as a deviation.

Question 150: Which piece of equipment is most accurate for measuring liquid volumes?

Erlenmeyer flask
Beaker
Graduated cylinder
Pipette (Correct answer)

Correct answer: Pipette

Pipettes are specifically designed for highly accurate and precise measurement and transfer of liquid volumes, especially small ones. Unlike beakers or graduated cylinders, which are used for approximate measurements, pipettes (such as volumetric or micropipettes) are calibrated to deliver exact volumes. This precision is critical in many laboratory procedures, including preparing reagents and performing quantitative assays.

Question 151: When performing an autoclave validation, what biological indicator organism is typically used?

Escherichia coli spores
Staphylococcus aureus vegetative cells
Geobacillus stearothermophilus spores (Correct answer)
Candida albicans spores

Correct answer: Geobacillus stearothermophilus spores

Geobacillus stearothermophilus spores are the standard biological indicator for steam autoclave validation because they are among the most heat-resistant organisms known.

Question 152: A protocol requires a 1:5 serial dilution series starting with a 1 mg/mL protein stock. What is the protein concentration of the third dilution in the series?

0.04 mg/mL
0.001 mg/mL
0.2 mg/mL
0.008 mg/mL (Correct answer)

Correct answer: 0.008 mg/mL

Each 1:5 dilution divides the concentration by 5. Starting at 1 mg/mL: 1st dilution = 0.2 mg/mL, 2nd = 0.04 mg/mL, 3rd = 0.008 mg/mL.

Question 153: What does 'in-process control' (IPC) testing mean in bioprocessing?

Testing the final product before release to confirm it meets specifications
Monitoring and testing critical parameters during manufacturing to ensure the process is performing within defined limits (Correct answer)
Calibrating instruments before starting a production run
Auditing the manufacturing facility for GMP compliance

Correct answer: Monitoring and testing critical parameters during manufacturing to ensure the process is performing within defined limits

In-process controls are measurements taken during production (e.g., cell viability, pH, osmolality, titer) to detect deviations and ensure process consistency.

BACE Biotechnician Assistant Credentialing Exam

The BACE exam credentials entry-level biotechnicians with 153 questions over 180 minutes, covering laboratory safety, biological principles, instrumentation, solution preparation, and bioprocessing.

153

Questions

180 min

Time Limit

60%

To Pass

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