BACE Biotechnician Assistant Credentialing Exam — Questions and Answers

Question 1: What is the purpose of a 'lockout/tagout' (LOTO) procedure in a laboratory setting?

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

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

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

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 3: What is the correct procedure when switching from a lower to a higher power objective lens on a microscope?

Use the coarse focus adjustment to refocus the image
Increase the light intensity before switching objectives
Rotate the nosepiece while watching from the side, then use only the fine focus adjustment (Correct answer)
Remove the slide and reposition it before switching

Correct answer: Rotate the nosepiece while watching from the side, then use only the fine focus adjustment

When switching to a higher power objective, only the fine focus is used since the microscope is parfocal and coarse adjustment could damage the lens or slide.

Question 4: A spectrophotometer is used to measure the optical density (OD600) of a bacterial culture. What is the purpose of the 'blank' measurement?

To warm up the lamp before taking sample readings
To set the instrument wavelength to 600 nm
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

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 5: The cGMP data integrity principle of 'ALCOA+' ensures that documentation is reliable. The 'C' in ALCOA+ stands for which of the following?

Contemporaneous (Correct answer)
Consistent
Controlled
Complete

Correct answer: Contemporaneous

The 'C' in the ALCOA acronym stands for Contemporaneous, which means that all activities, events, or data should be recorded at the time they are performed or observed. This practice ensures accuracy and prevents data integrity issues like backdating.

Question 6: 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.
Immediately wipe up the spill with paper towels and dispose of them in the trash.
Pour a strong base over the spill to neutralize it.
Alert nearby personnel and the lab supervisor of the spill. (Correct answer)

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 7: 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 10 mL of stock solution with 90 mL of diluent. (Correct answer)
Mix 90 mL of stock solution with 10 mL of diluent.
Mix 10 mL of stock solution with 100 mL of diluent.
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 8: What type of eye protection is required when working with potentially infectious biological materials or chemical splashes?

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

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 9: What are the monomers of proteins?

Nucleotides
Fatty acids
Amino acids (Correct answer)
Monosaccharides

Correct answer: Amino acids

Proteins are large, complex macromolecules essential for virtually every cellular process. Their fundamental building blocks, or monomers, are amino acids. These amino acids link together via peptide bonds to form long polypeptide chains, which then fold into specific three-dimensional structures to become functional proteins.

Question 10: What is the principle of size-exclusion chromatography (SEC, or gel filtration) for protein separation?

Proteins are separated by affinity for the stationary phase based on their surface hydrophobicity
Proteins with different isoelectric points are separated by a pH gradient applied across the column
Proteins are separated based on different binding affinities for immobilized antibodies on the column
Small proteins enter pores in the gel matrix and elute last; large proteins excluded from pores elute first in order of decreasing size (Correct answer)

Correct answer: Small proteins enter pores in the gel matrix and elute last; large proteins excluded from pores elute first in order of decreasing size

SEC separates proteins by size: large proteins excluded from pores elute first, while small proteins enter pores, take a longer path, and elute later.

Question 11: Which component of the cell membrane is primarily responsible for selective permeability?

Proteins
Carbohydrates
Nucleic acids
Phospholipids (Correct answer)

Correct answer: Phospholipids

Phospholipids are the primary structural components of the cell membrane, forming a bilayer. Their amphipathic nature, with hydrophilic heads and hydrophobic tails, creates a barrier that selectively regulates the passage of substances into and out of the cell. This phospholipid bilayer acts as the fundamental gatekeeper, allowing small, nonpolar molecules to pass while restricting larger or charged molecules.

Question 12: What is the correct procedure for calibrating a micropipette before use?

Rinse the tip three times with the solution before dispensing
Check that the plunger moves smoothly with no resistance
Run the pipette at full speed for 5 minutes to warm up the mechanism
Pipette a known volume of water and weigh it on an analytical balance to verify accuracy (Correct answer)

Correct answer: Pipette a known volume of water and weigh it on an analytical balance to verify accuracy

Gravimetric calibration — pipetting water and weighing it — uses the known density of water (1.0 g/mL) to verify that the delivered volume matches the set volume.

Question 13: Which piece of equipment is most accurate for measuring liquid volumes?

Pipette (Correct answer)
Graduated cylinder
Erlenmeyer flask
Beaker

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 14: Which organelle is responsible for packaging and modifying proteins for transport?

Cytoplasm
Golgi apparatus (Correct answer)
Endoplasmic reticulum
Lysosome

Correct answer: Golgi apparatus

The Golgi apparatus, also known as the Golgi complex or Golgi body, plays a central role in the endomembrane system. It receives proteins and lipids from the endoplasmic reticulum, further modifies them, sorts them, and then packages them into vesicles. These vesicles are then transported to their final destinations, either within the cell or for secretion outside the cell.

Question 15: In cGMP, what is a CAPA (Corrective and Preventive Action) system designed to accomplish?

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

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 16: Which type of pipette is most appropriate for accurately transferring exactly 15.7 mL of a solution?

A 20 mL graduated (Mohr) pipette (Correct answer)
A 25 mL volumetric pipette
A 100 µL micropipette
A 10 mL serological pipette

Correct answer: A 20 mL graduated (Mohr) pipette

A graduated (Mohr) pipette allows delivery of any volume within its range by reading the graduated scale, making 15.7 mL achievable with a 20 mL graduated pipette.

Question 17: What equipment is required to accurately prepare a 1.00 M NaCl solution in a volume of exactly 100 mL?

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

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

A molecule binds an allosteric site and changes enzyme conformation to reduce activity regardless of substrate concentration
A molecule permanently inactivates the enzyme by covalently modifying the active site
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)
A molecule binds covalently to the active site only when substrate is also bound

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

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

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 20: 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)
Operational Qualification (OQ)
Process Validation (PV)
Performance Qualification (PQ)

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 21: 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)
Autoclave it with other biological waste to neutralize the chemical.
Discard it in the regular trash can since the concentration is low.
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 22: When should you use trypan blue dye when working with cell cultures?

To stain cells for visualization under a fluorescence microscope
To assess cell viability by distinguishing live cells (exclude dye) from dead cells (take up dye) (Correct answer)
To buffer the cell suspension during centrifugation
To neutralize trypsin after cell detachment

Correct answer: To assess cell viability by distinguishing live cells (exclude dye) from dead cells (take up dye)

Trypan blue is a vital dye excluded by live cells with intact membranes; dead cells with damaged membranes take up the dye and appear blue, enabling viability counting.

Question 23: 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 sample contains high molecular weight, undigested genomic DNA. (Correct answer)
The sample contains very small DNA fragments.
The electrophoresis was run for too long.

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 24: What is the function of a DNA ladder (molecular weight marker) in gel electrophoresis?

It provides a set of DNA fragments of known sizes to estimate the size of unknown fragments (Correct answer)
It stains only linear DNA distinguishing it from circular forms
It provides fluorescent dye to visualize all DNA bands on the gel
It adjusts the electrical current to ensure consistent band migration

Correct answer: It provides a set of DNA fragments of known sizes to estimate the size of unknown fragments

A DNA ladder contains multiple DNA fragments of precisely known sizes, allowing estimation of unknown fragment sizes by comparing their migration distance to the ladder pattern.

Question 25: 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?

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

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

Because temperature affects enzyme activity, cell growth rate, product formation, and product quality (Correct answer)
Because temperature controls the pH of the culture broth
Because low temperatures increase the dissolved oxygen level in the media
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 27: 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 28: What is a bioreactor primarily used for in biotechnology?

To separate proteins by molecular weight
To store biological samples at low temperatures
To provide a controlled environment for growing microorganisms or cells to produce biological products (Correct answer)
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 29: A technician is passaging an adherent mammalian cell line. Which of the following reagents is commonly used to enzymatically detach the cells from the surface of the culture flask?

Trypsin-EDTA (Correct answer)
Fetal Bovine Serum (FBS)
Phosphate-Buffered Saline (PBS)
Dimethyl sulfoxide (DMSO)

Correct answer: Trypsin-EDTA

Trypsin is a proteolytic enzyme that cleaves the proteins cells use to attach to the flask surface. EDTA is a chelating agent that binds calcium and magnesium ions, which further disrupts cell adhesion.

Question 30: What is the proper first response action when a researcher spills a small volume of a mildly corrosive acid (dilute HCl) on their bare forearm?

Apply an acid burn ointment from the first aid kit and cover with a bandage
Apply sodium bicarbonate paste immediately to neutralize the acid
Remove clothing and report to a supervisor before rinsing
Immediately flush the affected area with large amounts of water for at least 15-20 minutes (Correct answer)

Correct answer: Immediately flush the affected area with large amounts of water for at least 15-20 minutes

Immediate and copious water flushing for 15-20 minutes dilutes and removes the acid, minimizing tissue damage — neutralization pastes can cause exothermic reactions and should not be applied first.

Question 31: 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 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.
The rate of reduction of copper ions by the protein.

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 32: What is restriction fragment length polymorphism (RFLP) analysis used for?

Measuring the concentration of DNA in a solution
Identifying DNA sequence differences between individuals by digesting DNA with restriction enzymes and comparing fragment sizes (Correct answer)
Sequencing the complete genome of an organism
Amplifying specific DNA sequences using thermal cycling

Correct answer: Identifying DNA sequence differences between individuals by digesting DNA with restriction enzymes and comparing fragment sizes

RFLP analysis detects DNA sequence variations by using restriction enzymes to cut DNA at specific recognition sites; sequence differences create different fragment size patterns on gels.

Question 33: What is 'downstream processing' in the context of biopharmaceutical manufacturing?

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
The storage and distribution of raw materials

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 34: A researcher is working with human-derived cell lines, which are considered potentially infectious materials under most circumstances. According to OSHA's Bloodborne Pathogens Standard, which of the following is the MOST appropriate combination of engineering controls and personal protective equipment (PPE)?

A Class II Biosafety Cabinet, lab coat, and gloves. (Correct answer)
A respirator and chemical splash goggles.
A standard lab coat and safety glasses.
A chemical fume hood and nitrile gloves.

Correct answer: A Class II Biosafety Cabinet, lab coat, and gloves.

OSHA considers human cell lines to be potentially infectious materials. A Class II Biosafety Cabinet is an engineering control that protects the user from bioaerosols, the environment, and the sample from contamination. A lab coat and gloves are the minimum required PPE for handling such materials at Biosafety Level 2.

Question 35: Which of the following is considered a source of chemical contamination in a cell culture, rather than biological contamination?

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

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 36: 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 centrifuge large volumes of culture broth
To filter sterile air into the bioreactor

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 37: What is 'scale-up' in bioprocessing?

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

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

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

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 39: Which element is the backbone of organic molecules?

Nitrogen
Carbon (Correct answer)
Phosphorus
Oxygen

Correct answer: Carbon

Carbon is the backbone of all organic molecules due to its unique ability to form four stable covalent bonds with other atoms, including other carbon atoms. This tetravalency allows carbon to create diverse and complex molecular structures, such as long chains, branched structures, and rings. These intricate carbon frameworks are essential for the vast array of biological molecules that make up living organisms.

Question 40: In batch fermentation, when does the 'stationary phase' occur?

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

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

Mitochondria (Correct answer)
Ribosome
Nucleus
Endoplasmic reticulum

Correct answer: Mitochondria

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

Question 42: 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?

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

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

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

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 44: 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?

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

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

Confocal microscopy
Phase-contrast microscopy (Correct answer)
Electron microscopy
Bright-field 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 46: What is 'upstream processing' in bioprocessing?

All steps involved in growing and harvesting cells or microorganisms, including media preparation and fermentation (Correct answer)
Formulation and packaging of the product
The purification of the final biological product
Quality control testing of the finished 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 47: What is the basic unit of heredity?

Protein
Chromosome
DNA
Gene (Correct answer)

Correct answer: Gene

A gene is the basic unit of heredity, consisting of a specific sequence of DNA (or RNA in some viruses). Each gene carries the instructions for making a specific protein or functional RNA molecule, which in turn determines a particular trait or characteristic. Genes are passed from parents to offspring, transmitting genetic information across generations.

Question 48: Which type of chromatography separates proteins based on their affinity for a specific ligand?

Affinity chromatography (Correct answer)
Hydrophobic interaction chromatography
Gel filtration chromatography
Ion exchange chromatography

Correct answer: Affinity chromatography

Affinity chromatography uses a ligand bound to the stationary phase that specifically binds the target molecule, allowing highly selective purification.

Question 49: What is the purpose of using a 0.22 µm membrane filter when preparing cell culture media supplements?

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

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

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

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

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: What is the difference between a gene and an allele?

A gene is found in somatic cells; an allele is found only in germ cells
A gene is a hereditary unit encoding a trait; an allele is one of the alternative forms of that gene at a specific chromosomal locus (Correct answer)
A gene is a segment of DNA; an allele is a segment of RNA
A gene exists only in diploid organisms; an allele exists in haploid organisms

Correct answer: A gene is a hereditary unit encoding a trait; an allele is one of the alternative forms of that gene at a specific chromosomal locus

A gene is a specific DNA sequence that encodes a functional product; alleles are the different sequence variants of that gene that can exist at the same chromosomal locus.

Question 53: Which objective lens would provide the greatest working distance from the lens to the specimen?

100x (oil immersion)
4x (scanning objective) (Correct answer)
40x (high dry)
10x (low power)

Correct answer: 4x (scanning objective)

Lower magnification objectives like the 4x scanning objective have the greatest working distance, while higher magnification objectives are much closer to the specimen.

Question 54: After an affinity chromatography purification step, the column is often regenerated by:

Flushing with a regeneration solution to remove residual bound material, then re-equilibrating (Correct answer)
Autoclaving the column at 121°C
Storing it dry at room temperature
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 55: What is the purpose of contact inhibition in normal (non-transformed) cell cultures?

To prevent microbial contamination when cell monolayers become dense
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)

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 56: 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 complete inventory of all chemical quantities submitted to the EPA
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

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 57: A lab protocol requires the preparation of a 2% (w/v) agarose gel solution in a total volume of 150 mL. How much agarose powder is needed?

30.0 g
0.3 g
2.0 g
3.0 g (Correct answer)

Correct answer: 3.0 g

A weight/volume (w/v) percentage solution is defined as grams of solute per 100 mL of solution. A 2% (w/v) solution means 2 g of solute in 100 mL of solvent. To find the amount needed for 150 mL, you can set up a proportion: (2 g / 100 mL) = (x g / 150 mL). Solving for x gives: x = (2 g * 150 mL) / 100 mL = 3.0 g.

Question 58: 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 phosphate backbone of DNA carries a strong negative charge. (Correct answer)
The agarose gel matrix is positively charged.
The buffer system creates a pH gradient that attracts the DNA.

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

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

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 60: 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)
Using unbuffered media to allow natural pH equilibration
Filtering the broth to remove acidic byproducts
Manually adjusting pH once per hour

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 61: 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
Coomassie dye binds to peptide bonds shifting absorbance proportional to total amino acid content
Protein reduces Cu2+ to Cu1+ in alkaline conditions; BCA chelates Cu1+ to form a purple complex measured at 562 nm (Correct answer)
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 62: Which parameter is most critical to monitor during aerobic fermentation in a bioreactor?

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

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

To transfer the DNA sequence information of proteins from nucleus to cytoplasm for translation
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

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 64: What does 'GDP' (Good Documentation Practices) require when correcting an error in a paper record?

Draw a single line through the error, write the correction alongside, add initials, date, and reason for correction (Correct answer)
Circle the error and write the correction on a separate sticky note attached to the record
Erase or use correction fluid to remove the error before writing the correct value
Discard the page and start fresh on a new sheet

Correct answer: Draw a single line through the error, write the correction alongside, add initials, date, and reason for correction

GDP requires a single strikethrough that keeps the original entry readable, with the correction, signature/initials, date, and reason noted — never erasing or obscuring original entries.

Question 65: A laboratory stock solution of HCl is labeled '12 M'. How much stock is needed to make 100 mL of 1 M HCl?

8.33 mL (Correct answer)
120 mL
1.2 mL
12 mL

Correct answer: 8.33 mL

Using C1V1 = C2V2: (12 M)(V1) = (1 M)(100 mL), so V1 = 100/12 = 8.33 mL of stock.

Question 66: When dissolving a solute in water, what step should be done first?

Add water to the final volume
Heat the solution
Stir 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 67: 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)

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

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

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

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 69: What does SEM (Scanning Electron Microscopy) primarily image?

The surface topography of specimens (Correct answer)
Fluorescently labeled proteins
DNA and RNA molecules directly
The internal structure of cells

Correct answer: The surface topography of specimens

SEM scans a focused electron beam over the specimen surface, detecting secondary electrons to create three-dimensional surface images.

Question 70: 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)
Basic amino acids like lysine and arginine
Proline and glycine residues
Peptide bonds

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

mRNA (Correct answer)
rRNA
siRNA
tRNA

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

To generate genetically modified seed organisms
To test media formulations at small scale before production
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)

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 73: A biotechnician is performing a plasmid DNA extraction from E. coli using a spin-column based kit. The final step involves adding an elution buffer to the silica membrane. What is the primary purpose of this step?

To precipitate the plasmid DNA out of the solution.
To digest any remaining RNA in the sample.
To wash away any remaining proteins and salts.
To release the bound plasmid DNA from the silica membrane. (Correct answer)

Correct answer: To release the bound plasmid DNA from the silica membrane.

In spin-column based DNA extraction, DNA binds to the silica membrane under high-salt conditions. The final step uses a low-salt elution buffer to decrease the affinity of the DNA for the silica, allowing the purified DNA to be released from the column and collected.

Question 74: What does the term 'passage number' refer to in cell culture?

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

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

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)
The media pH has shifted due to CO2 levels

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

Tris was purchased as the pre-made HCl salt and dissolved to pH 8.0 without adjustment
Only Tris base was used and the final pH happened to be 8.0
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)
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 77: What is the total magnification when using a 10x eyepiece with a 40x objective lens on a compound microscope?

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

Correct answer: 400x

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

Question 78: What is a 'wet mount' preparation in light microscopy?

A specimen suspended in a drop of liquid between a slide and coverslip (Correct answer)
A slide that has been washed with water before use
A slide stored in humid conditions
A preparation using water-soluble stains

Correct answer: A specimen suspended in a drop of liquid between a slide and coverslip

A wet mount places a specimen in a drop of water or buffer covered by a coverslip, allowing observation of live or unstained specimens.

Question 79: What type of electron microscopy is used to examine the internal ultrastructure of thin-sectioned specimens?

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

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

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

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 81: What is the difference between hydrophilic and hydrophobic amino acid residues in a protein and how does this affect protein folding?

Hydrophilic residues form disulfide bonds; hydrophobic residues form hydrogen bonds in the protein interior
Hydrophilic residues carry a positive charge; hydrophobic residues carry a negative charge
Hydrophilic residues are found in alpha helices; hydrophobic residues are found in beta sheets
Hydrophilic residues interact favorably with water and are found on the protein surface; hydrophobic residues avoid water and pack into the protein interior during folding (Correct answer)

Correct answer: Hydrophilic residues interact favorably with water and are found on the protein surface; hydrophobic residues avoid water and pack into the protein interior during folding

Hydrophobic residues with nonpolar side chains minimize contact with water by packing into the protein core; hydrophilic residues with polar or charged side chains interact favorably with water and face the exterior.

Question 82: What does BSL-2 (Biosafety Level 2) designation mean for a laboratory agent?

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

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 83: 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 dilute the enzyme to below the concentration that causes autocatalytic degradation
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)

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

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

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 85: What is the pH of a neutral solution?

14
0
-7
7 (Correct answer)

Correct answer: 7

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 to 14. A pH of 7 indicates a neutral solution, meaning it has an equal concentration of hydrogen ions (H+) and hydroxide ions (OH-). Pure water at 25°C is a classic example of a neutral solution with a pH of 7.

Question 86: 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?

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

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 87: 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
60.57 g
121.14 g
30.29 g (Correct answer)

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 88: 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
100 U
10,000 U (Correct answer)
1,000 U

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 89: What is the significance of a cell culture 'split ratio' of 1:3?

One mL of cells is added to three mL of fresh media in the same flask
Cells from one flask are divided into three new flasks diluting density by one-third (Correct answer)
One part cells are mixed with three parts trypsin for detachment
Three flasks of cells are combined into one flask to increase density

Correct answer: Cells from one flask are divided into three new flasks diluting density by one-third

A 1:3 split ratio means cells harvested from one flask are divided equally into three new flasks, reducing the cell density to one-third and allowing room for cells to grow until the next passage.

Question 90: What is the function of NADH and FADH2 in cellular respiration?

They transport carbon dioxide from cells to the lungs for exhalation
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 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 91: 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 is a deprecated term not used in modern laboratory practice; always convert to molarity
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)

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 92: A biotechnician needs to find information on the appropriate first-aid measures to take after accidental skin contact with a chemical. Which section of the Safety Data Sheet (SDS) should they consult?

Section 2: Hazard(s) Identification
Section 8: Exposure Controls/Personal Protection
Section 4: First-Aid Measures (Correct answer)
Section 7: Handling and Storage

Correct answer: Section 4: First-Aid Measures

Section 4 of an SDS specifically details the initial care that should be given by untrained responders following exposure to the chemical, covering routes like skin/eye contact, inhalation, and ingestion.

Question 93: What is the primary function of providing a 5% CO2 atmosphere in a standard mammalian cell culture incubator?

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

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 94: A technician must transfer a sterile solution from a large bottle to a smaller container. What is the best aseptic practice?

Pour directly while holding both containers over the bench
Work inside the BSC, flame bottle neck if glass, pour without touching inside surfaces, recap immediately (Correct answer)
Transfer on the open bench after wiping with 70% ethanol
Use a syringe to withdraw through the bottle cap without opening

Correct answer: Work inside the BSC, flame bottle neck if glass, pour without touching inside surfaces, recap immediately

Inside the BSC, careful handling prevents contamination; avoiding contact with internal surfaces and recapping immediately preserves sterility.

Question 95: What is the difference between prokaryotic and eukaryotic cells?

Eukaryotes have a membrane-bound nucleus and organelles; prokaryotes lack these structures (Correct answer)
Prokaryotes have a nucleus; eukaryotes do not
Prokaryotes are larger and more complex than eukaryotes
Eukaryotes lack cell walls while prokaryotes always have them

Correct answer: Eukaryotes have a membrane-bound nucleus and organelles; prokaryotes lack these structures

Eukaryotic cells have a true membrane-bound nucleus and specialized organelles; prokaryotic cells (bacteria and archaea) lack a membrane-bound nucleus and membrane-bound organelles.

Question 96: How much NaCl (MW = 58.44 g/mol) is needed to prepare 500 mL of a 0.9% (w/v) saline solution?

0.45 g
0.9 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 97: What problem arises when PCR primers have a high degree of self-complementarity?

Primers can fold back on themselves forming hairpin structures or anneal to each other forming primer dimers reducing PCR efficiency (Correct answer)
The primers become too long and cannot bind efficiently to the template
Self-complementary primers amplify only GC-rich regions of the template
The denaturation temperature must be lowered significantly to prevent primer damage

Correct answer: Primers can fold back on themselves forming hairpin structures or anneal to each other forming primer dimers reducing PCR efficiency

Self-complementary primer sequences form intramolecular hairpins or intermolecular primer dimers that reduce the concentration of free primers available to bind the template.

Question 98: Which classification of biosafety cabinet is appropriate for working with BSL-3 pathogens?

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

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

Add sufficient quantity of solvent (Correct answer)
Add more solute
Heat to dissolve
Quantify the 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 100: What is the primary purpose of a biosafety cabinet (BSC) in a biotechnology laboratory?

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)
To centrifuge biological samples at high speed

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 101: Which of the following best describes the purpose of a 'batch record' in cGMP manufacturing?

A summary of QC test results for a batch submitted to the FDA
A financial record tracking the cost of materials used in a manufacturing batch
A record of employee training for the production team assigned to a batch
A complete chronological documentation of all steps, materials, equipment, and measurements for a specific production lot (Correct answer)

Correct answer: A complete chronological documentation of all steps, materials, equipment, and measurements for a specific production lot

A batch record (or lot record) documents every step of manufacturing for a specific lot, including materials used (lot numbers, weights), equipment, process parameters, in-process checks, and operator signatures.

Question 102: 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 quantifies the rate of oxygen consumption by the culture
It indicates the rate of pH change in the bioreactor
It measures the rate of product formation per unit time

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 103: 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?

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

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 104: 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?

A Deviation (Correct answer)
An Audit Finding
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 105: Which of the following best describes 'gradient elution' in ion exchange chromatography?

Collecting fractions at fixed time intervals
Loading the sample at increasing flow rates
Progressively increasing salt concentration in the elution buffer (Correct answer)
Decreasing column temperature during the run

Correct answer: Progressively increasing salt concentration in the elution buffer

Gradient elution involves gradually increasing the salt concentration (or changing pH) to sequentially release proteins with different affinities for the resin.

Question 106: Why must you never use a mercury thermometer in a laboratory incubator or water bath?

Mercury thermometers cannot measure temperatures above 37°C
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 expands too quickly causing inaccurate readings at higher temperatures

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 107: What is the result of a frameshift mutation in a protein-coding gene?

A shift in the reading frame that alters all downstream codons usually producing a truncated or non-functional protein (Correct answer)
Increased protein production due to creation of an alternative start codon
A single amino acid change in the resulting protein at the site of the mutation
Complete loss of gene function due to failure to transcribe the mutated DNA

Correct answer: A shift in the reading frame that alters all downstream codons usually producing a truncated or non-functional protein

A frameshift mutation (insertion or deletion of non-multiple-of-3 nucleotides) shifts the triplet codon reading frame, causing all downstream amino acids to change and often introducing premature stop codons.

Question 108: What is the role of antifoam agents in fermentation?

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

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 109: 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?

1.0 M (Correct answer)
0.1 M
2.0 M
0.5 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 110: 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)
Flaming the neck of a glass flask before pouring
Working inside a laminar flow hood
Using sterile disposable pipettes

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 111: 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)
137 mM (same as working — stocks are not more concentrated)
13.7 mM (one-tenth the working concentration)
274 mM (2x 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 112: What is the purpose of a 'Threshold Limit Value — Short Term Exposure Limit' (TLV-STEL) for a chemical?

It represents the minimum concentration detectable by human smell
It defines the maximum lifetime total dose of a chemical a worker can receive
It defines the maximum airborne concentration a worker can be exposed to for a 15-minute period without adverse effects (Correct answer)
It specifies the concentration at which a chemical becomes immediately dangerous to life or health (IDLH)

Correct answer: It defines the maximum airborne concentration a worker can be exposed to for a 15-minute period without adverse effects

TLV-STEL is the ACGIH exposure limit for short-duration (15-min) peak exposures that should not be exceeded.

Question 113: 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?

Protein C, then B, then A
Protein A, then B, then C (Correct answer)
The order depends on the charge of the proteins
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 114: What is the primary purpose of a 'Site Master File' (SMF) in pharmaceutical cGMP?

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
It provides financial accountability for all manufacturing costs
It is the internal quality manual used for employee training

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

To adjust the magnification of the eyepiece
To magnify the final image seen by the observer
To focus light onto the specimen to maximize illumination and resolution (Correct answer)
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 116: What does the term 'sterile technique' specifically mean in a laboratory context?

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

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 117: 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 stain the specimen for better visibility
To cool the objective lens during use
To lubricate the objective lens

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 118: In a Western blot procedure, what is the function of the blocking step (e.g., 5% milk or BSA)?

To transfer blocking agent onto the gel before membrane transfer to improve protein retention
To saturate non-specific protein-binding sites on the membrane preventing antibody from binding non-specifically to the membrane background (Correct answer)
To enhance antibody binding to the target protein on the membrane
To denature the primary antibody so it only detects denatured proteins on the blot

Correct answer: To saturate non-specific protein-binding sites on the membrane preventing antibody from binding non-specifically to the membrane background

Blocking covers non-specific protein-binding sites on the membrane with irrelevant proteins (milk casein, BSA), preventing primary antibody from sticking non-specifically to the membrane background.

Question 119: Which of the following activities is a core responsibility of the Quality Assurance (QA) department in a biotechnology company?

Executing the steps of a manufacturing process.
Calibrating laboratory analytical balances.
Performing identity testing on incoming raw materials.
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 120: What does 'in-process control' (IPC) testing mean in bioprocessing?

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
Testing the final product before release to confirm it meets specifications
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.

Question 121: What is the purpose of the 'stacking gel' in a discontinuous SDS-PAGE system (Laemmli system)?

The stacking gel (low % acrylamide, low pH) concentrates all proteins into a thin band before they enter the resolving gel (Correct answer)
The stacking gel resolves small proteins that the resolving gel cannot separate
The stacking gel contains the molecular weight standards for protein size estimation
The stacking gel prevents proteins from migrating until the voltage is applied

Correct answer: The stacking gel (low % acrylamide, low pH) concentrates all proteins into a thin band before they enter the resolving gel

The stacking gel (3-5% acrylamide, pH 6.8) uses the Laemmli discontinuous buffer system to concentrate proteins into a sharp band at the gel interface before they enter the resolving gel, improving band sharpness.

Question 122: What technique separates proteins based on their isoelectric point (pI)?

Gel filtration chromatography
Hydrophobic interaction chromatography
Ion exchange 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 123: What is the correct order of operations when beginning work in a biological safety cabinet?

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

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 124: What is the difference between genotype and phenotype?

Genotype is the genetic makeup (alleles) of an organism; phenotype is the observable physical or biochemical characteristics resulting from genotype and environment (Correct answer)
Genotype refers to somatic cell genetics; phenotype refers to germ cell genetics
Genotype and phenotype are synonymous terms for an organism's inherited traits
Genotype is the visible physical characteristics; phenotype is the underlying genetic makeup

Correct answer: Genotype is the genetic makeup (alleles) of an organism; phenotype is the observable physical or biochemical characteristics resulting from genotype and environment

Genotype is the specific alleles an organism carries; phenotype is the observable result of those alleles expressed in a particular environment.

Question 125: What does 'pH 7.4 with NaOH' typically mean when listed in a buffer preparation protocol?

After dissolving all buffer components, measure pH and adjust to 7.4 by adding NaOH (to raise pH) or HCl (to lower pH) dropwise (Correct answer)
Add a fixed amount of 7.4 mL of NaOH to the solution
Prepare the buffer using NaOH as the sole pH-determining component
Add NaOH until the solution becomes colorless

Correct answer: After dissolving all buffer components, measure pH and adjust to 7.4 by adding NaOH (to raise pH) or HCl (to lower pH) dropwise

Buffer protocols require pH adjustment after dissolving all components, adding NaOH to raise pH to the target value, with HCl available to correct any overshoot below target.

Question 126: Which of the following is the most critical final step before finalizing the volume of a buffer solution prepared from solid components?

Heating the solution to ensure all solutes are dissolved.
Allowing the solution to sit for at least one hour.
Vortexing the solution vigorously for five minutes.
Adjusting the pH to the desired value. (Correct answer)

Correct answer: Adjusting the pH to the desired value.

When preparing a buffer, after dissolving the solid components in a volume of solvent less than the final desired volume, the pH must be checked and adjusted. The pH can change as components dissolve. The final volume is brought up to the mark only after the pH has been correctly set.

Question 127: Which method is commonly used to separate cells from fermentation broth during harvest?

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

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

Differences in protein solubility in organic solvents
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

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 129: 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?

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

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 130: 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)
Presence of floating particles or unusual debris
Color change of phenol red pH indicator in the media
Visible mycelial filaments in the culture flask

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 131: What is 'fed-batch fermentation'?

A continuous process with constant inflow and outflow of culture broth
A process where nutrients are periodically or continuously added to the bioreactor during the run without removing broth (Correct answer)
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 132: What is the correct order of steps when beginning microscopy observation of a new slide?

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

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 133: In size exclusion chromatography (SEC), which molecules elute first?

Small molecules that enter the pores
Large molecules that are excluded from the pores (Correct answer)
Molecules of intermediate size
Charged molecules regardless of size

Correct answer: Large molecules that are excluded from the pores

Large molecules are excluded from the pores of the resin and travel around them, eluting first with the void volume.

Question 134: How often should the interior surfaces of a biological safety cabinet be decontaminated with 70% ethanol?

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

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

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

Correct answer: Gram staining

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

Question 136: When disposing of chemical waste from a laboratory, what must be present on every chemical waste container?

The date the container was filled and the name of the person who filled it
Only the hazard class symbol from the GHS system
A proper chemical waste label showing all chemical contents, associated hazards, and the generating laboratory location (Correct answer)
A manifest number assigned by the waste disposal company

Correct answer: A proper chemical waste label showing all chemical contents, associated hazards, and the generating laboratory location

EPA and RCRA regulations require chemical waste containers to be clearly labeled with all contents, their hazard characteristics, and the generating location.

Question 137: Which characteristic distinguishes a 'transformed' cell line from a 'primary' cell line?

Transformed cell lines require higher serum concentrations to maintain growth
Transformed cell lines can only be grown in suspension not adherently
Transformed cell lines have acquired the ability to grow indefinitely (immortality) due to genetic alteration (Correct answer)
Primary cell lines always grow faster than transformed lines

Correct answer: Transformed cell lines have acquired the ability to grow indefinitely (immortality) due to genetic alteration

Cell transformation confers immortality — indefinite proliferative capacity — unlike primary cells that senesce after finite passages.

Question 138: What are endotoxins and why do solution preparations for mammalian cell culture require specific testing for them?

Endotoxins are chemical preservatives added to commercial reagents that must be removed for cell culture use
Endotoxins are lipopolysaccharide (LPS) components of gram-negative bacterial cell walls that contaminate solutions and cause severe inflammatory responses in mammalian cells and animal models (Correct answer)
Endotoxins are toxic compounds that leach from plastic laboratory equipment into solutions
Endotoxins are protein aggregates that form during solution preparation and cause cell culture pH shifts

Correct answer: Endotoxins are lipopolysaccharide (LPS) components of gram-negative bacterial cell walls that contaminate solutions and cause severe inflammatory responses in mammalian cells and animal models

Endotoxins (LPS from gram-negative bacteria) are heat-stable, 0.22 µm-filter-resistant contaminants that cause TLR4-mediated inflammatory signaling in mammalian cells, affecting cell behavior and experimental results.

Question 139: Which culture mode continuously adds fresh nutrients while removing spent media at the same rate to maintain a constant volume?

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

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

SDS gives each protein a unique net charge proportional to its amino acid composition
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)
Reducing agents in the sample buffer separate proteins by charge while SDS separates by size
The polyacrylamide gel selectively binds large proteins retarding their migration based on charge density

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

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

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 142: A centrifuge rotor becomes unbalanced during a spin. What is the most immediate risk?

Overheating of the centrifuge motor
Loss of temperature control in the samples
Sample contamination from aerosols
Mechanical failure, rotor damage, or injury from rotor failure (Correct answer)

Correct answer: Mechanical failure, rotor damage, or injury from rotor failure

An unbalanced rotor generates enormous centrifugal forces that can cause catastrophic rotor failure, potentially destroying the centrifuge and injuring nearby personnel.

Question 143: What are the three critical parameters that an autoclave utilizes to achieve sterilization of laboratory equipment and media?

UV radiation, high pressure, and filtration.
Dry heat, long duration, and vacuum.
High temperature, high pressure, and steam. (Correct answer)
High pressure, low temperature, and chemical disinfectants.

Correct answer: High temperature, high pressure, and steam.

An autoclave, or steam sterilizer, sterilizes items by subjecting them to high-pressure saturated steam at a high temperature (typically 121°C or higher) for a specific amount of time. The combination of steam, pressure, and heat effectively kills all microorganisms, including resilient bacterial spores.

Question 144: What is the process by which DNA is copied into RNA?

Replication
Mutation
Translation
Transcription (Correct answer)

Correct answer: Transcription

Transcription is the process by which genetic information encoded in DNA is copied into a molecule of messenger RNA (mRNA). During transcription, an enzyme called RNA polymerase synthesizes an RNA strand that is complementary to a segment of the DNA template. This mRNA molecule then carries the genetic instructions out of the nucleus to the ribosomes for protein synthesis.

Question 145: What does a Bradford assay (Coomassie Blue dye binding) measure, and what is its color shift?

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
Lipid concentration; the dye shifts from blue to yellow in the presence of membrane lipids
Total protein concentration; Coomassie Blue shifts from reddish-brown to blue when it binds proteins under acidic conditions (Correct answer)

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

The agent causes serious or lethal disease with significant transmission risk; restricted access required
The agent is not known to cause disease in healthy humans and poses minimal hazard
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 147: 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 148: What is the Henderson-Hasselbalch equation used for in laboratory buffer preparation?

Calculating the molarity of a buffer from its weight/volume percentage
Determining the rate of enzyme-catalyzed reactions in buffered solutions
Calculating the osmolarity of a buffer solution based on its ionic composition
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)

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 149: 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?

Use correction fluid to neatly cover the error, then write the correct information on top.
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.

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

To lower media pH to enhance trypsin efficiency
To remove serum proteins that would inhibit trypsin activity (Correct answer)
To activate the trypsin enzyme before it contacts cells
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 151: In fluorescence microscopy, what does a fluorophore do when excited by light of the correct wavelength?

It absorbs all wavelengths of light equally
It generates heat to warm the specimen
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 152: What is a chromatogram?

A table of fraction absorbance values
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)

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 153: What is the molar concentration of a glucose solution prepared by dissolving 18.02 g of glucose (MW = 180.2 g/mol) in water to a final volume of 1 liter?

0.1 M (Correct answer)
0.01 M
10 M
1.0 M

Correct answer: 0.1 M

Moles of glucose = 18.02 g divided by 180.2 g/mol = 0.1 mol. Concentration = 0.1 mol / 1.0 L = 0.1 M.

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%

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