Q50. Which intestinal cestode infection is contracted by consuming undercooked beef containing infectious cysticerci larval stages? A) Taenia solium B) Taenia saginata C) Diphyllobothrium latum D) Echinococcus granulosus
Thank you for reading this post, don't forget to subscribe!Thank you for reading this post, don't forget to subscribe!- Correct Answer: B
- Rationale: Taenia saginata is known as the beef tapeworm; its larval stage (Cysticercus bovis) develops in cattle tissues, and humans contract the intestinal tapeworm by eating undercooked, contaminated beef.
Part 6: Urinalysis and Body Fluids
Q51. A urine specimen is delivered to the laboratory and left on the benchtop without preservative for 4 hours. Which of the following changes is expected due to bacterial proliferation and chemical decomposition? A) Glucose levels increase B) pH shifts from acidic to alkaline due to urea breakdown into ammonia C) Ketone body concentrations rise D) Bilirubin levels become stable
- Correct Answer: B
- Rationale: Unpreserved urine left at room temperature allows bacteria to multiply. If these bacteria produce urease, they split urea into ammonia, increasing the sample pH and making it more alkaline.
Q52. During chemical analysis of a urine sample using a commercial reagent strip, a strong positive reaction for protein is detected. This reagent strip color change relies on which chemical principle? A) The protein error of indicators B) Copper reduction reaction C) Diazotization coupling principle D) Ehrlich’s aldehyde reaction
- Correct Answer: A
- Rationale: Urinary reagent strips test for protein using the “protein error of indicators” principle, where a pH indicator dye releases hydrogen ions and shifts color in the presence of protein even while pH remains constant.
Q53. Microscopic examination of a fresh urine sediment reveals distinct colorless, clear crystals shaped like rectangular prisms or “coffin lids”. What type of crystal is this? A) Calcium oxalate crystal B) Triple phosphate crystal (Ammonium magnesium phosphate) C) Uric acid crystal D) Cystine crystal
- Correct Answer: B
- Rationale: Triple phosphate crystals form in alkaline urine and have a characteristic multi-faceted prism appearance often described as a “coffin lid.”
Q54. A patient presenting with acute glomerulonephritis undergoes urinalysis. Which microscopic element found in urine sediment provides definitive evidence of renal glomerular bleeding? A) Hyaline casts B) Red Blood Cell (RBC) casts C) Squamous epithelial cells D) Triple phosphate crystals
- Correct Answer: B
- Rationale: RBC casts form within the renal distal tubules and collecting ducts when red cells enter the nephron via a damaged glomerulus, providing definitive evidence of renal parenchymal bleeding.
Q55. A cerebrospinal fluid (CSF) sample is collected via lumbar puncture and distributed into three sequentially numbered tubes. Tubes 1, 2, and 3 all show a uniform, equal distribution of blood and do not form clots upon standing. This pattern indicates: A) A traumatic lumbar puncture puncture injury B) A true subarachnoid hemorrhage C) Normal physiological variation D) Contamination with skin bacteria
- Correct Answer: B
- Rationale: In a subarachnoid hemorrhage, blood is distributed evenly throughout the CSF space, so sequentially collected tubes show a uniform red color. A traumatic puncture typically shows decreasing blood discoloration from Tube 1 to Tube 3.
Q56. A pleural fluid sample is analyzed in a laboratory. The fluid has a total protein ratio of 0.65 compared to serum, an LDH ratio of 0.80, and appears turbid. How should this serous fluid be classified? A) Transudate B) Exudate C) Normal mucus secretion D) Synovial ultrafiltrate
- Correct Answer: B
- Rationale: According to Light’s criteria, a pleural fluid to serum total protein ratio >0.5 and an LDH ratio >0.6 classifies the fluid as an exudate, which points to an inflammatory or infectious process affecting the serous membranes.
Q57. Which chemical test can be used as a confirmatory method to detect urinary bilirubin if a reagent strip gives a questionable or trace positive result? A) Clinitest tablet method B) Ictotest tablet method C) Sulfosalicylic Acid (SSA) precipitation test D) Acetest method
- Correct Answer: B
- Rationale: The Ictotest is a specific, sensitive diazotization tablet test used to confirm the presence of bilirubin in urine at lower detection thresholds than standard dipsticks.
Q58. While looking at an acidic urine sediment sample, the technician notices unique hexagonal, colorless plates that resemble stop signs. This finding is linked to an inherited metabolic disorder involving which amino acid? A) Tyrosine B) Leucine C) Cystine D) Alanine
- Correct Answer: C
- Rationale: Hexagonal plate crystals in acidic urine are diagnostic for cystinuria, an inherited metabolic defect that impairs the renal reabsorption of cystine.
Q59. A semen analysis is performed to evaluate fertility. What is the minimum lower reference limit for progressive sperm motility within 1 hour of ejaculation, according to the current World Health Organization (WHO) standards? A) At least 32% progressive motility B) At least 75% progressive motility C) Exactly 100% motility D) Less than 10% motility
- Correct Answer: A
- Rationale: Current WHO reference criteria for semen analysis state that at least 32% of the spermatozoa should exhibit progressive motility (moving forward linearly or in large circles) to be classified as normal.
Q60. What condition or dietary factor can lead to a false-positive occult blood reaction on a urinalysis reagent strip? A) High dietary intake of Vitamin C (ascorbic acid) B) Presence of strong oxidizing contaminants or microbial peroxidases in the collection container C) Complete absence of red cells on microscopic view D) High specific gravity readings above 1.030
- Correct Answer: B
- Rationale: Reagent strips detect occult blood using the pseudoperoxidase activity of hemoglobin. Strong oxidizing agents like bleach or certain bacterial peroxidases can cause a false-positive color change in the absence of blood.
Part 7: Immunology and Serology
Q61. A patient presents with fever, joint pain, and a butterfly rash across her face. The physician suspects Systemic Lupus Erythematosus (SLE). Which serological screening test is most sensitive for supporting a diagnosis of SLE? A) Rheumatoid Factor (RF) assay B) Antinuclear Antibody (ANA) test C) Anti-Streptolysin O (ASO) titer ) Widal test Panel
- Correct Answer: B
- Rationale: The ANA test by indirect immunofluorescence has a sensitivity of over 95% for SLE, making it the standard initial screening tool, though positive results require confirmation with more specific antibodies like anti-dsDNA.
Q62. What type of immunological reaction principle forms the basis of the classic VDRL (Venereal Disease Research Laboratory) screening test for Syphilis? A) Direct hemagglutination B) Flocculation (precipitation of fine particles) C) Complement fixation cascade D) Chemiluminescent enzyme link
- Correct Answer: B
- Rationale: The VDRL test mixes patient serum with a cardiolipin-cholesterol-lecithin antigen suspension. If reagin antibodies are present, they bind the lipoidal antigen to form visible microscopic clumps, a reaction termed flocculation.
Q63. A patient serum sample is tested using the Widal agglutination test. A high titer of antibodies against the somatic “O” antigen (≥1:160) of Salmonella enterica serovar Typhi suggests: A) Chronic carrier status from a infection 10 years ago B) An active, acute phase infection of typhoid fever C) Successful previous vaccination with no disease D) A past infection that has fully resolved
- Correct Answer: B
- Rationale: In the Widal test, a significant elevation in titers against the lipopolysaccharide somatic “O” antigen indicates an active, acute infection because O antibodies appear early and disappear faster than flagellar “H” antibodies.
Q64. In western blot assays used as confirmatory testing platforms for HIV infection, what is the biological significance of bands appearing at positions p24, gp120, and gp41? A) They represent non-specific human cell line impurities B) They represent specific structural core (p24) and envelope (gp120, gp41) viral proteins of HIV C) They indicate the presence of active hepatitis co-infections D) They are artifacts caused by poor gel preparation
- Correct Answer: B
- Rationale: Western blotting separates HIV viral proteins by molecular weight. A positive validation requires detecting antibodies directed against specific viral structural antigens, typically including the core protein p24 and envelope glycoproteins gp41 or gp120/gp160.
Q65. Which class of immunoglobulin is produced first during a primary immune response following exposure to a novel foreign pathogen? A) Immunoglobulin G (IgG) B) Immunoglobulin A (IgA) C) Immunoglobulin M (IgM) D) Immunoglobulin E (IgE)
- Correct Answer: C
- Rationale: IgM is a pentameric antibody that serves as the primary antigen receptor on B cells and is the first immunoglobulin class secreted during an initial immune response before class-switching to IgG occurs.
Q66. A laboratory technologist runs a quantitative ELISA assay. During the final step, an enzyme labeled to an antibody reacts with a colorless substrate to produce a colored product. What is the common term for this substrate material? A) Conjugate buffer B) Chromogen C) Diluent matrix D) Adjuvant factor
- Correct Answer: B
- Rationale: A chromogen is a chemical substance that undergoes a color change when catalyzed by an enzyme (such as horseradish peroxidase), allowing for spectrophotometric quantification of target analytes in ELISA assays.
Q67. A patient with a sore throat is suspected of having a post-streptococcal sequela like rheumatic fever. Which serological test detects recent infections caused by Group A Beta-Hemolytic Streptococci? A) C-Reactive Protein (CRP) agglutination B) Anti-Streptolysin O (ASO) titer assay C) Heterophile antibody screening test D) Cold-agglutinin titration
- Correct Answer: B
- Rationale: Group A Streptococci produce the exotoxin Streptolysin O. Measuring elevated or rising titers of anti-streptolysin O (ASO) antibodies provides evidence of a recent or preceding streptococcal infection.
Q68. What type of hypersensitivity reaction is mediated by IgE antibodies binding to mast cells, triggering degranulation and histamine release within minutes of exposure to an allergen? A) Type I Immediate Hypersensitivity B) Type II Antibody-Dependent Cytotoxic Hypersensitivity C) Type III Immune Complex-Mediated Hypersensitivity D) Type IV Delayed-Type Cell-Mediated Hypersensitivity
- Correct Answer: A
- Rationale: Type I hypersensitivity (allergic/anaphylactic reactions) involves allergen cross-linking of IgE molecules bound to the surface of mast cells and basophils, causing rapid mediator release.
Q69. A laboratory introduces a new serological assay. The test correctly identifies 98 out of 100 individuals who truly do not have the target disease entity. This metric reflects the test’s: A) Clinical Sensitivity B) Diagnostic Specificity C) Positive Predictive Value D) Analytical Range
- Correct Answer: B
- Rationale: Diagnostic specificity is the ability of a test to correctly identify and yield a negative result for individuals who do not have the disease (True Negatives / [True Negatives + False Positives]).
Q70. In flow cytometry applications used to monitor HIV-positive patients, which cellular surface markers are targeted to quantify absolute helper T-lymphocyte concentrations? A) CD8 and CD3 markers B) CD4 and CD3 markers C) CD19 and CD20 markers D) CD56 and CD16 markers
- Correct Answer: B
- Rationale: Helper T-lymphocytes express both the CD3 marker (common to all T cells) and the CD4 coreceptor. Flow cytometry targets these surface proteins to monitor immune status in HIV-positive individuals.
Part 8: Histopathology and Cytology
Q71. A tissue biopsy is obtained from surgery. What is the standard concentration and composition of the most widely used routine chemical fixative in histopathology laboratories? A) 10% Neutral Buffered Formalin B) 100% Glacial Acetic Acid C) 70% Ethyl Alcohol D) 2% Mercuric Chloride solution
- Correct Answer: A
- Rationale: 10% neutral buffered formalin (equivalent to 4% formaldehyde solution) is the standard fixative because it preserves tissue structures by cross-linking proteins with minimal shrinkage or distortion.
Q72. During tissue processing, what is the correct operational sequence of steps required to prepare a fixed tissue specimen for paraffin wax embedding? A) Clearing → Dehydration → Infiltration B) Dehydration → Clearing → Infiltration (Embedding) C) Infiltration → Microtomy → Fixation D) Staining → Clearing → Grossing
- Correct Answer: B
- Rationale: Tissue processing follows a specific order: first, dehydration removes water using increasing concentrations of alcohol; next, clearing replaces the alcohol with a paraffin-miscible solvent like xylene; finally, infiltration fills the tissue spaces with molten paraffin wax.
Q73. A laboratory technician observes that ribboned sections cut on a rotary microtome show regular, alternating thick and thin variations, or chatter lines. What technical error causes this issue? A) The water bath temperature is too low B) The microtome knife or clearance angle is loose or set too steep C) The paraffin wax block is completely soft D) The tissue was fixed for too long
- Correct Answer: B
- Rationale: Mechanical vibration line errors (“chatter”) occur when the microtome blade or tissue block clamp is loose, or if a steep knife clearance angle causes the blade to vibrate against hard tissue during cutting.
Q74. In the standard Hematoxylin and Eosin (H&E) staining protocol, what is the role of hematoxylin, and what cellular structure does it target? A) It is an acidic dye that stains basic cytoplasmic structures pink B) It is a basic dye that acts with a mordant to stain acidic nuclear components (chromatin) blue/purple C) It is a clearing agent that dissolves lipids D) It is a counterstain that colors collagen fibers bright red
- Correct Answer: B
- Rationale: Hematoxylin functions as a basic dye when combined with a metal mordant. It binds to negatively charged, acidic cellular structures like nucleic acids in the nucleus, coloring them blue-purple.
Q75. Which chemical solvent is standardly used as a clearing agent during tissue processing and as a dewaxing/misclibility broker prior to mounting cover glasses? A) Ethanol B) Xylene C) Acetone D) Distilled water
- Correct Answer: B
- Rationale: Xylene is a clear aromatic hydrocarbon that is miscible with both absolute alcohol and paraffin wax, making it an excellent agent for clearing tissues during processing and removing wax before staining.
Q76. A cytotechnologist evaluates a cervical Papanicolaou (Pap) smear sample. Under microscopy, cells display marked nuclear enlargement, hyperchromasia, irregular nuclear membranes, and a high nuclear-to-cytoplasmic (N:C) ratio. These morphological changes indicate: A) Normal glycogen accumulation B) Cellular malignancy or severe dysplasia (Epithelial neoplasia) C) Artifacts due to air-drying delays D) Acute bacterial cytolysis
- Correct Answer: B
- Rationale: Enlarged, darkly stained nuclei (hyperchromasia) with irregular outlines and an increased N:C ratio are classic cytological hallmarks of dysplastic or malignant transformations.
Q77. What chemical fixative is standardly used for immediate wet-fixation of exfoliative cytology smears (such as Pap smears) to prevent air-drying artifacts and preserve nuclear detail? A) 95% Ethyl Alcohol (Ethanol) B) 10% Glutaraldehyde C) Liquid Chloroform D) 10% Picric acid
- Correct Answer: A
- Rationale: Cytological smears require rapid fixation to preserve fine nuclear details. 95% ethyl alcohol is the preferred wet-fixative for routine Pap and fine needle aspiration (FNA) smears.
Q78. During microtomy cutting operations, a histotechnologist notes that tissue ribbons are splitting vertically as they slide down the knife edge. This problem can be resolved by: A) Increasing the room temperature B) Cleaning the knife edge to remove any nicked spots or wax accumulation C) Re-fixing the tissue sample D) Using a water bath heated to 90°C
- Correct Answer: B
- Rationale: Vertical splits or lines in a paraffin ribbon are typically caused by a nick in the microtome blade edge or a hard particle (like calcium or grit) lodged on the knife path, requiring a shift to a clean blade section.
Q79. Which special stain is used in histopathology to identify glycogen deposits and confirm fungal structures by coloring them bright magenta? A) Masson’s Trichrome stain B) Periodic Acid-Schiff (PAS) stain C) Von Kossa stain D) Oil Red O stain
- Correct Answer: B
- Rationale: The PAS stain oxidizes tissue carbohydrates into aldehydes, which react with Schiff’s reagent to produce a magenta color. This technique is highly effective for visualizing glycogen, basement membranes, and fungal cell walls.
Q80. What is the fundamental operational difference between “Exfoliative Cytology” and “Fine Needle Aspiration Cytology (FNAC)” sampling methodologies? A) Exfoliative cytology is only performed on deceased patients B) Exfoliative cytology collects cells that have shed naturally or been scraped from epithelial surfaces, whereas FNAC uses a needle and syringe to actively extract cells from deep tissue masses C) FNAC requires a 5-day inpatient hospital stay ) Exfoliative cytology requires processing tissue into paraffin blocks
- Correct Answer: B
- Rationale: Exfoliative cytology evaluates cells naturally shed or brushed from surfaces (e.g., urine, sputum, Pap smears). FNAC is an interventional technique that uses a thin needle to aspirate cellular material from palpable or deep-seated tumors.
Part 9: Laboratory Management and Quality Assurance
Q81. A medical laboratory implements Westgard rules to monitor daily quality control charts. A single control value exceeds the mean by more than 3 standard deviations (13s). How should the technologist manage this run? A) Accept the run and report patient results since it is a minor warning B) Reject the run, hold patient results, and investigate the system for a random or severe systematic error C) Adjust the analyzer calibration settings manually until it fits inside 1 SD ) Wait until the next shift to retest the control sample
- Correct Answer: B
- Rationale: The 13s Westgard rule violation indicates a highly significant deviation that typically reflects a random error or the start of a major systematic shift, requiring rejection of the analytical run and corrective action.
Q82. According to standard biosafety practices, which containment level is required when handling high-risk, dangerous indigenous or exotic pathogens that can cause fatal airborne infections for which no vaccines or treatments exist? A) Biosafety Level 1 (BSL-1) B) Biosafety Level 2 (BSL-2) C) Biosafety Level 3 (BSL-3) D) Biosafety Level 4 (BSL-4)
- Correct Answer: D
- Rationale: BSL-4 facilities provide maximum containment and are reserved for dangerous, exotic agents (like Ebola or Marburg viruses) that pose a high risk of life-threatening, aerosol-transmitted laboratory infections for which protective therapies are unavailable.
Q83. A laboratory professional wants to assess the precision of a newly purchased automated hematology analyzer over a 30-day trial period. Which statistical index should be calculated? A) Mean value only B) Coefficient of Variation (CV) or Standard Deviation (SD) C) Diagnostic Sensitivity ratio D) Linear Regression slope
- Correct Answer: B
- Rationale: Precision refers to the reproducibility of a test method. It is statistically evaluated using the standard deviation (SD) and coefficient of variation (CV), where lower values signify greater precision.
Q84. What type of laboratory error occurs if a sample is collected from the wrong patient or mislabeled at a health center clinic ward prior to reaching the laboratory bench? A) Analytical error B) Pre-analytical error C) Post-analytical error D) Random instrument failure
- Correct Answer: B
- Rationale: Pre-analytical errors occur before the actual testing process begins. Examples include incorrect patient identification, faulty sample collection, improper preservation, and transit delays.
Q85. While reviewing a Levey-Jennings control chart, a laboratory supervisor notes that six consecutive control points have fallen on one side of the mean line, showing a steady directional trend. This pattern indicates: A) Excellent laboratory precision stability B) A systematic error or shift in the analytical system C) Random variations that cancel out over time D) An operator transcription error
- Correct Answer: B
- Rationale: A shift or consistent trend on a Levey-Jennings chart where consecutive points fall on one side of the mean indicates a systematic error, which can be caused by reagent degradation, instrument wear, or calibration shifts.
Q86. Which class of fire extinguisher should be installed near electrical analytical machinery inside a clinical laboratory to extinguish fires involving live electrical circuits safely? A) Class A extinguisher (Water-based) B) Class B extinguisher (Foam-based) C) Class C extinguisher (Carbon Dioxide or Dry Chemical non-conductive agent) D) Class D extinguisher (Combustible metal suppressant)
- Correct Answer: C
- Rationale: Class C fire extinguishers use non-conductive agents like carbon dioxide or dry chemicals, making them safe for electrical fires without damaging circuits or shocking the user.
Q87. What is the primary purpose of participating in an External Quality Assessment (EQA) or Proficiency Testing program? A) To lower the electricity costs of laboratory instruments B) To independently evaluate a laboratory’s testing accuracy by comparing its results with peer institutions using blind control samples C) To audit the financial records and tax compliance of the facility D) To shorten the working hours of laboratory staff
- Correct Answer: B
- Rationale: EQA programs distribute blind samples to participating laboratories. This allows facilities to compare their performance against peer laboratories and reference centers to detect long-term systematic errors and ensure accuracy.
Q88. A laboratory technologist accidentally spills a concentrated strong acid solution on the benchtop. What is the correct protocol for managing this chemical spill? A) Wipe it up immediately with a dry paper towel without wearing gloves B) Neutralize the acid using a weak base like sodium bicarbonate, then clean the area with water while wearing personal protective equipment (PPE) C) Pour concentrated sodium hydroxide directly onto the spill D) Dilute it by splashing water from a bucket
- Correct Answer: B
- Rationale: Acid spills should be managed by neutralizing the chemical with a weak base (such as sodium bicarbonate or a commercial neutralizing agent) while wearing appropriate PPE, followed by a thorough water rinse.
Q89. In a quality management system, what does the abbreviation “TAT” stand for, and why is it monitored as a key performance indicator? A) Total Analytical Temperature; ensures incubator consistency B) Turnaround Time; measures the total time elapsed from when a test is ordered or sample received to when results are reported C) Trans-Azide Titration; checks chemical purity indices D) Technical Assessment Team; tracks staff vacation schedules
- Correct Answer: B
- Rationale: Turnaround Time (TAT) is the interval between specimen registration and result verification. It is a key metric used to assess laboratory efficiency and the timeliness of service delivery.
Q90. What international document or standard outlines the specific requirements for quality and competence in medical laboratories? A) ISO 9001 B) ISO 15189 C) ISO 14001 D) ISO 17025
- Correct Answer: B
- Rationale: ISO 15189 is an international standard developed by the International Organization for Standardization that specifies the quality management system requirements unique to medical laboratories.
Part 10: Molecular Diagnostics and Special Techniques
Q91. What are the three consecutive temperature-dependent operational steps executed during a single cycle of a standard Polymerase Chain Reaction (PCR) assay? A) Infiltration → Embedding → Microtomy B) Denaturation → Annealing → Extension C) Transcription → Translation → Lysis D) Agglutination → Precipitation → Electrophoresis
- Correct Answer: B
- Rationale: A PCR cycle involves three main steps: denaturation (separating double-stranded DNA at high heat), annealing (binding primers to target sequences at lower temperatures), and extension (synthesizing new DNA strands using a heat-stable polymerase).
Q92. In molecular testing workflows, what primary function does the enzyme Reverse Transcriptase perform? A) It cuts double-stranded DNA molecules at specific restriction sites B) It synthesizes complementary DNA (cDNA) using a single-stranded RNA template C) It joins broken Okazaki fragments during replication D) It breaks down complex cellular protein chains
- Correct Answer: B
- Rationale: Reverse transcriptase is an RNA-dependent DNA polymerase that transcribes single-stranded RNA into complementary DNA (cDNA), an essential step for analyzing RNA viruses like HIV or Hepatitis C.
Q93. A molecular technician runs an agarose gel electrophoresis to separate amplified DNA pieces. Which direction does DNA migrate, and why? A) Toward the positive electrode (anode) because the phosphate backbone of DNA carries a net negative charge B) Toward the negative electrode (cathode) because DNA is highly alkaline C) It stays completely stationary at the loading well center D) It moves toward the light source due to phototaxis
- Correct Answer: A
- Rationale: The phosphate groups in the DNA backbone are negatively charged at neutral pH. During electrophoresis, this charge drives DNA fragments to migrate through the gel matrix toward the positive electrode (anode).
Q94. What is the distinct advantage of Real-Time PCR (quantitative PCR / qPCR) over traditional, end-point gel-based PCR assays? A) Real-time PCR takes 5 days longer to generate data B) It allows for the continuous monitoring and quantification of amplified DNA targets during the active reaction cycles using fluorescent dyes C) It eliminates the need for any thermal cycling machinery D) It works using dead bacterial organisms only
- Correct Answer: B
- Rationale: Real-time PCR incorporates fluorescent probes or dyes (like SYBR Green) to monitor the accumulation of amplified DNA during the reaction, enabling accurate quantification without post-PCR gel analysis.
Q95. Which technique uses specific fluorophore-labeled oligonucleotide probes to detect and localize specific DNA sequences directly within intact cellular or tissue chromosome preparations under a fluorescence microscope? A) Western Blotting B) Fluorescence In Situ Hybridization (FISH) C) Enzyme Immunoassay (EIA) D) Thin-Layer Chromatography
- Correct Answer: B
- Rationale: FISH is a cytogenetic technique that uses fluorescently labeled single-stranded DNA or RNA probes to hybridize with complementary target sequences within intact fixed cells or tissue specimens.
Q96. A molecular laboratory uses a clean-room workflow design divided into three separate zones: Reagent Preparation, Sample Processing, and Amplification/Detection. What is the purpose of this strict, one-way directional workflow? A) To minimize physical walking distance for laboratory staff B) To prevent carryover contamination of clean master-mix reagents with amplified DNA products (amplicons) C) To keep the instrument noise localized to one zone D) To lower the facility’s air conditioning bills
- Correct Answer: B
- Rationale: PCR is highly sensitive; even minute traces of amplified DNA can contaminate fresh reagents and produce false-positive results. A one-way workflow separating pre-amplification and post-amplification steps helps prevent this cross-contamination.
Q97. What heat-stable enzyme is isolated from the extremophile bacterium Thermus aquaticus and used in PCR assays to withstand repetitive high-temperature denaturation steps without losing function? A) RNA Polymerase II B) Taq DNA Polymerase C) Alkaline Phosphatase D) EcoRI Restriction Endonuclease
- Correct Answer: B
- Rationale: Taq polymerase is a heat-stable DNA polymerase that can survive the high temperatures (94∘C−95∘C) required to denature DNA strands during PCR, eliminating the need to add fresh enzyme after every cycle.
Q98. A technician runs an automated Sanger sequencing reaction to decode a gene. Which modified nucleotide component functions as an absolute chain terminator by lacking a 3′-hydroxyl group, preventing further phosphodiester bond formation? A) Deoxynucleoside triphosphates (dNTPs) B) Dideoxynucleoside triphosphates (ddNTPs) C) Ribonucleoside monophosphates D) Methylated purine bases
- Correct Answer: B
- Rationale: Sanger sequencing relies on dideoxynucleoside triphosphates (ddNTPs). Because ddNTPs lack the 3′-hydroxyl group required to bind the next nucleotide, their incorporation stops DNA chain elongation.
Q99. What molecular methodology uses an array of tiny microspots containing specific capture DNA sequences attached to a solid surface to monitor the expression levels of thousands of genes simultaneously? A) Northern Blotting strip B) DNA Microarray technology C) Isoelectric focusing lane D) Column Chromatography assay
- Correct Answer: B
- Rationale: DNA microarrays feature thousands of microscopic nucleic acid probes bound to a solid substrate, allowing researchers to analyze gene expression profiles or identify multiple genetic variations concurrently.
Q100. During a molecular test for viral load quantification, a internal control nucleic acid sequence is added directly into every patient sample test tube. If a patient sample shows no target viral signal and no internal control signal at the end of the run, how should the result be interpreted? A) Report the viral load as zero or completely negative B) Report the viral load as critically high C) The run is invalid due to amplification inhibition or extraction failure; the sample must be retested D) The analyzer needs an immediate hardware replacement
- Correct Answer: C
- Rationale: The internal control sequence must amplify successfully to prove the assay worked. If both the patient target and the internal control fail to show a signal, it indicates that the extraction step failed or that PCR inhibitors are present, making the test invalid.