MLS Laboratory Equipment & Techniques 2 — Questions and Answers
Question 1: Which centrifuge type uses a fixed angle rotor where tubes are held at a constant angle during spinning?
- Swinging-bucket centrifuge
- Fixed-angle centrifuge (Correct answer)
- Ultracentrifuge
- Microcentrifuge
Correct answer: Fixed-angle centrifuge
Fixed-angle rotors hold tubes at a set angle (typically 25–45°) throughout the run, causing particles to sediment along the tube wall.
Question 2: When calibrating a spectrophotometer, which solution is used to set 100% transmittance (zero absorbance)?
- Distilled water only
- The blank (reagent blank) (Correct answer)
- A standard of known concentration
- A positive control
Correct answer: The blank (reagent blank)
The reagent blank contains all reagents except the analyte and is used to zero the instrument, correcting for reagent color and background absorbance.
Question 3: A laboratory thermometer reads 37.2°C when placed in a 37.0°C reference bath. This difference is best described as:
- Random error
- Systematic error (bias) (Correct answer)
- Precision failure
- Analytical sensitivity issue
Correct answer: Systematic error (bias)
A consistent offset from the true value in one direction is systematic error (bias), which can often be corrected by calibration.
Question 4: Which pipette type is designed to deliver a single fixed volume and is NOT adjustable?
- Micropipette (adjustable)
- Serological pipette
- Volumetric (transfer) pipette (Correct answer)
- Pasteur pipette
Correct answer: Volumetric (transfer) pipette
Volumetric (transfer) pipettes are calibrated to deliver one precise fixed volume and offer the highest accuracy for that volume.
Question 5: In a biosafety cabinet Class II Type A2, the percentage of air recirculated within the cabinet versus exhausted is approximately:
- 100% recirculated, 0% exhausted
- 70% recirculated, 30% exhausted (Correct answer)
- 30% recirculated, 70% exhausted
- 50% recirculated, 50% exhausted
Correct answer: 70% recirculated, 30% exhausted
Class II Type A2 BSCs recirculate approximately 70% of air through HEPA filters and exhaust about 30% to the environment (via HEPA or hard-duct).
Question 6: What does the term 'resolution' refer to when describing a centrifuge's performance?
- Maximum RPM achievable
- Ability to separate two particles of different sedimentation rates (Correct answer)
- Temperature control accuracy
- Volume capacity of the rotor
Correct answer: Ability to separate two particles of different sedimentation rates
Resolution in centrifugation refers to how well the instrument can separate two populations of particles with different densities or sizes.
Question 7: A Neubauer hemocytometer counting chamber has a depth of:
- 0.01 mm
- 0.1 mm (Correct answer)
- 1.0 mm
- 0.5 mm
Correct answer: 0.1 mm
The standard Neubauer hemocytometer has a chamber depth of 0.1 mm, which is used in calculating cell counts per volume.
MLS Laboratory Equipment & Techniques 2
Which centrifuge type uses a fixed angle rotor where tubes are held at a constant angle during spinning?