BACE - Biotechnician Assistant Credentialing Basic Laboratory Equipment Use Questions and Answers 1 — Questions and Answers
Question 1: A technician needs to accurately transfer 185 µL of a buffer solution. The lab has P20, P200, and P1000 micropipettes available. Which micropipette should be used for the highest accuracy and precision?
- P1000
- P20
- Any of them will work equally well
- P200 (Correct answer)
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 2: Before starting a microcentrifuge, a technician places two 1.5 mL tubes containing samples of unequal mass opposite each other in the rotor. What is the most likely consequence of this action?
- The samples will not pellet correctly.
- The centrifuge will generate excessive noise and vibration, potentially damaging the unit. (Correct answer)
- The centrifuge lid will not lock properly.
- The run time will automatically increase to compensate.
Correct answer: The centrifuge will generate excessive noise and vibration, potentially damaging the unit.
Centrifuges must be properly balanced by mass to operate safely and effectively. Placing tubes with unequal masses opposite each other creates an imbalance. At high rotational speeds, this imbalance causes significant vibration, which can damage the motor and rotor, posing a serious safety risk.
Question 3: A biotechnician is preparing to measure the pH of a critical buffer solution. Which of the following is the most important first step to ensure an accurate reading?
- Wiping the electrode dry with a paper towel after rinsing.
- Ensuring the buffer solution is at exactly 25°C.
- Calibrating the meter using at least two standard buffers of known pH. (Correct answer)
- Rinsing the electrode with the buffer solution to be measured.
Correct answer: Calibrating the meter using at least two standard buffers of known pH.
Before use, a pH meter must be calibrated against standard solutions of known pH (e.g., pH 4.0, 7.0, 10.0). This process adjusts the meter's response to match the known pH values of the standards, ensuring that subsequent measurements of unknown samples are accurate. While other steps are part of good practice, calibration is the prerequisite for accuracy.
Question 4: What are the three critical parameters that an autoclave utilizes to achieve sterilization of laboratory equipment and media?
- High temperature, high pressure, and steam. (Correct answer)
- UV radiation, high pressure, and filtration.
- Dry heat, long duration, and vacuum.
- 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 5: 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 calibrate the instrument by setting the absorbance of the solvent to zero. (Correct answer)
- To verify that the correct wavelength has been selected.
- To set the maximum absorbance reading (100%) for the instrument.
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 6: A protocol requires a 15-minute incubation of an enzymatic reaction at exactly 37°C. Which of the following is the most critical step when using a standard laboratory water bath for this procedure?
- Using a lid on the water bath to prevent evaporation.
- Adding a stir bar to the reaction tube to ensure even heating.
- Placing the tube in the bath immediately after turning the power on.
- Ensuring the water level is high enough to cover the portion of the tube containing the reaction mixture. (Correct answer)
Correct answer: Ensuring the water level is high enough to cover the portion of the tube containing the reaction mixture.
For effective and uniform heat transfer, the reaction mixture inside the tube must be fully submerged below the water level in the bath. If the sample liquid is above the water level, it will not be heated to the target temperature, leading to inaccurate results. While using a lid and preheating the bath are good practices, ensuring the sample is submerged is most critical for the incubation itself.
BACE - Biotechnician Assistant Credentialing Basic Laboratory Equipment Use Questions and Answers 1
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?