STP Technical Skills & Application 5

Question 1

Which term describes the ability of an analytical method to measure only the intended analyte without interference from other substances?

Accepted Answer

Analytical specificity (selectivity)

Answer

Analytical specificity (or selectivity) is the ability of an assay to measure the target analyte alone, even in the presence of other potentially interfering compounds.

Question 2

A laboratory scientist uses a haemocytometer to count cells. Under ×10 objective with a 10× eyepiece, the scientist counts 60 cells in a 1 mm² area at a depth of 0.1 mm. What is the cell concentration per mL?

Accepted Answer

6 × 10⁵ cells/mL

Answer

Volume counted = 1 mm² × 0.1 mm = 0.1 mm³ = 1×10⁻⁴ mL; concentration = 60 / 1×10⁻⁴ = 6×10⁵ cells/mL.

Question 3

In gel electrophoresis, what is the purpose of loading a DNA ladder alongside experimental samples?

Accepted Answer

To serve as a molecular weight reference for estimating fragment sizes

Answer

The ladder contains DNA fragments of known sizes that migrate predictably, allowing the sizes of experimental bands to be estimated by comparison.

Question 4

Which biosafety level (BSL) is required for work with Mycobacterium tuberculosis?

Accepted Answer

BSL-3

Answer

M. tuberculosis is a BSL-3 pathogen because it can cause serious or potentially lethal disease and is transmissible via aerosol, requiring respiratory protection and negative-pressure rooms.

Question 5

When using reverse transcription PCR (RT-PCR) to detect an RNA virus, what is the first enzymatic step?

Accepted Answer

Reverse transcriptase converts viral RNA into complementary DNA (cDNA)

Answer

Reverse transcriptase uses the viral RNA as a template to synthesise cDNA, which then serves as the template for conventional PCR amplification.

(STP) Scientist Training Programme Practice Test

(STP) Scientist Training Programme Practice Test

STP Technical Skills & Application 5