STP Technical Skills & Application 2

Question 1

When calibrating a spectrophotometer, which solution should be used to set the 100% transmittance (zero absorbance) baseline?

Accepted Answer

A blank reagent solution

Answer

A blank reagent solution (containing all reagents except the analyte) is used to zero the instrument, accounting for any absorbance from the reagents themselves.

Question 2

In a laboratory performing PCR, a technician observes amplification in the no-template control (NTC). What is the most likely cause?

Accepted Answer

Contamination of reagents or workspace with DNA

Answer

A positive NTC result indicates DNA contamination of reagents or the workspace, as no template was added to that reaction.

Question 3

Which statistical measure is most appropriate for describing the spread of a skewed dataset in a clinical laboratory context?

Accepted Answer

Interquartile range (IQR)

Answer

The IQR is preferred for skewed distributions because it is not influenced by extreme outliers, unlike standard deviation.

Question 4

A scientist needs to prepare 500 mL of a 0.1 M NaCl solution (MW = 58.44 g/mol). How many grams of NaCl are required?

Accepted Answer

2.92 g

Answer

Moles needed = 0.1 mol/L × 0.5 L = 0.05 mol; mass = 0.05 × 58.44 = 2.92 g.

Question 5

In Western blotting, what is the primary purpose of the blocking step?

Accepted Answer

To prevent non-specific antibody binding to the membrane

Answer

Blocking (e.g., with milk or BSA) saturates non-specific binding sites on the membrane so that antibodies only bind the target protein.

(STP) Scientist Training Programme Practice Test

(STP) Scientist Training Programme Practice Test

STP Technical Skills & Application 2