STP Biomedical Sciences 2

Question 1

Which type of cell junction prevents the passage of molecules between adjacent epithelial cells?

Accepted Answer

Tight junction

Answer

Tight junctions (zonula occludens) form a seal between epithelial cells, preventing paracellular passage of molecules.

Question 2

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

Accepted Answer

To prevent non-specific antibody binding

Answer

Blocking with BSA or milk saturates non-specific binding sites on the membrane to reduce background signal.

Question 3

Which complement pathway is activated by mannose-binding lectin (MBL)?

Accepted Answer

Lectin pathway

Answer

MBL recognizes carbohydrate patterns on pathogens and activates complement via the lectin (MBL) pathway.

Question 4

A patient has a prolonged aPTT but normal PT. Which factor is most likely deficient?

Accepted Answer

Factor VIII

Answer

Factor VIII deficiency (hemophilia A) prolongs aPTT (intrinsic pathway) while PT (extrinsic pathway) remains normal.

Question 5

Which microscopy technique is best suited for imaging live, unstained cells without phototoxicity concerns?

Accepted Answer

Phase contrast microscopy

Answer

Phase contrast microscopy exploits differences in refractive index and requires no staining or fixation, making it ideal for live cells.

(STP) Scientist Training Programme Practice Test