HT Microtomy & Staining 3 — Questions and Answers
Question 1: Which type of knife is most commonly used for routine paraffin sections on a rotary microtome?
- Wedge knife
- Plano-concave knife
- Disposable low-profile blade (Correct answer)
- Sledge knife
Correct answer: Disposable low-profile blade
Disposable low-profile blades are standard for routine rotary microtomy due to consistency and convenience.
Question 2: A Grocott's methenamine silver (GMS) stain is used primarily to demonstrate which organisms?
- Acid-fast bacteria
- Fungi and Pneumocystis jirovecii (Correct answer)
- Gram-positive cocci
- Spirochetes
Correct answer: Fungi and Pneumocystis jirovecii
GMS stain blackens the cell walls of fungi and Pneumocystis jirovecii against a green counterstain background.
Question 3: What is the function of the mordant in hematoxylin staining?
- To oxidize hematoxylin to hematein
- To link the dye to tissue components (Correct answer)
- To differentiate background staining
- To prevent overstaining
Correct answer: To link the dye to tissue components
A mordant (typically alum) forms a bridge between the hematein dye and tissue components, allowing dye binding.
Question 4: 'Wrinkles' or folds in paraffin sections are best corrected by:
- Increasing oven temperature
- Floating sections on a warm water bath (Correct answer)
- Re-embedding the block
- Using a sharper knife angle
Correct answer: Floating sections on a warm water bath
Floating sections on a 40-45°C water bath allows them to spread flat before mounting on a slide.
Question 5: The Ziehl-Neelsen stain differentiates acid-fast organisms from background using which reagent?
- Lugol's iodine
- Acid-alcohol decolorizer (Correct answer)
- Potassium permanganate
- Silver nitrate
Correct answer: Acid-alcohol decolorizer
Acid-alcohol decolorization removes carbol fuchsin from non-acid-fast background while acid-fast organisms retain the stain.
Question 6: Which embedding medium is best suited for enzyme histochemistry studies?
- Paraffin wax
- Celloidin
- Optimal cutting temperature (OCT) compound (Correct answer)
- Epoxy resin
Correct answer: Optimal cutting temperature (OCT) compound
OCT compound supports frozen sectioning without heat processing that would inactivate tissue enzymes.
Question 7: Section compression during microtomy is most effectively reduced by:
- Increasing block temperature
- Using a steeper knife angle
- Reducing cutting speed (Correct answer)
- Soaking the block in ice water
Correct answer: Reducing cutting speed
Slowing the cutting speed reduces mechanical compression of the tissue block during sectioning.
HT Microtomy & Staining 3
Which type of knife is most commonly used for routine paraffin sections on a rotary microtome?