Freshly poured paraffin blocks are cooled quickly on a cold plate because slow cooling:

Forms coarse crystals, so blocks crumble

Softens the tissue within the block

Raises the melting point of the wax

Traps air bubbles inside the tissue

While an appendix block is cut with a new blade on a rotary microtome, the ribbon curves steadily to one side. Which correction is right?

Trim the top and bottom block edges parallel

Increase the clearance angle to about 15°

Re-embed the tissue in softer wax

Lower the flotation bath temperature

In a closed (fluid-transfer) automatic tissue processor:

Tissue stays in one chamber; reagents are pumped in turn

Baskets of cassettes move between open beakers

Only one reagent is used for the whole schedule

Tissue passes through wax before the alcohols

Histotechnology: tissue processing and embedding

18 Kerala PSC Lab Technician Gr II practice questions on Histotechnology: tissue processing and embedding, part of Pathology. The first 18 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Freshly poured paraffin blocks are cooled quickly on a cold plate because slow cooling:
1. ASoftens the tissue within the block
2. BForms coarse crystals, so blocks crumble
3. CRaises the melting point of the wax
4. DTraps air bubbles inside the tissue
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Answer: B · Forms coarse crystals, so blocks crumble
When molten paraffin cools quickly it sets with a fine, even crystal structure that cuts smoothly into ribbons. Slow cooling lets large crystals grow, so the block is crumbly and cuts poorly. The tissue is oriented in the mould on the hot plate and the mould is then moved straight to the cold plate. Air bubbles come from careless pouring, not from the cooling rate.
- A: Slow cooling does not soften the tissue itself.
- C: The melting point is a property of the wax and does not change with cooling rate.
- D: Air bubbles come from careless pouring or poor impregnation, not slow cooling.
Question 2 · Easy
Which clearing agent does NOT make tissue transparent?
1. AChloroform
2. BCedarwood oil
3. CXylene
4. DToluene
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Answer: A · Chloroform
Most clearing agents have a refractive index close to that of tissue proteins, so the tissue turns translucent when the alcohol has been fully replaced. Chloroform removes alcohol and mixes with wax, but it does not make tissue transparent, so the end of clearing cannot be judged by eye. It is also slow and toxic. Xylene is the routine clearing agent, but long exposure makes tissue brittle.
- B: Cedarwood oil makes tissue transparent, although it is slow.
- C: Xylene makes tissue transparent within hours and is the routine choice.
- D: Toluene behaves like xylene and also makes tissue transparent.
Question 3 · Easy
Vacuum impregnation with paraffin wax is especially useful for which tissue?
1. ALiver
2. BLung
3. CKidney
4. DSpleen
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Answer: B · Lung
Lung contains air in its alveoli, which blocks the entry of wax and makes the tissue float. Under reduced pressure the trapped air and any remaining clearing agent are drawn out, so wax enters quickly and completely. Vacuum also shortens impregnation time for dense tissues, which limits their exposure to heat. Modern enclosed processors apply vacuum at every wax station.
- A: Liver is solid and impregnates well without vacuum.
- C: Kidney has no air spaces that need to be drawn out.
- D: Spleen is a solid, blood-rich organ without trapped air.
Question 4 · Hard
While an appendix block is cut with a new blade on a rotary microtome, the ribbon curves steadily to one side. Which correction is right?
1. ATrim the top and bottom block edges parallel
2. BIncrease the clearance angle to about 15°
3. CRe-embed the tissue in softer wax
4. DLower the flotation bath temperature
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Answer: A · Trim the top and bottom block edges parallel
A ribbon forms because the top edge of each section sticks to the bottom edge of the one before. If the top and bottom edges of the block are not parallel to each other and to the knife, every section is wedge-shaped and the ribbon curves. The other causes are a knife dull along one part, which a new blade rules out, or wax that is softer on one side. Trimming the block square and setting its edges parallel to the knife corrects it.
- B: The clearance angle affects compression and chatter, not the curve of the ribbon.
- C: Softer wax makes sections compress; it does not curve the ribbon.
- D: The flotation bath acts after cutting and cannot change the ribbon's shape.
Question 5 · Medium
In a closed (fluid-transfer) automatic tissue processor:
1. ABaskets of cassettes move between open beakers
2. BTissue stays in one chamber; reagents are pumped in turn
3. COnly one reagent is used for the whole schedule
4. DTissue passes through wax before the alcohols
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Answer: B · Tissue stays in one chamber; reagents are pumped in turn
In an enclosed processor the cassettes stay in a sealed retort while each reagent is pumped in, held and drained in sequence. Heat, vacuum, pressure and agitation can be applied, and fumes and spills stay contained. In the older carousel (tissue-transfer) type, baskets are moved between open beakers, which gives off more fumes. The order is the same in both: fixative, alcohols, clearing agent and wax.
- A: Moving baskets between open beakers describes the carousel (tissue-transfer) processor.
- C: Every schedule still runs fixative, alcohols, clearing agent and wax.
- D: Wax impregnation always comes last, after dehydration and clearing.
Question 6 · Easy
Paraffin wax for routine embedding usually has a melting point of about:
1. A37-40 °C
2. B56-58 °C
3. C70-72 °C
4. D45-48 °C
Answer and explanation in LearnFree account
Question 7 · Hard
On a processor whose wax baths have not been changed for weeks, many blocks are soft, the tissue crumbles out of the wax, and the wax smells of xylene. The most likely cause is:
1. AWax bath overheated to 70 °C
2. BTissue overfixed in buffered formalin
3. CWax contaminated by carried-over xylene
4. DBlocks cooled too quickly on a cold plate
Answer and explanation in LearnFree account
Question 8 · Medium
Tissue is dehydrated through graded alcohols (70%, 90%, then absolute) rather than placed straight into absolute alcohol. Why?
1. ATo fix the tissue a second time
2. BTo make the tissue transparent
3. CTo decalcify small bone pieces
4. DTo avoid shrinkage and distortion
Answer and explanation in LearnFree account
Question 9 · Medium
Why must tissue pass through a clearing agent such as xylene before wax impregnation?
1. AXylene stains tissue for orientation
2. BAlcohol does not mix with molten wax
3. CXylene removes formalin pigment
4. DXylene hardens tissue for cutting
Answer and explanation in LearnFree account
Question 10 · Easy
Two L-shaped brass pieces set on a glass or metal plate to form an adjustable embedding mould are called:
1. ALeuckart's pieces
2. BPeel-away moulds
3. CDisposable base moulds
4. DPaper boats
Answer and explanation in LearnFree account
Question 11 · Hard
A batch of small endoscopic biopsies was processed by mistake on the long overnight schedule used for large specimens. The sections are most likely to be:
1. AUnfixed and autolysed
2. BHard, brittle and cracked
3. CSoft and mushy in the centre
4. DCovered in formalin pigment
Answer and explanation in LearnFree account
Question 12 · Medium
When a skin biopsy is embedded, it is oriented in the mould so that sections:
1. AShow only the epidermis
2. BRun parallel to the skin surface
3. CPass vertically through all layers
4. DShow only the deep dermis
Answer and explanation in LearnFree account
Question 13 · Hard
After rough trimming, a gastric biopsy block shows only part of the tissue. A full face appears only after much trimming, and little tissue is left for levels. What was the most likely fault?
1. AToo little fixation time
2. BClearing agent left too long
3. CWax temperature too low in processing
4. DTissue not pressed flat in the mould
Answer and explanation in LearnFree account
Question 14 · Medium
Why is the paraffin wax oven kept only about 2-3 °C above the melting point of the wax?
1. AOverheating turns the wax yellow
2. BHigher heat makes wax set too slowly
3. CHigher heat dissolves the tissue fat
4. DOverheating makes tissue hard and brittle
Answer and explanation in LearnFree account
Question 15 · Medium
During clearing, a piece of tissue turns milky white in xylene instead of becoming transparent. This means that:
1. AThe tissue is over-fixed
2. BThe xylene is too fresh
3. CThe tissue is too thin
4. DDehydration was incomplete
Answer and explanation in LearnFree account
Question 16 · Easy
Anhydrous copper sulphate kept at the bottom of an absolute alcohol jar turns blue when:
1. AXylene has entered the jar
2. BWax has entered the jar
3. CThe alcohol is fully pure
4. DThe alcohol contains water
Answer and explanation in LearnFree account
Question 17 · Easy
What is the correct order of the main steps in paraffin tissue processing?
1. AFixation, clearing, dehydration, impregnation
2. BDehydration, fixation, clearing, impregnation
3. CFixation, impregnation, dehydration, clearing
4. DFixation, dehydration, clearing, impregnation
Answer and explanation in LearnFree account
Question 18 · Easy
Which dehydrating agent is most commonly used in routine tissue processing?
1. AEthyl alcohol
2. BAcetone
3. CDioxane
4. DGlycerol
Answer and explanation in LearnFree account

Histotechnology: tissue processing and embedding

Freshly poured paraffin blocks are cooled quickly on a cold plate because slow cooling:

Which clearing agent does NOT make tissue transparent?

Vacuum impregnation with paraffin wax is especially useful for which tissue?

While an appendix block is cut with a new blade on a rotary microtome, the ribbon curves steadily to one side. Which correction is right?

In a closed (fluid-transfer) automatic tissue processor:

Paraffin wax for routine embedding usually has a melting point of about:

On a processor whose wax baths have not been changed for weeks, many blocks are soft, the tissue crumbles out of the wax, and the wax smells of xylene. The most likely cause is:

Tissue is dehydrated through graded alcohols (70%, 90%, then absolute) rather than placed straight into absolute alcohol. Why?

Why must tissue pass through a clearing agent such as xylene before wax impregnation?

Two L-shaped brass pieces set on a glass or metal plate to form an adjustable embedding mould are called:

A batch of small endoscopic biopsies was processed by mistake on the long overnight schedule used for large specimens. The sections are most likely to be:

When a skin biopsy is embedded, it is oriented in the mould so that sections:

After rough trimming, a gastric biopsy block shows only part of the tissue. A full face appears only after much trimming, and little tissue is left for levels. What was the most likely fault?

Why is the paraffin wax oven kept only about 2-3 °C above the melting point of the wax?

During clearing, a piece of tissue turns milky white in xylene instead of becoming transparent. This means that:

Anhydrous copper sulphate kept at the bottom of an absolute alcohol jar turns blue when:

What is the correct order of the main steps in paraffin tissue processing?

Which dehydrating agent is most commonly used in routine tissue processing?