Practice Test 2 - Pre-Analytical Procedures Flashcards
Which glassware is used to measure 24-hour urine volume?
a) Beaker
b) Erlenmeyer Flask
c) Graduated cylinder
d) Volumetric flask
c) Graduated cylinder
Graduated cylinders are used to measure 24-hour urine volumes because they are designed to make accurate measurements of large volumes of liquids. They typically come in three sizes (500 mL, 1000 mL, and 2000 mL) and can measure in 5 mL, 10 mL or 20 mL increments.
Erlenmeyer flasks and beakers are used for mixing and transporting liquids. They are not used for making accurate measurements.
Volumetric flasks are used to measure very precisely one specific volume of liquid (100 mL, 250 mL, etc., depending on which flask you use). They cannot be used to measure unknown volume of liquid, such as a 24-hour urine sample.
A laboratory has an autoclave rule stating “Do not fill containers more than half full with liquids”. If a lab technician has to prepare 220ml of media for autoclaving, then which of these volume containers would be most appropriate?
a) 100 mL
b) 300 mL
c) 400 mL
d) 500 mL
d) 500 mL
2 X 220 mL = 440 mL.
This means only 500 mL container can contain 220 mL without becoming more than half-full.
Buffered commercial formalin is approximately ______ formaldehyde gas by weight/volume.
a) 4%
b) 10%
c) 40%
d) 70%
b) 10%
Buffered commercial formalin is typically a 10% solution of formaldehyde gas by weight/volume. This means that for every 100 millilitres of buffered formalin, there are 10 grams of formaldehyde gas present. The remaining volume is made up of water and a buffering agent.
Which clearing agent does NOT make tissues transparent/translucent?
a) Benzene
b) Cedarwood oil
c) Chloroform
d) Xylene
c) Chloroform
Tissues placed in chloroform do not become translucent.
Why do clearing agents need to be miscible with alcohol?
a) So they can dehydrate tissues completely
b) So they can remove dehydrating agents from tissues
c) To prevent damage to the clearing agent
d) To prevent damage to the tissue
b) So they can remove dehydrating agents from tissues
Clearing agents should be miscible (mixable) with alcohol to promote the rapid removal of the dehydrating agent from the tissue.
What happens if tissue is left in xylene for more than three hours?
a) The tissue becomes a milky colour
b) The tissue becomes brittle
c) The tissue becomes red
d) The tissue swells in size
b) The tissue becomes brittle
Xylene is a common solvent used in histology to remove thee water from tissue samples, making them more transparent and allowing for easier processing and embedding in paraffin wax. However, if tissue is left in xylene for too long, the tissue can become over-dehydrated and brittle.
What is the purpose of tissue filtration?
a) To give structural support to the tissue
b) Too keep the cells alive
c) To rehydrate the tissue
d) To remove bacteria from the tissue
a) To give structural support to the tissue
The role of the infiltration agent is to remove the clearing agent from the tissue and to completely permeate the tissue with paraffin wax. This will allow the tissue to harden and produce a wax block from which thin histological sections can be cut.
Infiltration is the:
a) permeation of the tissue with ethanol
b) permeation of the tissue with wax
c) removal of calcium from tissue
d) removal of water from tissue
b) permeation of the tissue with wax
Which freezing technique is the coldest?
a) Aerosol sprays
b) Carbon dioxide gas
c) Carbon dioxide ‘cardice’
d) Liquefied nitrogen
d) Liquefied nitrogen
Nitrogen is a liquid at around -195.8°C, making liquid nitrogen the coldest freezing technique.
What is the most common type of microtome in laboratories?
a) Cryostat
b) Rotary microtome
c) Sledge microtome
d) Ultramicrotome
b) Rotary microtome
The rotary microtome is a device that uses a motor to rotate the specimen and a knife to cut thin slices of the tissue sample. This type of microtome is preferred because it can produce thin and uniform sections of tissue, and it is relatively easy to use.
Which Gram stain reagent acts as a mordant to bind the stain to the bacteria?
a) Acetone
b) Ethanol
c) Iodine
d) Safranin
c) Iodine
Out of the four basic reagents used in Gram staining - crystal violet, iodine, ethanol or acetone, and safranin - iit is iodine that acts as a mordant that binds the stain to the bacteria.
Ethanol and acetone are wrong answers as these are the decolourizing agents.
Safranin is the wrong answer as this is the counter-stain.
Which element does Perls Prussian blue detect?
a) Iron
b) Lead
c) Mercury
d) Potassium
a) Iron
Perls Prussian blue colours iron blue, making it easily visible.
Amyloid staining uses which red dye?
a) Biebrich scarlet
b) Congo red
c) Eosin
d) Xylidine ponceau
b) Congo red
When a smear is too red, neutrophil graranules look:
a) blue-red
b) brilliant red
c) indistinct
d) light blue
b) brilliant red
Neutrophil granules normally stain pink or red. If too much red dye is used, the rarndules appear bright bred.
Which of these could cause stain precipitate when performing a stain?
a) Excessive humidity in the air
b) The staining procedure was too short
c) Too much buffer
d) Use of aged staining solutions
d) Use of aged staining solutions
Stain precipitate usually results from the use of aged staining solutions and inadequate rinsing of slides following the application of the stain.
What is the correct order of reagents used for Gram staining?
a) Crystal violet, iodine, acetone-alcohol, safranin
b) Crystal violet, safranin, acetone-alcohol, iodine
c) Iodine, crystal violet, acetone-alcohol, safranin
d) Safranin, iodine, crystal violet, acetone-alcohol
a) Crystal violet, iodine, acetone-alcohol, safranin
First, crystal violet is used to dye all the bacteria blue-purple. Then, Gram’s iodine is used to fix the dye to the bacteria, preventing the dye from being easily removed from the bacteria. After this, a decolourizing agent is used to remove the crystal violet dye from the gram-negative bacteria, leaving the gram-negative bacteria colourless. Finally, safranin is added to dye the gram-negative bacteria pink-red. The final result is that the gram-negative bacteria appear pink-red and the gram-positive bacteria appear blue-purple.
