ANSWERS

1. What are the advantages and disadvantages of glassware and plasticware in the laboratory?
   • Glass: Advantages - many sizes available, easy to clean, suitable for chemical and reagent storage, Pyrex is resilient to heat.
   • Glass: Disadvantages - shatters on breaking, relatively expensive.
   • Plastic: Advantages - durable and safe.
   • Plastic: Disadvantages - not heat-proof, can be difficult to clean thoroughly if scratched.
2. What is the difference between a graduated pipette and a one-mark volumetric pipette?
   A graduated pipette has a series of indicators of content volume, while a one-mark pipette has a single mark indicating a specific volume.
3. Describe the following pipettes: micro, automatic, Pasteur and Thoma.
   • Micro = A very small pipette with colour-coded disposable tips, may have a probe for positive displacement.
   • Automatic = A pipette which electronically dispenses a required volume of liquid one shot at a time, commonly used for ELISA plate work.
   • Pasteur = Traditionally made of soda glass with a fine point and a rubber bulb, plastic versions now commonly used.
   • Thoma = Haemocytometer dilution pipette, used with cell diluting fluid, contains a red bead for red blood cell counts and a white bead for white cell counts.
4. What is a pipette filler? Give an example.
   A syringe or mechanical device used to apply suction. An example is the Griffin, which comprises a rubber bulb with 3 valves.
5. What is meant by a reagent?
   A reagent is a substance employed to produce a chemical reaction.
6. Describe the following types of bottle used in laboratories: reagent, dropping, bijoux, McCartney, Winchester and universal.
   • Reagent = A fairly dumpy jar with a screw top or glass stopper; ideal for chemical storage as low centre of gravity means that it is not likely to be knocked over.
   • Dropping = A small bottle with a pipette incorporated into the lid; used for stains and indicators.
   • Bijoux = The smallest sized McCartney bottle (see below).
   • McCartney = A bottle with a narrow neck and aluminium screw cap; often used for samples.
   • Winchester = A tall amber glass bottle; very James Herriott! Largely superseded by a wider based type which is less likely to be knocked over.
7. Describe how you would clean laboratory glassware.
   • First clean in cold water to remove protein residues such as blood
   • Soak in an effective disinfectant at the correct dilution
   • Use a non-abrasive bristle brush to remove surface material
   • Soak again, or use an ultrasonic bath
   • Rinse in deionised water three times to remove any residual detergent
   • Drain on a suitable rack
   • Use a hot air oven to dry, or air dry in a clean environment
8. Upon what piece of laboratory equipment would you find a Vernier scale?
   The microscope.
9. What is the Vernier scale?
   A position finding device for the microscope. It comprises 2 scales: North & South and East & West. When a point of interest is found, readings of both scales are taken, the Verniers are recorded and the position of the slide label noted. The scales and Verniers can then be pre-set to relocate the point of interest at a later time.
10. What is the function of the substage condenser on a microscope?
    The substage condenser focuses an image of the light source upon the object.
11. What is the function of the iris diaphragm on a microscope?
    The iris diaphragm is an aperture that modifies the amount of light reaching the object.
12. Which magnification is used for viewing under oil immersion?
    The high power (100 x) objective lens is used for viewing under oil immersion.
13. How may the bulb life of the microscope be maximised?
    The rheostat should be turned down before switching off, or if the light is left on whilst the microscope is not in use.
14. What is meant by "racking up"?
    Before viewing an object under the microscope, the lowest magnification objective lens is chosen, and the coarse focus is used to bring the stage up to the object so that it is as close as possible to the objective lens without touching it. When the microscope is used for viewing, the coarse focus is used to slowly bring down the stage until the object is visible. This technique ensures that the operator does not damage the objective lens with the stage.
15. What is a colorimeter?
    An instrument used for biochemistry that measures the intensity of the colour of a solution by passing a light of a known wavelength through the solution and measuring the absorbency of the light. Inverse calorimetry measures the light absorbed, whilst direct calorimetry measures the light transmitted.
16. When might a Bunsen burner be used in the laboratory?
    For heat fixing bacterial smears.
17. What is a centrifuge?
    A machine that spins at speed to produce a high gravitational force for the separation of blood samples and other fluids into solid and liquid phases.
18. What is a microhaematocrit centrifuge?
    A type of centrifuge which separates whole blood in capillary tubes to enable packed cell volume (PCV) measurement. It has a special rotor with an almost flat horizontal surface and holding slots for the capillary tubes.
19. What precautions must be taken when using the centrifuge?
    • Always operate on a firm, flat surface.
    • The machine must be balanced.
    • Never pressure the shaft to try to slow the machine down.
20. Describe the cleaning and maintenance of the centrifuge.
    • Keep a maintenance log book.
    • Use xylene and a soft cloth to wipe over the surface.
    • Remove buckets or haematocrit attachment prior to cleaning.
    • Replace the motor brushes when worn.
    • Lubricate according to the manufacturer's instructions.
21. What is a laboratory incubator used for?
    To culture bacteria in a well-insulated environment at a constant temperature (usually 37°C which is the optimum for almost all pathogenic bacteria).
22. Describe the cleaning and maintenance of the incubator.
    • Don protective clothing.
    • Refer to the manufacturer's instructions and take special care due to the risk from potentially harmful bacteria.
    • Check the wiring and thermostat regularly.
    • Maintain a daily record of the temperature.
    • Following use, clean well with an effective disinfectant and fumigate.
    • Keep records of servicing.