2.1.1 B) Preparation and Examination of Microscope Slides for Use in Light Microscopy

Question 1

What is reason for calibrating the eyepiece graticule and stage micrometer?

Answer 1

to measure the size of the specimen

Question 1

How do you prepare a microscope slide to view specimens in a light microscope? (wet mount)

Answer 1

• Pipette a drop of water onto a microscope slide
• Use tweezers to place specimen on top of water droplet (this needs to be just a thin layer of cells so that light can pass through).
• Add a drop of stain e.g. oesin stains the cell’s cytoplasm - this creates contrast and enables
  organelles to be visualised
• Add a cover slip to protect the specimen by first standing the slip upright on the slide then carefully tilting and lowering down, taking care
  not to trap any air bubbles (as they would obstruct the view of the specimen)

Question 2

How do you calibrate a microscope?

Answer 2

• Place the stage micrometer on the stage and focus the lens so that you can clearly see the divisions
• Align the eyepiece graticule with the stage micrometer
• Each division of the stage micrometer is 0.1 mm - if the eyepiece graticule spans a total of three divisions, then we know that the total length of the eyepiece graticule is 0.2 mm
• The graticule is divided by a scale from 0 to 100, which means that each individual division is a length of 0.002 mm
• Take away the stage micrometer and add sample, using the eyepiece graticule to measure its size

Question 3

Eyepiece graticule:

Answer 3

translucent ruler with numbers but no units fitted into the eyepiece of a microscope

Question 4

Stage micrometer:

Answer 4

placed on the stage - it is a microscope slide with an accurate scale (it has units) and is used to work out the divisions on the eyepiece graticule at a particular magnification

Question 5

How do you use a light microscope to examine specimens on a microscope slide?

Answer 5

1. Clip the slide containing the specimen on the stage
2. Select lowest powered objective lens
3. Look down eyepiece lens and use coarse adjustment knob to move stage upwards towards objective lenses until image is roughly in focus
4. Adjust fine adjustment knob until clear image of specimen on slide formed
5. Switch to higher objective lens to increase magnifiation of image