Microscopy

• Magnification is how many times larger an image is than the object
• Resolution is the ability to distinguish between two separate points or how detailed the image is
• magnification = image size ÷ object size
• An eyepiece graticule is a small scale placed within the eyepiece
• A stage micrometer is used to calibrate the eyepiece graticule which is a glass slide with a scale measured in µm
• The graticule is calibrated:

  1. Fix the stage micrometer into place on the stage
  2. Look through the eyepiece to line up the micrometer and the graticule
  3. Count the number of graticule divisions that fit into one micrometer division
  4. Use the formula to calculate the size of each graticule division at the magnification
  5. graticule division = size of one micrometer division ÷ number of graticule divisions
• Light microscopes work by creating an image that is much larger than the real object
• Light microscopes have a lower resolution and magnification compared to other microscopes
• Preparing a wet mount:

  1. Pipette a small drop of water onto the glass slide
  2. Use forceps to place a thin section of specimen onto water, thin enough to allow light through
  3. Add drops of stain to specimen increasing contrast allowing cell components to be visible
  4. Add cover slip over specimen
• Differential staining is using more than one chemical stain to distinguish between cells or organelles
• Dry mounting is placing the specimen directly onto the slide and covered with cover slip
• Squash slides is a wet mount but the cover slip is pressed to squash the cells
• Smear slides use the edge of a slide to smear the sample to create a thin even coating on a slide
• Transmission and scanning electron microscopes have a higher magnification than light microscopes
• Scanning electron microscopes have the highest resolution
• Light microscopes are much cheaper than transmission and scanning electron microscopes
• The sample preparation for a light microscope is much simpler than transmission and scanning electron microscope
• The image produced on a light microscope is 2D and in colour
• The image produced on a transmission electron microscope is 2D and black and white
• The image produced on a scanning electron microscope is 3D and black and white
• The specimens used in light microscopes can be living or dead
• Electron microscopes can only observe dead specimens