2.1.2 Slides and photomicrographs

Optical microscopes are used to view a wide range of specimens
1. Living organisms like paramecium and amoeba
2. Smear preparations of human blood and cheek cells
3. Thin sections of animal, plant or fungal tissue e.g. bone, muscle, leaf, root or fungal hyphae
Observing unstained specimens
1. Many biological structures are colourless and transparent
2. Some microscopes use light interference rather than light absorption = produces a clear image without staining
3. Some microscopes use a dark backdrop against the illuminated specimen
4. Useful for studying living specimens
Staining specimens
1. Stains= coloured chemicals that bind to molecules on/in the specimen making it easy to see
2. Methylene blue = all purpose stain
3. Differential staining= some stains bind to specific structures staining them each differently to be identified
4. Acetic orcein = binds to DNA, stains chromosomes dark red
5. Eosin = stains cytoplasm
6. Sudan red= stains lipids
7. Iodine (in potassium iodide solution)= stains cellulose in plant walls yellow and starch granules blue/black
Observing prepared specimens
1. Permanently fixed slide are made by experts in labs by:
  1. Dehydrating specimens
    1. Embedded in wax to prevent distortion when slicing
      1. Special instrument makes v. thin slices (sections) which are stained and mounted in a special chemical to preserve them
Calculations involving magnification
1. If you know the magnification on a photomicrograph, you can work out the actual size of the strucutres
  1. Measure the widest part in mm
    1. Convert to um by X1000
      1. Divide this by magnification (tells you actual size)
2. If you are told actual size of a structure on a photomicrograph and you measure the image size in um, you can calculate magnification factor
  1. M: I/A
    1. M= magnification factor
      1. I= Image size, um
        A= actual size
      2. If magnification factor is 1000 it must be written as X1000

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2.1.2 Slides and photomicrographs

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