Exam preparation Biology

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  • Created by: 15howardl
  • Created on: 16-09-21 17:48

MICROSCOPY:

The cell theory states that both plant and animal tissue is composed of cells; cells are the basic units of all life and cells only develop from existing cells

Light microscopes were the first type of microscopes to be developed (16th - 17th century). Sicne then many other microscopes have been developed and improved however the light microscope still gets used today. First of all they are easily available, they are also relatively cheap and can be used out in the field.

Light microscopes can be used to observe living organisms as well as dead, prepared specimens.

A compound light microscope has two lenses - the objective lens which is placed near the speciment and then the eyepiece lens which is what you look through. The objective lens produces a magnified image which is then magnified again by the eyepiece lens. By having both the objective and eyepiece configuration it allows for much higher magnification and reduce chromatic aberration (colour fringing). Illumination is usually provided by a light underneath the sample, if the speciment is opague you can just illuminate the specimen from above.

Sample preparation:

Dry mount - Solids specimens are viewd whole or cut into very thin slices with a sharp blade (sectioning). The specimen is then place on the centre of the slide and a cover slip is placed over the sample. This could be hair, pollen and insect parts which can get viewed whole. Then you have muscle tissue or plants that get sectioned to get viewed this way

Wet mount - Specimens are suspended in a liquid such as water or an immersion oil. A cover slip is placed on from an angle, For example, aquatice samples and other living organisms can be viewed this way

Squash slides…

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