Ch. 2.1 : Microscopy Flashcards
How was cell theory developed?
Light microscopes were invented. Eventually these were developed enough that scientists had access to microscopes with a high enough level of magnification to allow them to see individual shapes.
What is cell theory?
It states :
- both plant and animal tissue is composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
What are the advantages of light microscopy ?
- easily available
- relatively cheap
- can be used out in the field
- can observe both dead, prepared specimens and living organisms
How does a light microscope work?
A compound light microscope has two lenses : the objective lens which is near the specimen and an eyepiece lens through which the specimen is viewed.
The objective lens produces a magnified image, which is magnified again by the eyepiece lens. This objective / eyepiece lens configuration allows for much higher magnification and reduced chromatic aberration than that in a simple light microscope.
Illumination is usually provided by a light underneath the sample. Opaque specimens can be illuminated from above with some microscopes.
What are the different types of sample preparation?
Dry mount - solid specimens are viewed whole or cut into thin slices ( sectioning )
Wet mount - specimens suspended in a liquid eg water or immersion oil. Good for viewing aquatic samples.
Squash slides - wet mount prepared, then lens tissue used to gently press down the cover slip. Damage to cover slip avoided by squashing sample between two slides. Good for viewing things like root tips.
Smear slides - edge of slide used to smear sample creating a thin , even coating on another sample. Good for viewing things like cells in blood.
Why is staining used?
In normal light microscopes there is low contrast between the structures. Stains increase contrast as different components take up stains to different degrees. This allows them to become visible so they can b identified.
