Light microscopes Flashcards
1
Q
How it works:
A
- Has 2 lenses - objective lens placed near the specimen, and an eyepiece lens through which the specimen is viewed
- Objective lens produces magnified image (x4, x10, x40) which is magnified again by eyepiece (x10)
- This configuration allows for higher magnification and reduced chromatic aberration
- Illumination provided by a light or mirror under the sample
2
Q
Sample preparation:
A
- Dry mount: Solid specimens are viewed whole/cut into very thin slices (sectioning). Specimen is placed on the centre of slide and cover slip in placed on the sample.
- Wet mount: Specimens suspended in liquid. Cover slip is placed on from an angle.
- Squash slides: squashing sample between 2 slides
- Smear slides: Use edge of slide to smear the sample and create a thin coating
3
Q
Use of staining:
A
- Sample is illuminated from below by white light and observed from above (brightfield microscopy). Whole sample is illuminated at once (wide-field microscopy).
- Imaged have low contrast as most cells don’t absorb lot of light. Resolution is limited by wavelength of light.
- Cytosol of cells are often transparent.
- Stains INCREASE CONTRAST as different components within the cell take up stains to different degrees based on charges of dyes as cytosol is negative
- Allows organelles to be identified (Differential staining)
4
Q
Using a graticule:
A
- Eyepiece graticule is a disc marked with a fine scale of 1-100. Has no units.
- Stage micrometre is a slide with very accurate scale in micrometres engraved on it : 100 divisions = 1mm so 1 division = 10um
- Magnification factor = num. of micrometres/ num. of graticule divisons
