Microscopy F211
- Created by: Eleanor Izzard
- Created on: 06-12-12 20:18
View mindmap
- Microscopy
- Magnification - the degree to which the size of an image is larger than the object itself.
- I = A/M
- total magnification of a specimen is given by timesing the objective by the eyepiece magnification
- Resolution - the degree to which it is possible to distinguish between two objects that are very close together.
- Limits - human eye 100, light microscope 200nm, electron microscope 0.2nm
- Micrometre = µm = 0.000001m
- nanometre = nm = 0.000000001
- Light Microscopes
- use a number of lenses to produce an image
- can be viewed directly by eye
- light passes from a bulb under the stage, through a condenser lens, through the specimen. Focused through objective lens, then through eyepiece lens
- Have a number of different lenses to be rotated into position
- 4 objective lenses - x4 x10 x40 x100 (x100 oil immersion lens)
- Specimens produced by staining (chemicals that bind to chemicals on/in the specimin
- Or by Sectioning (specimens put in was, thin sections cut, wax melted)
- can be used to measure organelles (use graticule)
- Value of intervals on graticule: x40 - 25µm, x100 - 10µm, x400 - 2.5µm, x1000 - 1.0µm
- use a number of lenses to produce an image
- Electron Microscopes
- Scanning Electron
- 3D image produced
- electron beam directed onto sample, electrons don't pass through, they bounce off
- maximum magnification x 100,000
- Transmission Electron
- electron beam passes through thin sample
- electrons pass through denser parts of the sample less easily, creating contrast
- 2D image produced
- maximum magnification x 500,000
- Advantages - resolution 0.1nm, more detailed images gained of organelles, SEM produces 3D images revealing contours and tissue arrangements.
- Disadvantages- electron beams deflected by air molecules so must be in a vacuum, expensive, preparing samples requires a high level of training and skilll
- electron micrographs can be put into colour
- preparing a sample: fix specimen in glutaraldehyde to firm tissue, dehydrate it, replace water with ethanoll, embed in solid resin, cut thin (diamond knife) stain (lead salts), mount (copper grid)
- Scanning Electron
- Magnification - the degree to which the size of an image is larger than the object itself.
Similar Biology resources:
Teacher recommended
Comments
Report