Summary
Summary Light and Electron microscopes
- Module
- Unit 2 - Cells
- Institution
- AQA
Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
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Light and electron microscope summary notes15 September 2022 10:03
Magnification- the factor by which the image is enlarged compared to the original object
Resolution- the ability of a microscope to distinguish between structures that are very close
Light microscopes
- Glass lenses used
- Light passed through at 400-700 nm of wavelength - too long so reduces resolution - le
- Parts of specimen absorb different amounts of light and different wavelengths
- Light not absorbed is transmitted to the eye through the objective lens and eyepiece
- Resolution- 200 nm
- Magnification- x1500
- Cheap costs
- Specimen can be alive or dead
Electron microscopes
- Electromagnetic lens
- Resolution- 0.2nm
- Magnification- x250000
- Specimen must be dead
- More expensive
- TEM (transmission electron microscope)- beams of electrons are passed through the s
sample - some are absorbed by the cell which creates darkness on the image, others p
screen so these parts of the image appear bright
- Micrograph is produced- 2D
- Chemicals are required for specimen- creates artefacts - structures not originally prese
specimen
- Higher resolution than scanning EM
- SEM (scanning electron microscopes) - electrons bounce off the surface of the specime
the reflected electrons
- Specimen is much thicker as do not need to penetrate through
- 3D image is produced
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