OCR AS 1.1.1 - Microscopy

OCR AS 1.1.1 - Microscopy

1. Magnification - the degree to which the size of an image is larger than the object iteself

2. Resolution - the degree to which it is possible to distinguish between two objects in close proximity

3. The Light Microscope has a magnification of x1500 and a resolution of 200nm

   • Staining is used to help visualise cells and their components by providing contrast. Different chemicals will take up different amounts of the stain so will appear different colours.
   • the sample may also be embedded in wax so thin sections can be cut without distorting the specimen

4. Transmission Electron Microscopes have a magnification of x500,000 and a resolution of 0.1nm

   • the electron beam passes through the sample; denser areas are harder to pass through, so this provides contrast and creates a 2D image
   • Using electron microscopes means the sample must be cut into very thin pieces using a diamond knife, embedding in resin, removing the water from the sample and replacing with ethanol and freezing it.

5. Scanning Electron Microscopes have a magnification of 100,000 and a resolution of 0.1nm.

   • the electron beam bounces of the sample and produces a 3D image
   • the sample must be placed in a vacuum because electrons will bounce of airbourne particles
   • lead salts may be used for staining in order to scatter electrons differently and gives contrast

6. Magnification = Image Size / Actual Size

7. 1mm = 1000um