Magnification and Resolution
Magnification - how much bigger the image is than the specimen (the sample your looking at)
Formula for magnification = length of image/length of specimen
ie. if you magnified image that's 5mm wide and your specimen is 0.05mm wide the magnification is: 5/0.05= times 100
Resolution - how detailed the image is. More specifically, it's how well a microscope distinguishes between two points that are close together. If a microscope lens can't seperate two objects, then increasing the magnificationwon't help.
Light and Electron Microscopes
- They use light.
- They have lower resolution than electron microscopes.
- They have a maximum resolution of about 0.2 micrometres (um).
- The maximum useful magnification of a light microscope is about times 1500.
- They use electrons instead of light to form an image.
- They have a higher resolution than light microscopes so give a more detailed image.
- They have a maximum resolution of about 0.0001 micrometres (about 2000 times higher than light microscopes.)
- The maximum useful magnification of an electron microscope is about 1,500,00.
Electron microscope; TEMs and SEMs
Transmitting Electron Microscopes (TEMs);
- TEMs use elctromagnets to focus a beam of electrons, which is then transmitted through the specimen.
- Denser partsof the specimen absorb more electrons, which make them look darker on the image you end up with.
- TEMs are good because they give high resolution images.
- But they can only be used on thin specimens.
Scanning Electron Microscopes (SEMs);
- SEMs scan a beam of electrons across the specimen.
- This knocks of electrons from the specimen, which are gathered in a cathode ray tube to form an image.
- The images you end up with show the surface of the specimen and they can be 3D.
- But they give lower resolution images than TEMs.
Cell Fractionation Seperates Organelles
2) Filtration- gettng rid of the big bits. The solution is filtered though a gauze to seperate any large cell debris or tissue debris. The organelles are much smaller than the debris, so they pass through.
3) Ultracentrifugation - Seperating the organelles.
- The cell fragments are poured into a tube. This tube is put into a cetrifuge and spun at a low speed. the heaviest organelles, like nuclei, get flung to the bottom - the pellet. The rest of the organelles stay suspended in the fluid above the sediment - the supernatant.
- The supernatant is drained off, poured into another tube, and spun in a centrifuge at a higher speed.