Studying Cells - How Microscopes Work

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  • Studying Cells - How Microscopes Work
    • Magnification is Size, Resolution is Detail
      • Magnification is how much bigger the image is than the specimen (the sample you're looking at).
        • It's calculated using this formula: magnification = image size / object size.
      • Resolution is 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 separate two objects, then increasing the magnification won't help.
    • You Need to be Able to Calculate the Magnification of an Image
      • In the exam, you might be told the actual and magnified size of an object and then be asked to calculate the magnification. You can do this using the formula.
        • You might also have to rearrange the formula to work out the image size or object size.
    • You Need to Know About Three Types of Microscope
      • Light microscopes
        • Light microscopes use light.
        • They have a lower resolution than electron microscopes - they have a maximum resolution of about 0.2 micrometres.
          • So they're usually used to look at whole cells or tissues.
        • The maximum useful magnification of a light x 1500 microscope is about
      • Laser Scanning Confocal Microscopes (a special type of light microscope)
        • Laser Scanning Confocal Microscopes use laser beams (intense beams of light) to scan a specimen which is usually tagged with fluorescent dye.
        • The laser causes the dye to fluoresce - give off light.
          • The light is then focused through a pinhole onto a detector.
            • The detector is hooked up to a computer, which generates an image
              • The image can be 3D.
        • The pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.
        • They can be used to look at objects at different depths in thick specimens
      • Electron Microscopes
        • Electron microscopes use electrons instead of light to form an image. They have a higher resolution than light microscopes so give more detailed images. There are two kinds of electron microscope:
          • Transmission electron microscope (TEM) - use electromagnet-s to focus a beam of electrons, which is then transmitted through the specimen
            • Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
              • TEMs are good because they provide higher resolution images (so they can be used to look at a range of organelles) but they can only be used on thin specimens.
          • Scanning electron microscopes (SEM) - scan a beam of electrons across the specimen.
            • This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
              • The images produced show the surface of the specimen and can be 3D.
                • But they give lower resolution images than TEMs.
    • You Need to be able to compare Magnification and Resolution
      • You need to know about the magnification and resolution of light microscopes and both types of electron microscopes.


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