Biology - unit 2 - cells

  • Created by: Silk16
  • Created on: 09-05-22 09:53
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  • Methods of studying cells
    • Light Microscopes
      • Magnification = size of image/size of real object
      • Wavelength of light restricts the resolution
      • Resolution is defined as the minimum distance apart that two objects can be distinguished as separate objects in an image. The greater the resolution the more clear the image will be.
    • Electron Microscopes
      • Transmission electron microscopes (TEM)
        • A beam of electrons passes through a thin section of a specimen. Areas that absorb the electrons appear darker on the electron micrograph that is produced.
      • Scanning electron microscopes (SEM).
        • In a scanning electron microscope a beam of electrons passes across the surface and scatter. The pattern of scattering builds up a 3D image depending on the contours of the specimen.
      • Limitations
        • The whole system must be in a vacuum so living specimens cannot be observed.
        • Specimens have to be very thin, particularly for TEM so that the electrons can pass through.
        • SEM has a lower resolving power than TEM, but both have greater resolving power than a light microscope.
    • Cell fractionation
      • The process in which different parts and organelles of a cell a separated so that they can be studied in detail
        • Differential centrifugation.
      • Homogenation
        • .The cells are first blended in an homogeniser forming the resultant fluid called the homogenate. This tube of homogenate is then placed in a centrifuge and spun at a slow speed.
          • The heaviest organelles, the nuclei, are forced to the bottom of the tube where a thin sediment or pellet forms.
            • The fluid at the top, called the supernatant, is removed which leaves just the sediment of the nuclei. The supernatant is then transferred to another tube and spun at a slightly faster speed. This time the pellet that forms contains the next heaviest organelle, the mitochondria.
              • Repeated with the speed increased


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