Microscopes

• Light microscopes use light, which has a longer wavelength and a lower resolution (than electrons).
• Electron microscopes use electrons, which have a shorter wavelength and therefore a higher resolution (than light).
• Transmission microscopes can distinguish between points 0.1nm apart.
• Electron microscopes use a beam of electrons through a vacuum to prevent any obstacles/deflections (electrons passing through air can break apart molecules).
• Electron microscopes cannot observe living organisms in a vacuum. Samples must be stained, thinly sliced, and dehydrated, so the electrons can be absorbed (complex procedure - results in artefacts).
• Images produced by electron microscopes are always in black and white.
• The image produced by an electron microscope may contain artefacts: things that result from the way the specimen is prepared. They appear on the final photomicrograph so it is difficult to determine whether the thing in the photo really is part of the specimen.
• Transmission microscopes produce 2D photomicrographs.
• Scanning microscopes produce 3D images.
• 𝙎𝘾𝘼𝙉𝙉𝙄𝙉𝙂 𝙀𝙇𝙀𝘾𝙏𝙍𝙊𝙉 𝙈𝙄𝘾𝙍𝙊𝙎𝘾𝙊𝙋𝙀 (𝙎𝙀𝙈):

  • SEM directs an electron beam across a sample.
  • SEM can produce 3D images of a specimen.
  • SEM can be used on thick specimens.
  • Limitation: SEM has a lower resolution.
• 𝙏𝙍𝘼𝙉𝙎𝙈𝙄𝙎𝙎𝙄𝙊𝙉 𝙀𝙇𝙀𝘾𝙏𝙍𝙊𝙉 𝙈𝙄𝘾𝙍𝙊𝙎𝘾𝙊𝙋𝙀 (𝙏𝙀𝙈):

  • TEM projects an electron beam through a sample.
  • Denser tissue appears darker in the micrograph.
  • A TEM produces very high-resolution images.
  • Limitation: TEM must be performed in a vacuum.
  • Limitation: TEM can only be used for thin tissues.
• 𝙇𝙄𝙂𝙃𝙏 𝙑𝙎 𝙀𝙇𝙀𝘾𝙏𝙍𝙊𝙉:

  • LMs can be used to visualise living specimens whereas EMs can only work with dead specimens.
  • Light microscopy is relatively quick whereas electron microscopy is time-consuming and complex, (e.g. specimen preparation).
  • Light microscopy is less expensive as a decent electron microscope can cost upwards of a million pounds and the reagents needed to prepare specimens for electron microscopy are much more expensive.
• 𝙀𝙇𝙀𝘾𝙏𝙍𝙊𝙉 𝙈𝙄𝘾𝙍𝙊𝙎𝘾𝙊𝙋𝙀𝙎:

  • Use electrons to form images because electrons are smaller than photons of light: EMs have a much greater resolution than optical microscopes.
  • The maximum resolution of an electron microscope is 0.002 micrometres: EMs can be used to produce very detailed images (electron micrographs) of tiny structures.
  • The maximum magnification is 500,000x because the resolution is so good.
  • Electron micrographs are typically black and white.
  • There are two major types of electron microscopy: TEM and SEM.
• What is an Electron Microscope?

  A type of microscope that uses a beam of electrons to produce high-resolution images of biological samples. Unlike light microscopes, which use light to form images, electron microscopes use a beam of electrons to produce images that are much more detailed and have a much higher magnification.
• How does an Electron Microscope work?

  By firing a beam of electrons at a biological sample, which then interacts with the sample and produces an image. The electrons are focused into a beam using magnetic lenses and are then directed towards the sample. The electrons penetrate the sample and interact with the atoms within it, producing an image that can be captured and viewed on a screen.
• What types of Electron Microscopes are there?

  Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM).

  TEMs produce images by passing electrons through a thin section of a biological sample, while SEMs produce images by scanning the surface of a biological sample with a beam of electrons.
• How does the use of Electron Microscopes contribute to scientific research?

  Provides a much more detailed understanding of cell structure and function. EMs have allowed scientists to study the structures within cells in much greater detail, leading to a better understanding of cellular processes such as protein synthesis, cellular respiration, and cell division. The use of Electron Microscopes has also helped to advance our understanding of diseases and medical conditions.
• What are some limitations of Electron Microscopes?

  • High cost and specialised training required
  • Complex to operate
  • Artefacts/can damage samples
  • Time-consuming and complex preparation of samples
• What are the benefits of using an Electron Microscope?

  • Can observe internal structures within cells, e.g. organelles
  • Can produce three-dimensional images of biological samples
  • High resolution (much more detailed images produced)
  • Have a much higher magnification than light microscopes, allowing for the observation of incredibly small structures within cells.
• Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

  1. TEM use electrons and optical use light;
  2. TEM allows a greater resolution;
  3. (So with TEM) greater detail in organelles can be observed;
  4. TEM view only dead specimens and optical can view live specimens;
  5. TEM does not show colour and optical can;
  6. TEM requires thinner specimens;
  7. TEM requires more complex preparation;