Microscopy and Cells

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Magnification: The degree to which the size of an image is larger than the object itself.

Resolution: The degree to which it is possible to distinguish between two objects that are very close together.

Types of Microscope:

Light Microscope: Uses a light source and a number of lenses to produce a magnified image.

Transmission Electron Microscope (TEM): An electron beam passes through a sample, contrast is produced as it is harder to pass through denser parts of the sample. A 2D image is produced with a maximum possible magnification of x500,000.

Scanning Electron Microscope (SEM): An electron beam is directed at the sample, it bounces off to produce a 3D image with a maximum possible magnification of x100,000. 

Advantages of electron microscopes: Better resolution (we can see organelles in detail), and we can see the cell in detail.

Disadvantages: Samples need to be in vacuum, expensive, requires skill and training.

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Prokaryotes vs Eukaryotes

  • Bacteria
  • Don't have a "true nucleus"
  • Only have one membrane- the cell surface membrane- they contain no membrane-bound organelles.
  • Cell wall made of peptidoglycan
  • Capsule outside cell wall acts as protective layer
  • Contains a single DNA loop, and plasmids (very small loops of DNA)
  • DNA found in nucleoid region, this isn't surrounded by a membrane
  • Only some bacteria are harmful, these are called pathogens.


These are generally more advanced and have a true nucleus, they also contain organelles.

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