Electron Microscopes (OCR Gateway GCSE Biology: Combined Science)

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Increased Resolution

  • Light microscopes use light and lenses to form a magnified image (make the specimen look larger)
  • With a light microscope it is possible to see images of cells and large sub-cellular structures (like nuclei and chloroplasts), although stains are often required to highlight certain parts of cells
  • Light microscopes have limited magnification and resolution (how well two points that are close together can be distinguished)
    • Electron microscopes helped address these limitations
  • The first electron microscopes were developed in the 1930s.
    • Electron microscopes use beams of electrons, rather than light, to visualise specimens
    • The wavelength of an electron beam is much smaller than that of visible light, which gives electron microscopes a much higher resolution and magnification
    • Electron microscopes allow smaller structures can be viewed in more detail
    • This has improved our understanding of sub-cellular structures such as the internal structure of mitochondria

Transmission Electron Microscopy

  • Transmission Electron Microscopes (TEMs) are the most powerful type of electron microscopes
  • They have a higher magnification and resolution than other microscopes with a maximum magnification of approximately 50 000 000 X (50 million times)
    • This has helped biologists develop a better understanding of the structure of the nucleus and cell membrane
  • You will not find an electron microscope in school. They are very expensive, not portable and it is a complicated process to prepare samples

Comparing Light Microscopes & Electron Microscopes

Images from a light microscope

  • The image below represents an image of a cross-section of a leaf taken with a light microscope
  • The sample can be stained to help visualise distinct structures 
  • The overall structure of the leaf can seen and different types of individual cells identified
    • Nuclei (pink dots) in some cells can be observed
    • under a higher magnification, chloroplasts would be seen

Leaf Photomicrograph

Light microscope photomicrograph of the cross-section of a leaf

Images from an electron microscope

  • The image below represents a Transmission Electron Micrograph of a palisade mesophyll cell
  • A much higher magnification can be attained with the TEM
  • Sub-structures like the cell wall, chloroplasts and nucleus can be observed in more detail
    • Distinct layers can be seen inside the chloroplasts
    • Granular material can be seen in the nucleus - this is DNA 
  • Electron micrographs are black and white although false colour can be added afterwards 

Electron micrograph and drawing of a palisade mesophyll cell

Electron micrograph and a drawing of a palisade mesophyll cell

Table to compare electron microscopes and light microscopes

Comparison of the Electron Microscope and Light Microscope table

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Author: Phil

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.