2.1 Foundations in bio a-level

• How do transmission electron microscopes work?

  They pass a beam of electrons through a specimen to create an image
• What is the maximum magnification of transmission electron microscopes?

  Up to 2 million times
• What is the difference between scanning electron microscopes and transmission electron microscopes?

  Scanning electron microscopes produce 3D images, while transmission electron microscopes produce 2D images
• What is the resolution of electron microscopes compared to optical microscopes?

  Electron microscopes have much greater resolution
• What is differential staining?


  A technique that stains specific cell structures differently for easy identification
• What is the function of methylene blue in microscopy?


  It is an all-purpose stain
• How do you calculate total magnification?

  Total magnification = magnifying power of the objective lens x magnifying power of the eyepiece lens
• If the magnifying power of the objective lens is 40 and the eyepiece lens is 10, what is the total magnification?


  Total magnification = $40 \times 10 =$$400$
• What should you consider when observing structures in a microscope section?

  Cells have a 3D structure, and the section may not show all structures
• What are the steps to prepare and examine microscope slides?

  1. Place the specimen on the stage and clip it in place.
  2. Adjust the focus knobs to get a clear image.
  3. Use staining if necessary to enhance visibility.
  4. Follow the magnification formula for calculations.
  5. Draw and annotate the observed structures.
• What are the rules for making clear, labelled drawings of specimens under a light microscope?

  • Use a sharp HB pencil.
  • Include a title and magnification used.
  • Indicate the scale of the drawing.
  • Make a low-power plan without individual cells.
  • Label areas clearly and accurately.
• What is the purpose of using a dark background in microscopy?


  To enhance the visibility of illuminated specimens
• What is the significance of using prepared and permanently fixed slides?

  They prevent distortion during slicing and preserve the specimens