Microscopes & Magnification

• What has microscope technology allowed us to see more of?

  The structures of cells and the role of sub-cellular structures
• Why could people not see cells in organisms before microscopes were invented?

  Because microscopes were not available to magnify small structures
• What is the greatest possible magnification of a light microscope?

  About ×2000
• How does an electron microscope differ from a light microscope?

  An electron microscope uses electrons to view objects, allowing for higher magnification
• What is the maximum magnification possible with an electron microscope?

  About ×10 million
• Why can you see objects in cells more clearly with an electron microscope?

  Because it provides far more detail than a light microscope
• What is the formula for calculating magnification?

  magnification (M) = image size (I) / real size (R)
• How do you convert image size from millimetres to micrometres?

  Multiply by 1000
• What should you do if the image has a scale bar?

  Use the scale bar to find the answer
• In the worked example, what is the image size (I) if the scale bar is 20 µm?

  20 µm
• What is the real size (R) in the worked example?

  1 µm
• What is the magnification calculated in the worked example?

  ×20000
• How do you calculate the magnification of cells viewed with a ×4 eyepiece and a ×20 objective?

  Multiply the eyepiece magnification by the objective magnification
• What is the total magnification when using a ×4 eyepiece and a ×20 objective?

  80 times
• If a bacterium is viewed under a light microscope with a ×40 objective and a ×10 eyepiece, what is the image length given?

  1. 2 mm
• How do you find the actual length of the cell from the image length?

  Use the magnification formula to calculate it
• What is the first step in using a light microscope safely?

  Start with the low power objective under the eyepiece
• What should you do to secure the slide on the stage?

  Clip the slide securely
• How should you adjust the light source when using a light microscope?

  Adjust it so that light goes up through the slide
• What is the purpose of the coarse focusing wheel?

  To focus on the slide
• What should you do if you cannot see the part of the slide you need with a higher power objective?

  Go back to using the lower power objective to center and focus
• What is the lens closest to the specimen called?

  Objective
• What are the steps to safely use a light microscope?

  • Start with the low power objective
  • Clip the slide securely on the stage
  • Adjust the light source for optimal visibility
  • Use the coarse focusing wheel to focus
  • Center the cell in view before switching to higher power
  • Use the fine focusing wheel for detailed focus
• How do you calculate the actual length of a cell from its image length under a microscope?

  1. Measure the image size (I) in mm
  2. Convert to micrometres by multiplying by 1000
  3. Use the magnification formula:

  $magnification (M) =$$\frac{I}{R}$

  1. Rearrange to find real size (R):

  $R =$$\frac{I}{M}$

  1. Calculate the actual length
• What is the aim of the core practical described in the study material?

  To produce a labelled diagram of a plant cell.
• What apparatus is needed to produce a labelled diagram of a plant cell?

  • Light microscope
  • Unlined paper
  • Sharp HB pencil
  • Ruler
  • Rubber
• What should you do if a line in your drawing is in the wrong place?

  Rub it out cleanly before drawing it in the correct position.
• How should the relative sizes of structures in the drawing be represented?

  They should be kept approximately correct.
• Where should labels be placed in the drawing?

  Labels should be outside the drawing.
• What must not happen with label lines in the drawing?

  Label lines must not cross.
• What should you use to draw label lines linking labels to the correct parts of the drawing?

  A ruler.
• What should you never use in your drawing?

  Shading.
• What should the title of your drawing indicate?

  What the specimen is and the magnification used.
• How should you calculate the magnification for your drawing?

  Refer to the guidance provided on page 3.
• What should you focus on while making the drawing?

  Keep looking at the specimen and only draw what you see.
• What are the key parts of a plant cell that should be included in the drawing?

  • Chloroplast
  • Cell wall (two layers)
  • Cytoplasm
  • Vacuole (not drawn)
  • Nucleus
• What is the target grade for the drawing exercise described in the study material?

  Grade 3.
• What should you do with the cells in a blood smear seen under a light microscope?

  Draw and label one example of each cell in the smear.
• What magnification was used to observe the blood smear?

  x1000.
• Why is it important to use a light microscope for drawing labelled diagrams?

  It allows for accurate representation of cell structures.