B1.1

• Flow chart on microscope

  Light Source -> Stage -> Slide -> Object -> Objective lens -> Body tube -> Eyepiece lens ->eye
• What is a microscope?


  An instrument used to magnify small objects to make them larger.
• Define Magnification


  How many times larger the image is than the object
• Whats resolution?


  Ability to distinguish to points.

  It is the resolving power that controls how detailed the image is.
• When was the light microscope made?

  Mid 17th century
• When was the electron microscope made?

  1930's
• Advantages of light microscopes

  • Cheap
  • Easy to use
  • Portable ( can be used anywhere )
  • Can use live specimens
  • Coloured images
• Advantages of electron microscopes

  • High magnification ( x 2,000,000)
  • High resolving power ( Transmission electron microscope - 0.2 nm / Scanning electron microscope - 10 nm )
  • Sub-cellular structures are more visible
• Disadvantages of light microscopes

  • Low magnifications ( x 2,000 )
  • Low resolution (200 nm )
• Disadvantages of electron microscopes

  • Large and expensive
  • Only able to view dead species
  • Black and white images
  • Has to be maintained in special conditions ( Eg. pressure, temp )
• Unit conversions

  1km - 1000m

  1m - 1000mm

  1mm - 1000Um (micrometer)

  1Um - 1000nm
• Formulae for image, magnification and object/actual size


  Image = A X M

  Magnification = I / A

  Actual/ object size = I / M
• How else can you calculate magnification?

  Eyepiece lens magnification X Objective lens magnification
• Define the base of a microscope

  lowermost part of the microscope

  supports the entire microscope structure.
• Define the eyepiece of a microscope

  Located at the top of the microscope.

  This part is used to look at the specimen. 

  It has a set magnification
• Objective lenses


  The objective lens is the lens that is closest to the specimen.

  Fitted on the nosepiece.

  A standard microscope has 3 to 4 objective lenses of different magnifying powers
• Adjustment Knobs are the control knobs used to focus the microscope on the specimen.
• Fine adjustment knob


  It is a smaller knob and is used to move the stage up or down very slowly.

  It is used to sharpen the image.

  It is mostly used while viewing under high power.
• Coarse adjustment knob


  Coarse Adjustment Knob is used for focusing the image under low power magnification.

  It is a larger knob and is used to move the stage up or down very rapidly.
• Stage


  This is the section in which the specimen is placed for viewing. They have stage clips that hold the specimen slides in place. 
• Transmission electron microscopes give a 2d image with a high magnification and resolution.
• Scanning electron microscopes provide 3d images however with a lower magnification.
• Transmission electron microscopes (TEMs) are used to examine thin slices or sections of cells or tissues. Scanning electron microscopes (SEMs) have a much larger field of view so are used to look at the surface of larger specimens at lower magnifications.