Lab%201:%20Using%20the%20Microscope

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Lab 1 Using the Microscope

• Biology 2201, Unit 1

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Safety in the Lab

• Read and heed the Laboratory Safety guidelines on
  pages x to xi in the McGraw-Hill Ryerson Biology
  text.
• Read the 1st Lab on pages 15 to 19 and page 24 in
  the text.
• Familiarize yourself with the locations of the
  safety equipment in the Science Lab.

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Magnification

• To calculate the total magnification of an
  object, multiply the power of the eyepiece by the
  power of the objective.
• For example, if the eyepiece magnification is 10x
  and the low-power objective is 4x, the total
  magnification of the low-power objective is 10 x
  4 40x.

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Illumination

• The light source (electric bulb) directs light
  through the diaphragm, the specimen and the lens.
• Look through the eyepiece, and adjust the
  diaphragm until the view is as bright as
  possible.

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Field of view

• The area that you can see through the eyepiece is
  called the field of view.
• To determine the field of view, place a clear
  plastic ruler on the stage.
• With the low-power objective in place, use the
  coarse adjustment knob to focus on the ruler.
  Position the ruler so that one of the millimetre
  markings is at the left edge of the field of
  view.

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Calculate the size of your F.O.V.
The diameter of the field of view under
low-power, shown here, is about 1.5 mm.
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• If you know the diameter of the field of view for
  the low-power lens, you can calculate the field
  of view for the medium-power lens as follows
  (example only)
• Med-power FOV
• Low-power FOV x Magnification of low-power
  objective
• Magnification of med-power objective
• 2 mm x 4X
• 10X
• 2 mm x 0.4
• 0.8 mm or 800 µm is the Med-power FOV

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Formula for calculating thehigh-power FOV

• High-power FOV
• Low-power FOV x Magnification of low-power
  objective
• Magnification of high-power objective

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Measurement

• Objects in the field of view of a microscope are
  usually measured in micrometres (µm).
• For example
• 1 µm equals 0.001 mm
• 1000 µm equals 1 mm
• From our example, the FOV under the medium-power
  objective is 0.8 mm x 1000 800 µm.

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Calculating specimen size

• You can determine the size of a specimen, such as
  a microscopic amoeba, by estimating how many
  could fit end to end across the field of view.
• To do this, divide the field of view by the
  number of specimens.

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For example, if the field of view in the
illustration is 1500 µm, what is the diameter of
each amoeba?
Answer Specimen size FOV divided by of
specimen 1500 µm divided by 5 300 µm is
the diameter of an amoeba.
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Focusing techniques

• The low-power objective should be in position.
• Center the specimen over the opening in the
  stage.
• Look through the eyepiece. Slowly turn the coarse
  adjustment knob until the object is in focus.
• Use the fine adjustment knob to sharpen the
  focus.
• Carefully rotate the revolving nosepiece to the
  medium-power objective.
• Watch the side of the stage as you rotate the
  nosepiece to make sure that the objective lens
  does not strike the surface of the slide.
• Adjust the focus using only the fine adjustment
  knob.
• To finish, carefully rotate the nosepiece until
  the low-power objective is in place remove
  slide power off.

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Biological drawings

• Biological drawings are drawings of biological
  specimens that you observe under the microscope.
• A scale drawing is a drawing in which the
  proportions of what you observe through a
  microscope are kept constant.

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• Label your drawing.
• Indicate the total magnification.
• Calculate the actual size of the specimen.

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Depth of field

• The depth of field is the vertical distance (the
  thickness of an object) that remains in focus
  at any one time while the specimen is being
  viewed.

Video link
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Preparing a wet mount

• Start with a clean slide and coverslip.
• Hold the slide and coverslip by their edges to
  avoid getting your fingerprints on their
  surfaces.
• Using tweezers, position the specimen in the
  centre of the slide.
• With the medicine dropper, place one drop of
  water on the specimen.

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• Hold a coverslip over the sample at a 45 angle.
  One edge of the coverslip should touch the
  surface of the slide near the specimen.
• Lower the opposite edge of the coverslip over the
  sample. Make sure that no bubbles form beneath
  the coverslip.

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Next day we meet in the Lab.

• Be prepared!