The Microscope

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The Microscope
The Cell
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Human beings have very limited vision
We cannot see things that are very small
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Or very far away
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As scientists, we want to investigate these
worlds that are normally invisible to us
To do this, we must employ technology in the form
of telescopes and microscopes
We use these instruments as extensions of our
normal vision
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The unaided human eye can detect objects as small
as 0.1 mm in diameter
Most cells are far smallerbeyond the limits of
our visual acuity
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The light microscope can extend our vision a
thousand times
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Most cells are between 1 and 100 µm in
diameter These cells will be visible to us only
under a microscope
Here
To Here
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Today we will learn to use the compound microscope
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Microscopy involves three basic concepts

• Magnification The degree to which the image of
  a specimen is enlarged

• Resolving Power How well specimen detail is
  preserved

• Contrast The ability to see specimen detail
  against its background

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Important Points to Remember!

• Be very careful when handling and carrying the
  microscopes

• Our microscopes have an oil objective lens for
  high-power viewing Do Not get oil on the other
  objective lensesthey will be ruined!

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Calculating Total Magnification
The eyepiece lenses are 10-power (10X)
To get the total magnification, we multiply the
power of the eyepiece (10X) by the power of the
objective lens we are using
Eyepiece Objective Total Magnification
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Our scanning objective is 40X Calculate the
total magnification when using this objective
10X 40X 400X
When using the scanning objective, total
magnification is 400X All other magnifications
can be calculated this way
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Measuring the Diameter of the Field of View
1 mm
About 0.2 mm
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So
This is our approximate field of view when using
the scanning objective
We can use this information to get a rough
estimate of the size of the objects we are viewing
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If this is our object, and our field of view is
about 4200µm, this object is between 900 and
1000µm
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The Cell
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Cell Theory
Currently, cell theory consists of three
postulates

• All organisms are composed of one or more cells
• Cells are the fundamental units of life
• All cells arise from preexisting cells

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The two basic types of cells are

• Prokaryotic cells that have no membrane-enclosed
  nucleus

• Eukaryotic cells which do have a
  membrane-enclosed nucleus

Prokaryotic cells are found in the domains
Bacteria and Archaea
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Remember The main difference between prokaryotic
and eukaryotic cells is that eukaryotic cells
have a membrane-enclosed nucleus, and prokaryotic
cells do not
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A prokaryotic cell
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Overview of an animal cell
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Overview of a plant cell
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Have you ever wondered why cells are so small?
It is a geometric problem Because cells depend
on exchange of materials with their environments,
a high ratio of surface-area-to-volume is needed
for maximum effect
As an object increases in size, its volume grows
proportionately more than its surface areathe
smallest cells have the highest ratio of
surface-area-to-volume
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Cells are represented as boxes in the diagram