BIOLOGY IN FOCUS
PATTERNS IN NATURE
Chapter 1 Cells and the cell theory
STUDENT ACTIVITY
Table CD1.3 Comparing an electron microscope with a compound light microscope
Feature
(and similarity)
Compound light microscope
Transmission electron
microscope (TEM)
Energy source
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Specimen preparation
Magnification
Resolution
Can live specimens be viewed?
Image: colour/black and white
Advantages
Disadvantages
1
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
Answers
Table CD1.3 Comparing an electron microscope with a compound light microscope
Feature (and similarity)
Compound light microscope
Transmission electron microscope
(TEM)
Energy source
(both have an energy source to allow
specimens to be viewed)
■
Beam of light (from an electric
source or reflected by a mirror)
■
Beam of electrons
Focus
(both focus the image)
■
Light is focused by glass lenses;
image viewed through eyepiece(s)
■
Electrons that bounce off the
specimen are focused by magnets;
image produced on a screen
Specimen preparation
(both involve producing a thin specimen
and creating contrast; both may involve
fixation, embedding, sectioning and
staining)
■
May be simple—a wet mount: slice
with a razor blade, place in a drop
of water and stain
May be more complex—embedded
in wax; sectioned with a microtome,
stained with coloured substances
■
Complex preparation: fixed to kill
specimen, embedded in resin,
sectioned with an ultra-microtome,
stained with heavy metals
Magnification
(both result in the production of
a magnified image)
■
■
Usually up to 1000 ×
Maximum 2000 × in extremely high
quality modern LMs
■
Up to 1 000 000 × (1 million times)
Resolution
(both allow us to distinguish separate
points, parts that appear as a single line
to the naked eye)
■
800 times better than the naked
eye, but much less than an EM
■
100 times better than that of a light
microscope
■
Additional information:
—human eye, resolution up to
0.2 mm
—light microscope, objects closer
than 0.45 µm are no longer seen
as separate objects under a light
microscope
■
Additional information:
—resolution usually up to 0.2 nm
—in theory, EM should have a
resolution up to 0.002 nm,
but technology is still striving
to achieve this
Can live specimens be viewed?
(As a result of fixation, in both some live
specimens cannot be viewed)
■
Yes, in some preparations
(e.g. wet mount)
■
No, because the specimen must be
viewed in a vacuum (TEM)
Image: colour/black and white
■
May be viewed in colour if the
specimen is naturally coloured or
if stains are added
■
Image shows up as fluorescence on
a screen or it may be projected onto
a photographic plate or a computer
screen (black and white)
Colour may be seen with a SEM
■
■
Advantages
■
■
■
Disadvantages
■
■
Affordable, available to schools,
students and general public
Both living and prepared specimens
may be viewed at magnifications
greater than can be seen with the
naked eye
Simple to use; specimen preparation
techniques do not require highly
specialised equipment
■
■
Lower magnification and resolution
Cannot view small detail such as the
structure of organelles
■
■
■
■
High magnification and resolution
Can view structures too small to be
seen with LM
Can view much greater detail,
leading to increased knowledge and
understanding
Live specimens cannot be viewed
More complex fixation and staining,
so may have artefacts compared
with living material
Extremely expensive and not available
to schools and the general public
2
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.