Using the Metric System to Express the Sizes of
Microbes
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Metric units are used to express the sizes
of microbes
The basic unit of length in the metric
system is the meter (m); it is equivalent to
39.4 inches
The sizes of bacteria and protozoa are
usually expressed in terms of micrometers
(μm). A micrometer is one millionth of a
meter
A typical spherical bacterium (coccus) is
approximately 1 μm in diameter
A typical rod-shaped bacterium (bacillus)
is approximately 1 μm wide x 3 μm long
The sizes of viruses are expressed in terms
of nanometers (nm). A nanometer is equal
to one billionth of a meter
Most of the viruses that causes human
diseases range in size from 10 to 300 nm
One exception is Ebola virus, a cause of
viral hemorrhagic fever. Ebola viruses can
be as long as 1,000 nm (1 μm)
When using a microscope, the sizes of
microorganisms are measures using an
ocular micrometer
o This must be calibrated using a
stage micrometer for each
microscope objective
o Stage micrometer acts as a scale of
measurement
Early Microscopes
Representations of Metric Units of Measure and
Numbers
MICROSCOPY
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Observation by the Means of the
microscope
Visualization of structure that is beyond
the resolving power of the eyes
Used of Microscope:
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Relative Sizes of Staphylococcus and Chlamydia
Bacteria and Several Viruses
Qualitative purposes-if present or absent
Morphologic identification-of structures
Localization of tissue reactionimmunologic chemistry
Magnification-enlarge an object
Resolution-discriminate between 2
different minute points; provide resolving
power