Microbiology
Introduction
What
is
Microbiology?
Microbiology
is
the
study
of
microorganisms,
that
is
the
organisms
which
are
of
microscopic
dimensions.
These
organisms
are
too
small
to
be
clearly
perceived
by
the
unaided
human
eye.
If
an
object
has
a
diameter
of
less
than
0.1
mm,
the
eye
can
not
perceive
(or
more
correctly
resolve)
it
at
all,
and
very
little
detail
can
be
perceived
in
an
object
with
a
diameter
of
I
mm.
Roughly
speaking
organisms
with
a
diameter
of
1
mm
or
less
are
microorganisms
and
fall
into
the
broad
domain
of
microbiology.
Since
most
microorganisms
are
only
a
few
thousandths
of
a
millimeter
in
size.
they
can
only
be
seen
with
the
aid
of
microscope.
As
a
direct
consequence
of
the
invisibility
of
micros
to
the
naked
eye
and
the
need
for
special
techniques
to
study
them,
microbiology
was
the
last
of
the
three
major
divisions
in
biology
(the
other
two
are
botany
and
zoology
to
develop.
Microbiology
is
the
study
of
organisms
that
are
too
small
to
be
clearly
seen
by
the
unaided
eye.
Roughly
speaking,
organisms
with
a
diameter
of
1
mm
or
less
which
can
not
be
seen
by
the
human
eye
unaided,
are
calIed
microorganisms.
These
include
protozoa,
algae,
fungi
and
bacteria
Viruses
are
ultramicroscopic
and
have
an
obligate
parasitic
relationship,
but
for
practical
purposes
these
still
come
under
the
domain
of
microbiology.
At
present,
there
is
general
agreement
to
include
five
major
groups
as
microorganisms:
the
subdivisions
of
virology,
bacteriology,
mycology,
phycology
and
protozoology
(the
studies
of
viruses,
bacteria,
fungi,
algae
and
protozoa
respectively).
Traditionally,
all
organisms
had
been
included
under
the
disciplines
of
either
botany
or
zoology.
Bacteria,
algae
and
fungi
have
in
the
past
been
considered
to
be
the
part
of
the
Plant
Kingdom
while
protozoa
have
been
included
in
the
Animal
Kingdom.
This
view
cannot
be
supported
from
a
taxonomic
standpoint.
Since
microbiology
encompasses
the
study
of
groups
of
organisms
in
all
three
of
these
divisions
of
biology
it
may
be
argued
that
it
covers
a
greater
biological
diver
itv
than
the
other
two
divisions.
Although
microorganisms
have
existed
for
a
long
time,
their
existence
was
unknown
until
the
invention
of
the
microscope
in
the
17th
century.
The
year
1674,
marks
the
birth
of
microbiology
when
Antony
van
Leeuwenhoek
,
a
Dutch
cloth
merchant,
looked
at
a
drop
of
lake
water
through
a
glass
lens
which
he
had
ground.
What
he
observed
through
this
simple
magnifying
lens
was
an
amazing
sight
since
that
was
perhaps
the
first
time
that
man
ever
had
a
glimpse
of
the
world
of
the
microbes.
Subsequently,
in
a
series
of
letters
to
the
Royal
Society
of
London,
Leeuwenhoek
described
a
variety
of
microorganisms
such
as
protozoa,
algae,
yeast
and
bacteria
and
the
description
was
so
precise
that
it
is
now
possible
to
assign
them
into
specific
genera
without
any
additicnal
description.
Leeuwenhoek
had
little
formal
education
but
his
keen
interest
in
nature
made
him
to
examine
a
variety
of
materials.
Glass
grinding
and
preparation
of
lenses
was
his
hobby
and
this
led
him
to
the
assembly
of
about
400
simple
microscopes.
The
earliest
microscope
that
he
constructed
consisted
of
a
spherical
lens
mounted
on
two
plates
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