Chapter
27
Animations
Art
Unit 5: The Evolutionary History of Diversity
Bacteria and Archaea
Review
Most
prokaryotes
are microscopic, and can be found almost
anywhere.
The most common
shapes
are
(cocci),
(bacilli), and
.
Many bacteria exhibit
, the directional movement in response to a
, by propelling themselves
with
.
The prokaryotic genome is usually a circular
ring
of DNA located in a
region; some also have smaller rings of DNA called
.
Prokaryotic cells
lack
. The cell wall of many prokaryotes is covered by a
protective
, and many also
form
in harsh conditions.
Review.
Response to
stain classified bacterial species into two groups based on amount of
in the
cell
: gram-
and gram-
.
Molecular analysis has now revealed several
among the gram–negative
prokaryotes,
while another group is now assigned its own
domain
of
.
Many archaea live in extreme conditions:
thrive in
hot
environments,
live in
saline
environments, and
live in
swamps.
The gram-
bacteria
constitute their own clade.
Gram-
bacteria include
cyanobacteria,
and
, which
includes
E. coli
and the nitrogen fixing
Rhizobium
.
Prokaryotes play crucial roles in the biosphere.
Most are
and recycle nutrients in the ecosystem.
Some are
nitrogen
and convert atmospheric
(N
2
) to an organic form such as
(NH
3
) that can be used by other organisms.
Cyanobacteria
are
and release oxygen for aerobic organisms to use.
In the cyanobacterium
Anabaena
,
cells and
-fixing cells exchange metabolic products in a
cooperative
.
Some prokaryotes are human pathogens, such as the
bacterium that causes
Lyme
disease. Pathogenic prokaryotes release two types of
.
are secreted
, such as those that cause
anthrax
and
cholera.
are lipopolysaccharide components of some bacterial
which causes typhoid fever,
.
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Nov 15, 2008
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