Download Part 3 (Archaea - Updates Book)

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Unit A: Continuity of Life
Chapter 1:
Classification of Living Things
Lesson 1 – Part 3:
How Do Scientists Classify Organisms?
E.
Archaea
1. Important features:
a. Archaea are always unicellular, meaning they are one-celled.
1) Archaea are usually under one micrometer in length.
2) They come in various shapes:
a) Some are cocci and bacilli shapes, but there are also
b) odd shaped archaea, including triangular- and square-shaped:
Left: Image of an example of postage stamp-shaped
archaea, Haloquadratum walsbyi.
Below: Image of triangular archaea, Haloarcula japonica.
(These, oddly enough, will turn spherical if the
magnesium concentrate levels are low enough.)
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3) Archaea may also have other features similar to bacteria, such as
a) a cell membrane
b) a cell wall (common to nearly all archaea)
c) cytoplasm
d) flagellum
b. Archaea are prokaryotic, like bacteria.
c. Archaea are often extremophiles, meaning that they can be found living in
extreme environments not usually suitable for life; examples of places where
archaea have been found thriving include:
1) mud pots and hot springs (including those of Yellowstone National Park)
2) deep layers of marine sediment,
3) hydrothermal vents (hot springs on the floor of the ocean often near midocean ridges),
4) hot, dry deserts,
5) highly saline lakes such as the Great Salt Lake and the Dead Sea,
6) buried under kilometers of ice in Greenland,
7) in the rock of the Earth's crust, kilometers below the surface.
d. Other places archaea are commonly found—and are often important to
biology and ecology include:
1) in the guts of animals (where they produce methane), including
a) many ruminants (animals like cows; plant-eaters)
b) human beings (where they aid in digestion)
2) in wetlands (they are producers of methane marsh gasses)
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2. Although Archaea are similar to bacteria in appearance, they are
different from bacteria in several important ways:
a. Archaea differ in their genetic make-up from other life forms.
1) The DNA of archaea is not closely related to either their fellow
prokaryotes, the bacteria, nor the eukaryotes (the category humans fall
into); they are in a category all by themselves.
2) Analysis of DNA sequences of known archaea reveals three distinct groups
of Archaea (some argue that these should be kingdoms within the Archaea
domain):
a) Euryarcheota - the best known; includes many methane-producers
and salt-loving archaeans.
b) Crenarcheota – some of these species live at the highest
temperatures of any known living things—including in water hot
enough to boil! (A variety have recently been discovered growing in soil
and water at more moderate temperatures, however).
c) Korarcheota are only known from their DNA sequences—nothing more
is known about them (they have only recently been discovered).
b. Archaea differ in their chemical make-up from other lifeforms.
1) While archaea have many features that look similar to those found on
other cells, these features are chemically different from those of bacteria
or eukaryota.
2) Specific differences between archaea and either bacterial or eukaryotic
cells include:
a) Cell membranes of archaea are comprised of markedly different
molecules and are physically constructed quite differently at the
chemical level.
b) Cell walls of archaea are not made of cellulose (like plant cells) or
chitin (like fungi), but of other substances altogether.
c) The process of photosynthesis, when it occurs in archaea, differs from
that of plant or the various bacterial versions of photosynthesis.
Modified from material found at: Boundless. “Methane-Producing Archaea: Methanogens.” Boundless Microbiology. Boundless, 21 Jul. 2015. Retrieved 27 Sep. 2015 from
https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microbial-evolution-phylogeny-and-diversity-8/euryarchaeota-111/methane-producing-archaea-methanogens-57610785/, http://www.ucmp.berkeley.edu/archaea/archaeamm.html, http://www.cell.com/trends/microbiology/abstract/S0966-842X%2805%29000727?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0966842X05000727%3Fshowall%3Dtrue, http://link.springer.com/article/10.1007%2FBF01955151, and
http://tolweb.org/Archaea/4