Download Prokaryotes

This week in lab: sampled trees in 2 habitats at Green Oaks,
‘Old Growth’ & Spoil Banks
- your assignment:
1) Use the supplied data & your lab handout to
calculate Shannon-Weiner Diversity Indices
& Schoener’s Community Similarity Index
2) Answer the questions on assignment sheet (back
of room, or on the course website)
Last day… we were discussing the major changes occurring
during the history of life, including mass extinctions
Included the Cretaceous-Paleogene (K-T) extinction event
that wiped out dinosaurs and much more
Luis and Walter Alvarez
The K-T extinction was not the worst ever…
- late in Permian, massive volcanic eruptions causing
lava flows, ash, and cooling of climate
- extensive glaciation
- turn-over of ocean waters brings oxygen depleted
water, CO2 and hydrogen sulfide to surface
Extinction of most living species (>90% of marine spp.),
and end of Paleozoic era.
History of life characterized by great changes in flora
and fauna due to extinction & evolution
- response to mobile continents & constantly
changing climate
Fossil record incomplete, but does document many
sweeping changes in living things
*Required*
reading: Chapt.
25, pp. 507-524
This long history of life has resulted in an enormous
diversity of organisms on the planet
- we will try to survey some of this diversity...
Traditionally, organisms classified as plants or animals
(Kingdoms Plantae & Animalia)
- but many species do not fit readily into these categories...
- a five kingdom system became popular after 1969
- but still does not reflect relationships well, or do justice to
diversity of smaller organisms...
A three domain system is a starting point for organizing
all of these species: Bacteria, Archaea, & Eukarya
The first two domains are traditionally grouped as
‘prokaryotes’:
- simpler internal structure than eukaryotic cells
(no nucleus or other membrane enclosed organelles
such as mitochondria)
Generally tiny (1-5 m),
though some only... tiny
Found almost everywhere...
- soil, water, in & on other organisms
- places too hot or cold or inhospitable for most life
- usually do require moisture
Most ‘prokaryotes’ are unicellular, a few may be colonial
- come in various shapes, especially cocci, bacilli, and
spiral forms
Normally have a cell wall - protects, maintains shape &
prevents bursting in hypotonic conditions
Cell walls contain peptidoglycan (sugars linked by
peptides)
- thick outer layer in gram positive bacteria, thinner layer
between membranes in gram negative
Some are covered with sticky capsule (polysaccharide or
protein)
- helps stick to surfaces, protects
Some use fimbriae (short, hairlike) to stick to each other
or surface
May also use pilus (pl. pili) to hold on, or to exchange DNA
- horizontal gene transfer
About 50% are capable of directional motion,
sometimes ‘fast’
- rotation of basal apparatus moves flagella
Taxis: movement toward (or away from) chemicals,
conspecifics, etc.
Lack organelles, but may have membranes from infoldings
of plasma membrane
‘Prokaryotes’ have single, circular ‘chromosome’
- few associated proteins
May also have smaller DNA rings called plasmids that
often carry ‘specialized’ genes (e.g. antibiotic
resistance)
Reproduction is by binary fission, some can divide every
20 minutes
Under unfavourable conditions, some spp. produce
endospores
- chromosome copied & surrounded by tough wall,
water removed, spore can remain dormant for centuries
‘Prokaryotes’ exploit a wider range of resources than all
eukaryotes combined
‘Prokaryotes’ may be obligate aerobes (require O2 for
aerobic respiration), facultative anaerobes (use
O2 when available, or fermentation if not) or
obligate anaerobes (must use fermentation or
anaerobic respiration)
All organisms require nitrogen to make proteins, etc.,
but only certain prokaryotes can fix N2 to
produce ammonia NH3 (nitrogen fixation)
Some ‘prokaryotes’ form colonies, and may show
cooperation or specialization
- some cyanobacteria have specialized cells for
photosynthesis and nitrogen fixation
Bacteria that produce dental plaque grow as colony to
form resistant coating
Discussing ‘prokaryotes’ as if one uniform group, but far
from true...
- paraphyletic grouping, Archaea closer to eukaryotes than
bacteria
Bacteria & Archaea
share some ancestral
traits
Archaea & Eukarya
share some derived
traits
Each domain may also
show some unique
traits
Each group also
shows great
diversity
within...
Archaea seem to be less abundant, and often found in
extreme environments where other organisms
cannot live (e.g. thermophiles, halophiles,
methanogens), but new types still being found