Important words and concepts from Chapter 28,
Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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(1) Chapter title: The Origins of Eukaryotic
Diversity
(a)
"The more complex a structure, the more structural variation
possible. The origin of eukaryotic cells
was a major breakthrough in the history of biological diversity. Some of the
eukaryotic 'experiments' led to plants,
animals,
and fungi
through divergent lineages of protistan ancestors. We see the products of other
evolutionary experiments in the dazzling diversity of modern protists."
(b)
Note that I will be using a few conventions throughout this document to
distinguish the three main classification systems with which we will be
dealing:
(i)
Five-kingdom system = 5ks =
five-kingdom “sense”
·
in which Protista = paraphyletic
kingdom
(ii)
Three-domain system = 3ds = three-domain “sense”
·
in which Eukarya = monophyletic domain
(c)
Thus, we may differentiate eukaryotic diversity as
|
eukaryote
“kingdoms” in 3ds kingdoms |
equivalent
5ks |
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Rhizopoda (amoebas, polyphyletic) |
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Diplomonadida (Giardia lamblia, Archaezoa*;
flagellates*) |
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Parabasala* (Trichomonas vaginalis*, Archaezoa*; flagellate*) |
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Euglenozoa (Euglenoids, Kinetoplastids, Trypanosoma*,
Archaezoa*; flagellates*) |
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Alveolata (some flagellates*, i.e, dinoflagellates; apicomplexans & ciliates) |
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Stramenopila (water molds, diatoms, golden algae, brown algae) |
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Rhodophyta (red algae) |
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Chlorophyta (green algae,
Viridiplantae*) |
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Plantae
(Viridiplantae*) |
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Mycetozoa (slime molds, Myxogastrida, Dictyostelida) |
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(d)
*terms indicated with an asterisk need not be
memorized
(e)
See Figure 28.8, A tentative
phylogy of eukaryotes
(f)
[the origins of eukaryotic
diversity (Google Search)] [index]
(2) Eukarya = monophyletic domain
(a)
The eukaryotes represent a monophyletic domain, one made up
of the protista, the fungi, the animals, and the plants
(as named according to the five-kingdom system—5ks)
(b)
See Figure 28.6, Traditional
hypothesis for how the three domains of life are related
(c)
Note, however, that a major caveat to this state are considerations of
horizontal transfer that occurred both between free-living prokaryote and
eukaryote lineages and which occurred between the eukaryote nuclear DNA and the
DNA of endosymbionts (mostly from the latter to the former)
(d)
See Figure 28.7, An alternative
hypothesis for how the three domains of life are related
(e)
[eukaryotes monophyletic
(Google Search)]
(The Tree of Life)] [index]
(3)
Kingdom Protista (protists)
(a)
Kingdom Protista (in the 5ks)
consists of the single-celled eukaryotes as well as a variety of not very
morphologically complex multicellular eukaryotes
(b)
“All protists are eukaryotes, but
protists are so diverse that few other general characteristics can be cited
without exception. In fact, protists vary in structure and function more than
any other group of organisms… at the cellular level, many protists are
exceedingly complex—the most elaborate of all cells. We should expect this of
organisms that must carry out within the boundaries of a single cell all the
basic functions performed by the collective of specialized cells that makes up
the bodies of plants and animals.” p.
520, Campbell et al., 1999
(c)
See Figure 28.1, Too diverse
for one kingdom: a small sample of protests
(d)
See Figure 28.2, The kingdom
Protista problem
(e)
[kingdom protista (Google Search)]
[images of protists
(Biology 122 Laboratory
– Southwest Missouri State
Univerisity] [index]
(4) Protista = paraphyletic taxon
(a)
Kingdom protista in the five-kingdom system
is a paraphyletic kingdom, meaning that there
exist a number of taxa (kingdoms) that are not included among the protists but
nevertheless descended from protists (5ks)
(b)
See Figure 28.8, A tentative
phylogy of eukaryotes
(c)
Keep in mind that while plants (as well as fungi, and animals)
essentially are modified protists, nevertheless plants (as well as animals and
fungi) will be considered in subsequent chapters
(d)
[protista paraphyletic
(Google Search)]
[index]
(5) Nutrient-acquisition categories ( engulfers vs. nutrient
absorbers vs. algae)
(a)
We can differentiate the members of Kingdom Protista into three non-clade nutrient-acquisition categories:
(i)
Engulfers: Single-celled eukaryotes that obtain their nutrients by engulfing
particles of food (the protozoa); these include:
·
Amoeba (Rhizopoda) including Forams (Foraminifora),
·
Ciliates (Ciliophora)
·
Slime molds (Myxogastrida and Dictyostelida in Mycetozoa)
(ii)
Nutrient absorbers: Non-fungus, non-animal eukaryotes that obtain their nutrients by
absorption across their cell membrane (the fungus-like protists); these
include:
·
Diplomonads such as Giardia lamblia (Diplomonadadida)
·
[???Trichomonads (Parabasala)???]
·
Euglena (Euglenoids in Euglenozoa)
·
[???Dinoflagellates (Dinoflagellata in Alveolata)???]
·
Water molds (Oomycota)
(iii)
Algae:
Non-plant photosynthetic eukaryotes (the algae)
·
Euglena (Euglenoids in Euglenozoa)
·
Dinoflagellates (Dinoflagellata in Alveolata)
·
Diatoms (Bacillariophyta in Stramenopila)
·
Golden Algae (Chrysophyta
in Stramenopila)
·
Brown Algae (Phaeophyta
in Stramenopila)
·
Red Algae (Rhodophyta)
(b)
“Though commonly used, the terms protozoa and algae have
no basis in phylogeny and no significance in taxonomy.” p. 521, Campbell et al., 1999
(c)
[“When Robert Whittaker popularized the five-kingdom system of
classification in 1969, he assigned unicellular eukaryotes to Kingdom Protista.
The trend during the 1970s and 1980s was to expand the boundaries of Kingdom
Protista to include some groups of multicellular organisms, such as seaweeds,
classified in earlier versions of the five-kingdom system as either plants (in
the case of seaweeds) or fungi. These taxonomic transfers were based mainly on
comparisons of cell structure and details of life cycles. In its expanded form,
Kingdom Protista also encompassed phyla of funguslike organisms, such as the
forms known as slime molds and water molds, which may have their closest
relatives among the unicellular eukaryotes called amoebas. (Slime molds are
fungus-like only in the sense that a whale is fishlike; the resemblance is due
to convergent evolution of morphological adaptations, not to common ancestry.)
The tendency was to treat Kingdom Protista as the taxonomic home for all
eukaryotes that did not fit comfortably into the definitions of plants, fungi,
and animals.” p. 524, Campbell
et al., 1999]
(d)
[(Google Search)]
[index]
(6) Protista general characteristics
(a)
Protists are
(i)
Mostly aerobic respirators
(ii)
Mostly motile during at least some stage
(iii)
Mostly chemoheterotrophs (algae excepted)
(iv)
Mostly aquatic (or, at least, favoring moist
conditions)
(vi)
and, of course, are all eukaryotic
(b)
Note that part of understanding protist biology will be to understand
protist life cycles—be prepared to learn not just the names (and basic
characteristics) of various protist taxa, but also to learn, at least in
outline, various protist life cycles
(c)
[protista general
characteristics (Google Search)] [index]
(7)
Protists are mostly aerobic respirators
(a)
Most protists are aerobic respirators, possessing either endosymbiotic mitochondria or analogous intracellular bacteria
(b)
Exceptional are the Archaezoa which are protists that lack
mitochondria
(c)
[(Google Search)]
[index]
(8)
Prostists are mostly motile
(a)
Most protists possess a flagella, cilia, or pseudopods during at least some portion of
their life histories so consequently are motile
during at least some portion of their life histories (Rhodophyta, in
particular, are excepted)
(b)
This contrasts with nearly all fungi
which never possess flagella or cilia
(c)
[(Google Search)]
[index]
(9)
Protists are mostly chemoheterotrophs
(a)
Most protists are chemoheterotrophs
(b)
Exceptions include the various algae
(c)
Additionally, there are protists, the mixotrophs, that
combine chemoheterotrophy with photoautotrophy (e.g., Euglena) using chloroplasts to gather light when that is available and
absorbing nutrients when light is not available
(d)
Animals
and fungi,
too, are chemoheterotrophs
(e)
[(Google Search)]
[index]
(a)
Mixotrophs combine photosynthesis and chemoheterotrophic modes of
nutrient acquisition; that is, they obtain their energy both from photons and
from reduced carbon compounds, particularly the latter when the sun is not
shining, and vice versa
(11)
Protists diplay a great diversity of reproductive strategies
(a)
Reproductive strategies of protists include
(i)
Asexual (i.e., reproducing solely via mitosis)
(ii)
Sexual with no mitosis in the diploid state
(iii)
Alternation of generations
(b)
“Among eukaryotes, sexual life cycles are the most
varied among the protists.” p. 524, Campbell et al.,
1999
(c)
Sexual protists display syngamy and the life histories of many
protists are further complicated by an ability to differentiate into cysts
(d)
Note that part of understanding protist biology will be to understand
protist life cycles—be prepared to learn not just the names (and basic
characteristics) of various protist taxa, but also to learn, at least in
outline, various protist life cycles
(e)
[protist reproduction
(Google Search)]
[index]
(a)
Syngamy is the fusion of gametes to form the
diploid zygote (which founds the sporophyte
generation in plants
and some algae, or the diploid stage in animals)
(b)
[syngamy (Google Search)]
[index]
(a)
Many protists can form cysts which are cell types that are resist harsh
environmental conditions such as drying out or long periods without
reproduction (i.e., no mitosis)
(b)
Supplement: Below shows as Giardia cyst undergoing excystation,
i.e., conversion from the resistant state (cyst, on left) to the vegetative
state (trophozoite, on right):
(d)
[protist cysts (Google Search)]
[index]
(14)
Protists are mostly aquatic (benthic, planktonic)
(a)
Protists are adapted for the most part to lives spent either in aqueous
or very wet environments; that is, the kingdom protista (5ks) niche
is a wet one
(i)
Some protists attach to non-floating aqueous surfaces, e.g., rocks or
sand on the bottom of a body of water; these are described as benthic
(ii)
Some protists float within bodies of water; these are described as
planktonic
(iii)
The parasitic protists inhabit the body fluids of animals and others
can serve as plant pathogens; we would describe these as non-free living as
well as parasitic (though in some cases the parasites are actually carnivores:
killing their hosts before eating them)
(b)
[protist benthic, protist planktonic
(Google Search)]
[index]
(15)
Protists are important aquatic producers
(a)
“As a large group of autotrophs, the eukaryotic algae are extremely
important ecologically. Phytoplankton (planktonic algae, along with the
prokaryotic cyanobacteria) are the bases of most marine and freshwater food
webs. Accounting for at least half the protosynthetic production of organic
material globally, they support an enormous abundance and diversity of
heterotrophic protists and animals.” p. 521, Campbell
et al., 1999
(b)
[(Google Search)]
[index]
(a)
Two things distinguish eukaryotes from prokaryotes
(i)
Internal membranes (e.g., the endomembrane system)
(ii)
Endosymbionts (e.g., mitochondria and chloroplasts)
(b)
The endomembrane system includes, of course, the cell nucleus; all
extant eukaryotes possess an endomembrane system and a cell nucleus
(c)
These membranes probably were derived from infoldings of cytoplasmic membrane of the ancestral
prokaryote
(d)
See Figure 27.8, Specialized
membranes of prokaryotes
(e)
The latter (the endosymbionts) represent co-evolved, cytoplasmic-living, gram-negative bacteria
(f)
See Figure 28.4, A model of
the origin of eukaryotes
(g)
[origin of eukaryotes
(Google Search)]
[index]
(17)
(a) The endosymbiotic theory is the idea that mitochondria and chloroplasts both descended from free-living, ancestral bacteria<