Transcript Subtle Accents - Pleasanton Unified School District

Chapter 28
The Origins of Eukaryotic Diversity
By
Henry Hsieh
Perry Huang
Kevin Kim
Joon Park
Period 6
Introduction to the Protists
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Protists existed at least a billion years ago,
before the origin of plants, fungi, and animals
They were the earliest descendants of
prokaryotes
Oldest fossils called acritarchs –
Precambrian objects – about 2.1 billion years
old
Protists are the most diverse of all
eukaryotes
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All protists are eukaryotes
About 60,000 known species of unicellular
protists, few colonial and multicellular
species
Incredibly complex at cellular level because a
single cell would have to perform many
functions
Protists are the most diverse of all
eukaryotes (cont.)
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Protists are metabolically diverse
Most are aerobic in their metabolism and use
mitochondria for cellular respiration
3 categories of nutritional diversity:
1. protozoa (animal-like protists)
2. absorptive (funguslike) protists
3. algae (photosynthetic plantlike protists)
Protists are the most diverse of all
eukaryotes (cont.)
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Most protists are motile, can have flagella or
cilia
- Eukaryotic flagella and cilia are extensions
of the cytoplasm, with bundles of
microtubules covered by the plasma
membrane
Some protists are asexual, others can
reproduce sexually with meiosis and
syngamy (the union of 2 gametes)
Protists are the most diverse of all
eukaryotes (cont.)
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Resistant cells called cysts are formed at
some point in life cycle
Protists can be found almost anywhere with
water
Important constituents of plankton – the
communities of organisms that drift near
water surface that are the bases of most
marine and freshwater food webs
Symbiosis was involved in the genesis of
eukaryotes from prokaryotes
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The endomembrane system of eukaryotic
cells: the nuclear envelope, endoplasmic
reticulum, Golgi apparatus, and related
structures-- may have evolved from
infoldings of the plasma membrane of an
ancestral prokaryote
Endosymbiosis led to mitochondria,
chloroplasts, and other features of eukaryotic
cells
Symbiosis was involved in the genesis of
eukaryotes from prokaryotes (cont.)
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Serial endosymbiosis proposes that
mitochondria and chloroplasts were formerly
small prokaryotes living within larger cells.
All eukaryotes have mitochrondria
Only photosynthetic eukaryotes have
chloroplasts
Mitochondria is proposed to have evolved
before chloroplasts
Protist Systematics and Phylogeny
Monophyletic taxa are emerging from modern research in protist
schematics
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Unicellular eukaryotes assigned to Kingdom
Protista
Later included some multicellular organisms,
such as seaweeds
Kingdom Protista is polyphyletic (members
derived from two or more ancestral forms not
common to all members)
For now, divide into 5 groups of Protists:
Archaezoa, Euglenozoa, Alveolata,
Stramenopila, Rhodophyta.
Fig 28-1. Too diverse for one
kingdom: a small sample of
protists.
Members of candidate kingdom Archaezoa
lack mitochondria and may represent early
eukaryotic lineages
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Several protists lack mitrochondria, leads to
the hypothesis that the lineages of these
organisms diverged before the
endosymbiotic event that gave rise to
mitochondria
Protists that lack mitochondria located in
Kingdom Archaezoa
Diplomonads – subgroup of archaezoans
have flagella, two separate nuclei, no
mitochondria, no plastids, and a simple
cytoskeleton
Members of candidate kingdom Archaezoa
lack mitochondria and may represent early
eukaryotic lineages (cont.)
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A diplomonad parasite called Giardia lamblia
infects human intestines
Giardia and others are living relics of an early
lineage of eukaryotes – evidence indicates
that their genes once coded for mitochondria.
This indicates that their ancestors once
possessed mitrochondria, but have lost them
over evolutionary history.
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Giardia lamblia
Candidate kingdom Euglenozoa
includes both autotrophic and
heterotrophic flagellates
Flagellates- A term that is not used in formal taxonomy.
-Molecular indicates that two groups of flagllates
euglenoids and kinetoplastids make up the monophyletic candidate kingdom
Euglenozoa.
Euglenoids-(Englena and its close relatives) are characterized by an anterior
pocket, or chamber, from which one or two flagella emerge.
Paramylum, a glucose ploymer that functions as a storage molecule, is also
characteristic of euglenoids.
Euglena is chiefy autotrophic, absorbing organic molecules from their
surroundings or engulfing prey by phagocytosis.
The kinetoplastids have a single large mitochondrion associated with unique
organelle, the kinetoplast, that houses extranulear DNA.
Subsurface cavities(alveoli) are diagnostic of
candidate kingdom Alveolata
Another monophyletic candidate kingdom that is emerging from molecular
systematics,
-The Alveolata,
-draws together a group of photosynthetic flagellates ( the dinoflagellates),
-a group of parasites (apicomplexans),
-and a a distinctive group of eukaryotes that move by means of cilia( the
cilates).
-Alveolates have a small membrane-bounded cavities (alveoli) under their
cell surfaces,
functions are unknown; may help stabilize the cell surface and
regulate the cell’s water and ion content
Dinoflagellata (Dinoflagellates)
& Apicomplexa (Apicomplexans)
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Dinoflagellates are abundant components of the vast aquatic pastures of
phytoplankton that are suspended near the water surface and provide the
foundation of most marine and many freshwater food webs. There are also
heterotrophic species of dinoflagellates.
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Apicomplexans are parasites of animals,
 Some cause serious human diseases
The parasites disseminate as tiny infectious cells called sporozoite
Fig 28-13. The two-host life history of Plasmodium , the apicomplexan
that causes malaria. (Colors are not true to life.)
Ciliophora (Ciliates)
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This diverse group of protists is named for their use of cilia to move and feed
Ciliophora (Ciliates) Con.
Most ciliates live as solitary cells in fresh water. In contrast to most flagella,
cilia are relatively short. They are associated with a submembrane system of
microtubules that may coordinate the movement of the thousands of cilia.
Some ciliates are completely covered by rows of cilia, whereas others have
their cilia clustered into fewer rows or tufts.
The specific arrangements adapt the ciliates for their diverse lifestyles. Some
species, for instance, scurry about on leglike structures constructed from many
cilia bonded together.
A unique feature of ciliate genetics is the presence of two types of nuclei,
a large macronucleus and usually several tiny micronuclei.
The genes are not distributed in typical chromosomes but are instead
packaged into a much larger number of small units, each with hundreds of
copies of just a few genes.
The macronucleus controls the everyday functions of the cell by synthesizing
RNA and is also necessary for asexual reproduction.
Ciliates generally reproduce by binary fission,
The sexual shuffling of genes occurs during the process known as conjugation
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Fig 28-15. Conjugation and genetic recombination in Paramecium caudatum .
A diverse assemblage of unicellular
eukaryotes move by means of pseudodia
The three gropus we discuss in this section represent some
of the immense diversity of unicellular eukaryotes that move
and often feed by means of cellular extensions called
pseudpopdia.
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Most of these organisms are heterotrophs that actively seek
and consume bacteria, other protists, and detritus (dead
organic matter). There are also symbiotic species, including
some parasites cause human diseases.
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Little is known about their phylogeny.
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Rhizopods (Amoebas)
Are all unicellular and use pseudopodia to move & to feed.
The cytoskeleton, consisting of microtibules and microfilaments
Functions in amoeboid movement
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Meiosis & sex are NOT known to occur in amoebas.
Reproduce asexually by various mechanisms of cell division.
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Inhabit both freshwater & marine environments and are also abundant in
soils
The majority of amoebas are free-living, but some are important parasites,
including Entamoeba histolytica
Cause amoebic dysentery in humans
(These organisms spread via contaminated drinking water, food, or eating
utensils)
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Actinopods (Heliozoans &
Radiolarians)
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Means “ray foot”
A reference to the slender pseudopodia called axopodia that
radiate from these exceptionally beautiful protists.
Each axopodium is reinforced by a bundle of microtubules
cover by thin layer of cytoplasm
Most actinpods are planktonic
Their projections place an extensive area of cellular surface in
contact with the surrounding water, help the organism float
and feed
Actinopods (Heliozoans & Radiolarians) con.
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Heliozoan(“sun animals”)- living in freshwater.
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Skeletons consist of siliceous(glassy) or chitnous unfused
plates.
Radiolarian(not used in formal taxonomy)-refers to
several groups of mostly marine actinopods w/skeleton
fused into one delcate piece-commonly made of silica
After actinopods die, their skeletons settle settle to the
seafloor, where they have accumlated as an ooze that
is hundreds of meters thick in some locations
Foraminiferans (Forams)
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Are almost all marine.
Most live in sand or attach themselves to rocks & algae,
but some are abundant in plankton
Named for their poruous shells
The shells generally multichambered and consist of
organic material hardened w/calcium carbonate.
Strands of cytoplasm(pseudopodia) extend through the
pores
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Functioning-swimming, shell formation, and feeding.
(Many also derive nourishment from the photosynthesis of
symbiotic algae that live w/in the shells)
Slime molds have structural adaptations and life cycles that
enhance their ecological role as decomposers
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2 groups of protists called slime molds
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Resemble fungi in appearance and lifestyle
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Similarities are convergence
In their cellular organization, reproduction and life cycles
Slime molds depart from the true fungi is partly due to convergent
evolution of filamentous body structure
A morphological adaptation that increase exposure to the environment
and enhances the ecological role of these organisms as decomposers
Slime molds have complex life cycles that are adaptations that
contribute to survival in changing habitats and facilitate dispersat to
new food sources
Plasmodial Slime Molds
(Myxomycota)
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Are more attractive than their name implies.
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Many brightly pigmented, usually yellow or orange, but all are heterotrophic.
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The feeding stage of the cycle is an amoeboid mass called a plasmodium
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Plasmodium are not multicellular
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The cytoplasmic streaming apparently helps distribute nutrients & oxygen
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The plasmodium engulfs food particles by phagocytosis as it grows by
extending pseudopodia through moist soil, leaf mulch, or rotting logs.
If the habitat of slime mold dried out or no food left, the plasmodium ceases
growth and differentiates into a stage of the life cycle that function in sexual
reproduction
Cellular Slime
Molds(Acrasiomycota)
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Pose a semantic question what it means to be an individual organism.
Although the feeding stage of the life cycle consists of solitary cells that
function individually
When food is depleted the cells form an aggregate that function as a
unit
Though the mass of cells resembles a plasmodial slime mold
The distinction is that the cells of a cellular slime mold maintain their
identity and remain separated by their membranes.
Cellular Slime molds also differ from Plas. Slime molds in being
haploid organisms
Cellular Slime molds have fruiting bodies that function in asexual
reproduction.
Most of Cell. Slime mold have no flagellated stages