Chapter 20
The Origin and Diversification of
Eukaryotes
20.1 Eukaryotes Acquired Features
from Both Archaea and Bacteria
• Eukaryotes that are not plants, animals, or
fungi are called protists
• Scientists believe came from the fusion of
prokaryotes due to endosymbiosis
Eukaryotes arose in several steps
• The origin of a flexible cell surface
• The origin of a cytoskeleton
• The origin of a nuclear envelope
• The appearance of digestive vacuoles
• The acquisition of certain organelles via
endosymbioisis
http://learn.genetics.utah.edu/content/begin/cells/organelles/
Protista Video
20.2 Major Lineages of Eukaryotes
Diversified in the Precambrian
Characteristics of the Protists:
• Range from unicelluar to multicellular
• All are eukaryotic
• Some free-living and some symbionts
• Nearly all are aerobic
• Some are photoautotrophs with chloroplasts;
others are heterotrophs others combine
photosynthesis and eating
Characteristics of Protists
(continued)
• Most have cilia or flagella at some time in their
life cycles
• All can reproduce asexually; others can also
reproduce sexually
• Mitosis occurs in most
• Some have elaborate cells even though
unicellular; e.g., Paramecium
Alveolates have sacs under their
plasma membranes
• Alveolates-possess sacs called alveoli
under their membranes which play a role
in supporting the cell surface
• All are unicellular and most are
photosynthetic
• Dinoflagellates, Apicomplexans, and
Ciliates
Alveolates
http://pinkava.asu.edu/starcentral/microscope/msr/rawdata/viewable/alveolates_1158459360__84w.jpg
Dinoflagellates
• Have protective cellulose plates
• Most have two flagella—one in a longitudinal
groove with distal end free and the other in a
transverse groove that encircles the organism
• Extremely numerous in the oceans
• Most are heterotrophic
Dinoflagellates continued
• Some live as symbionts in invertebrates;
e.g. coral
• 2 genera cause “red tides” and produce a
neurotoxin that can kill fish and paralytic
shellfish poisoning in humans
Figure 28.12 A dinoflagellate
Figure 28.12x1 Dinoflagellate
Figure 28.12x2 Swimming with bioluminescent dinoflagellates
Apicomplexans
• Derive there name from the apical
complex which is a mass of organelles
contained in the apical end (Helps invade
host’s tissues)
• Helps Plasmodium invade tissues to
causes malaria
• Plasmodium and Toxoplasma are
parasites
Apicomplexans
Ciliates
• Named for their hairlike cilia which a like
flagella but shorter
• Have two types of nuclei
• Almost all are heterotrophic
• Most common is the Paramecium
Ciliates
• Contractile Vacuole-A specialized
vacuole that collects excess water taken in
by osmosis, then contracts to expel the
water from the cell
• Digestive Vacuole-An organelle
specialized for digesting food ingested by
endocytosis
Figure 28.14c Ciliates: Paramecium
Figure 28.14x Ciliates: Stentor (left), Paramecium (right)
Figure 28.15x Paramecium conjugating
Paramecium
Excavates began to diversify about
1.5 billion years ago
• Lack mitochondria and lost them as they
evolved
• Shows eukaryotic life is possible without a
mitochondria
• Include: Diplomonads and Parabasalids,
Heteroloboseans, and Euglenids and
Kinetoplastids
Excavates
http://cnx.org/content/m44617/latest/Figure_23_03_02.jpg
Diplomonads and Parabasalids
• Unicellular and lack mitochondria
• Causes contaminated water and diseases
in humans
Diplomonads and Parabasalids
Heteroloboseans
• Has an amoeboid body and can turn into a
life cycle with a flagella
http://pinkava.asu.edu/starcentral/microscope/msr/rawdata/files/trimastigamoeba_ihz.gif
Euglenids and Kinetoplastids
• Unicellular, freshwater organisms
• Some have chloroplasts; the rest ingest food
• If grown in darkness, lose chloroplasts and become
heterotrophic
• Have stored food in pyrenoid in form of a
carbohydrate polymer paramylon
• Bounded by a pellicle which is flexible to allow
changes in shape
Figure 28.03x Euglena
Figure 28.3 Euglena: an example of a single–celled protist
Figure 28.11x Trypanosoma, the kinetoplastid that causes sleeping sickness
Stramenopiles typically have two
unequal flagella, one with hairs
• Include the diatoms and the brown algae
which are photosynthetic
• Also Oomycetes which are not
http://cnx.org/content/m44617/latest/Figure_23_03_08.jpg
Diatoms
• Most numerous unicellular algae in oceans
and are abundant in fresh water
• Have cell walls of silica and many
geometric shapes
• Reproduce both sexually and asexually
Figure 28.17 Diatoms: Diatom diversity (left), Pinnularia (left)
Figure 28.17x Diatom shell
Brown algae
• Both brown and golden brown algae have
chlorophylls a and c
• Range from small forms with simple filaments to
large multicellular forms we call seaweeds
• Provide food and habitat for marine organisms
and are harvested for human food and fertilizer
Figure 28.1d Too diverse for one kingdom: Australian bull kelp (Durvillea potatorum)
Figure 28.20x2 Kelp forest
Figure 28.20x1 Kelp forest
Water molds - oomycetes
• Usually live in water and parasitize fish
• Others live on land and parasitize insects and plants
• One species caused Irish potato famine in 1840s
• Have cell walls of cellulose; fungi have chitin
• Saprobic-feed on dead organic matter
Figure 28.16 The life cycle of a water mold (Layer 3)
Figure 28.16x2 Water mold: Oogonium
Figure 28.x2 Powdery mildew
Rhizaria typically have long thin
pseudopods
• Include Cercozoans, Foraminiferans, and
Radiolarians
• Unicellular and mostly aquatic
• Pseudopods allow for movement
Cercozoans
• Very diverse group with many forms and
habitats
https://ncma.bigelow.org/media/catalog/category/cercozoa.png
Foraminiferans
• Secrete external shells of calcium
carbonate
• Some live as plankton and others live on
the seas floor
• Form much of the world’s limestone
http://gallery.usgs.gov/images/03_27_2014/gkb4Frq11X_03_27_2014/large/Animals_SignsStructuresEtc_Structures_00047.jpg
Figure 28.28 Foraminiferan
Radiolarians
• Have thin pseudopods which are
structured with microtubules
• Help them stay afloat in the ocean
• Well know for when they shed their
endoskeletons
http://micro.magnet.fsu.edu/micro/gallery/radiolarians/radiohead.jpg
Figure 28.27x Radiolarian skeleton
Figure 28.27 Actinopods: Heliozoan (left), radiolarian (right)
Amoebozoans use lobe-shaped
pseudopods for locomotion
• Three groups loboseans, plasmodial slime
molds and cellular slime molds
http://upload.wikimedia.org/wikipedia/commons/b/b3/Chaos_carolinense.jpg
Loboseans
• Small Amoebozoans that feed by
phagocytosis engulfing with the
pseudopod
• Live in the bottom of lakes and ponds
• Most are predators, parasites, or
scavengers
Figure 28.1a Too diverse for one kingdom: Amoeba proteus, a unicellular
"protozoan"
Figure 28.26 Use of pseudopodia for feeding
Plasmodial (acellular) Slime
Molds
• Consist of a multinucleated mass, a
plasmodium
• Phagocytizes decaying plant material
• Develops sporangia during unfavorable
conditions
• Coenocyte-many nuclei enclosed in a single
plasma membrane
Figure 28.29x1 Plasmodial slime mold
Figure 28.1c Too diverse for one kingdom: a slime mold (Physarum polychalum)
Figure 28.29 The life cycle of a plasmodial slime mold, such as Physarum
Figure 28.29x2 Slime mold Sporangia
Cellular Slime Molds
• Consist of individual ameboid cells
• During unfavorable conditions cells
aggregate into pseudoplasmodium
• Sporangium produces spores that release
haploid ameboid cells
Figure 28.30 The life cycle of a cellular slime mold (Dictyostelium)
Figure 28.30x1 Dictyostelium life cycle
Slime Mold Video
• The difference between Plasmodial or
acellular slime molds and cellular slime
molds is that cellular slime molds have
separated nuclei. Plasmodial slime molds
create a mass with multiple nuclei
20.3 Protists reproduce sexually
and asexually
• Protists produce asexually by:
– Binary fission-one cell into two
– Multiple fission- one cell into multiple
– Budding-outgrowth of a new cell from a previous one
– Sporulation-formation of a spore that is able to grow
into a new organism
• Clonal lineages-Asexually reproduced groups
of nearly identical organisms
Some protists reproduce without
sexual reproduction
• Parmecia go through the process of conjugation
• This is when two individuals line up tightly against each
other and fuse
• Genetic material is exchanged creating a micronucleus
• Meiosis and mitosis also take place
• Not a form of reproduction just a sexual process of
genetic recombination
Figure 28.15x Paramecium conjugating
Some protist life cycles feature
alternation of generations
• Alternation of generations-The
succession of multicellular haploid and
diploid phases in some sexually
reproducing organisms
• The haploid organism, the diploid
organism, or both may also reproduce
asexually
• Morphology may or not different in
alternation of generations
• Heteromorphic-the two generations differ
morphologically
• Isomorphic-they do not differ
http://www.quia.com/files/quia/users/lmcgee/protistpictures/AP_Chpt_28_Protists/Alternation-of-generations-.gif
• The gamete producing generation does
not produce gametes by meiosis because
it is haploid
• Specialized cells of the diploid sporeproducing organism, called sporocytes,
divide meiotically to produce four haploid
spores
• Gametes can only produce new organisms
by fusing with other gametes
http://plantphys.info/organismal/lechtml/images/achlyaoogonia.jpg
20.4 Protists Are Critical
Components of Many Ecosystems
http://aquabella4aquariums.com/blog/wp-content/uploads/2013/06/ecosystem101.png
Phytoplankton are primary
producers
http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch11_ecosystems/ecosystem_wp/neriticzone_jonathan_wade/energy_pyramid.gif
Some microbial eukaryotes are
deadly
http://4.bp.blogspot.com/-R-dhf4iQooU/UguBWA19wVI/AAAAAAAABS4/YaR6AYejpy4/s1600/ANOPHELES+MOSQUITOES.jpg
Some microbial eukaryotes are
endosymbionts
Coral Bleaching (Protists dying)
http://media.treehugger.com/assets/images/2011/10/bleached-coral-photo-0001.jpg
We rely on the remains of ancient
marine protists
http://www.agiweb.org/education/energy/images/gasformation.png