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AP Biology
LECTURE NOTES: Chapter 28
Protists
FIGURE 28.1 – Too diverse for one kingdom: though systematists have split the five-kingdom system’s
Protista into many kingdoms, “protist” is still a convenient informal term for the great diversity of eukaryotes
that are NOT plants, fungi, or animals.
Most protists are unicellular
• And some are colonial or multicellular
• Protist habitats are also diverse including freshwater and marine species
Protists, the most nutritionally diverse of all eukaryotes, include
• Photoautotrophs, which contain chloroplasts
• Heterotrophs, which absorb organic molecules or ingest larger food particles
• Mixotrophs, which combine photosynthesis and heterotrophic nutrition
Reproduction and life cycles are also highly varied among protists, with both sexual and asexual species
• Mitosis occurs in all protists
• Some protists are exclusively asexual
• Other can also reproduce sexually or at least employ the sexual process of meiosis and syngamy
– Syngamy is the process of cellular union during fertilization
FIGURE 28.4 – The origin and early diversification of eukaryotes. Among the most fundamental questions in
biology is how the complex eukaryotic cell evolved from much simpler prokaryotic cells.
How did compartmental organization of the eukaryotic cell evolve from the simpler prokaryotic condition?
• In one process, the endomembrane system – the nuclear envelope, ER, Golgi, and related structures –
may have evolved from specialized infoldings of the prokaryotic plasma membrane.
• Another process, called endosymbiosis, probably led to mitochondria, plastids, and some other features
of eukaryotic cells.
Mitochondria & plastids evolved from endosymbiotic bacteria:
• Plastids are a general term for the class of eukaryotic organelles that includes chloroplasts
• Chloroplasts and mitochondria are descendants of cyanobacteria and aerobic, heterotrophic prokaryotes,
respectively, that took up residence within evolving eukaryotic cells.
There is now considerable evidence that much of protist diversity has its origins in endosymbiosis. The plastidbearing lineage of protists evolved into red algae and green algae. On several occasions during eukaryotic
evolution, Red algae and green algae underwent secondary endosymbiosis, in which they themselves were
ingested.
The evidence for the endosymbiotic origin of chloroplasts and mitochondria include:
• Both chloroplasts and mitochondria are the appropriate size to be descendents of bacteria
• The inner membranes of both have several enzymes and transport systems resembling those of modern
prokaryotes
• Both replicate by a process similar to binary fission
• Both contain their own separate genome of a single, circular DNA molecule
• The ribosomes of chloroplasts and mitochondria are more similar to prokaryotic ribosomes than
eukaryotic ribosomes
AP Biology
LECTURE NOTES: Chapter 28
Protists
TABLE 28.1 – The origin and early diversification of eukaryotes. Among the most fundamental questions in
biology is how the complex eukaryotic cell evolved from much simpler prokaryotic cells.
Structural and biochemical adaptations help seaweeds survive and reproduce at the ocean’s margins.
• Seaweeds include the thallus-forming marine species among the brown, red, and green algae.
Some algae have life cycles with alternating multicellular haploid and diploid generations.
• Haploid gametophytes and diploid sporophytes take turns producing one another.
Multicellularity originated independently many times.
• In addition to seaweeds and other multi-cellular protists, multicellularity evolved in the ancestors of
plants, fungi, and animals.
Most protists are classified by their method of obtaining nutrients:
• Animal-like protists are heterotrophs
• Plant-like protists photosynthesize
• Fungus-like protists are parasites or decomposers
FIGURE 28.11, 28.13, 28.14, 28.15 - Diversity of Animal-Like Protists
Phylum Name
Common Name
Traits/Characteristics
1. Rhizopoda
Amoeba
2. Actinopoda
Foraminiferans
Actinopods
3. Zoomastingina
Zooflagellates
4. Ciliophora
Ciliates
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5. Apicomplexa
Sporozoa
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Sarcodines (amoeboid-like movement)
use pseudopods (false feet) for movement
have highly perforated shell of calcium carbonate
move with cytoplasmic extensions “ray foot” that go through the
perforated shell
fossil shells form in marine sediments
many are planktonic
flagellated protozoans
undulating membranes
mostly unicellular
free-living, parasitic, or endosymbionts
Ex:
• Giardia (from feces infected water)
• Trichomonas vaginalis (vaginal infections)
• Trichonymphs digest cellulose in termites
• Trypanosoma (parasitic) causes African Sleeping Sickness
use cilia to move and feed
most live in fresh water – solitary
2 or more nuclie
• macronucleus with 50 or more copies of genome
• micornuclei that are requried for conjugation
extremely complex – contractile vacuoles used for water balance,
mouth, anal pore
Ex:
• stentors and paramecium
parasitic, form sporozoites (infectious cells that have specialized
structures at the apex to help penetrate into host)
Ex:
• Plasmodium (causes malaria)
AP Biology
LECTURE NOTES: Chapter 28
Protists
FIGURE 28.21, 28.23 & 28.24 - Diversity of Algae & Plant-like Protists
Phylum Name
Common Name
Traits/Characteristics
1. Euglenophyta
Euglenoids
2. Dinoflagellata
Dinoflagellates
3. Bacillariophyta
Diatoms
4. Chrysophyta
Golden Algae
5. Chlorophyta
Green Algae
6. Phaeophyta
Brown Algae
7. Rhodophyta
Red Algae
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unicellular with 1-3 flagella
common in freshwater
has pellicle (protein strips that wrap over membrane)
eyespot for phototaxis
photoautotrophs, but some can become heterotrophs w/out light
cause algal blooms – harmful to freshwater systems
major component of photosynthetic phytoplankon
2 flagella – spinning movement
blooms cause red tides (toxic from xanthophylls pigment)
can produce toxins that kill fish
some are bioluminescent
glass shells of silica
freshwater/marine plankton – extremely abundant
major constituents of marine sediment
asexual reproduction is most common
major primary producers of fresh water & marine ecosystems
yellow/brown carotene and xanthophylls pigment
2 flagella
unicellular or colonial
freshwater and marine plankton
most closely related to land plants
both chlorophyll a, b, and carotenoids (like land plants)
have cellulose in cell walls (like land plants)
use starch to store polysaccharides (like land plants)
single celled and colonial
most produce flagellated cells at some part of life cycle
can be very diverse (volvox colonies, ulva sea lettuce)
some form mutualistic relationships with fungi (lichens)
complex sexual and asexual life cycles
• isogamous – 2 flagellated gametes of equal size
• anisogamous – gametes differ in size
• oogamous – non mobile large egg w/ small flagellated male
multicellular
flagellated sperm
fucoxanthin (brown pigment)
most have alternation of generations life cycle
• thallus = body
• holdfast = rootlike system
• stripe = stemlike system
• blades = leaf like organs
Ex: giant kelp
multicellular
phycobilin (red accesory pigment) – makes red algae efficient at
greater ocean depths because pigment is specialized for absorbing
blue wavelengths of light for photosynthesis
no flagellated stage; dependent on ocean currents for fertilization
AP Biology
LECTURE NOTES: Chapter 28
Protists
FIGURE 28.16, 28.29 & 28.30 - Diversity of Fungal-like Protists
Phylum Name
Common Name
Traits/Characteristics
1. Acrasiomycota
Cellular Slime Molds
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2. Myxomycota
Plasmodial Slime Molds
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3. Oomycota
Water Molds
Downey Mildews
White Rust
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fungal-like and amoeba-like characteristics
unicellular amoeboid feeding stage
multi-cellular slug-like aggregation stage – forms fruiting
bodies that produce “spores” that germinate into amoebas
cAMP released by amoebas that experience food deprivation
which signals the aggregation stage
brightly pigmented yellow or orange
plasmodium is an amoeboid feeding mass that is NOT
multicellular; it is unicellular, but multinucleated (caused by
multiple mitotic divisions w/out cytokinesis)
plasmodium dries up and forms fruiting bodies
• meiotic division within the fruiting bodies create
haploid spores that are amoeboid or flagellated.
fertilization allows for plasmodium formation
parasitic or saprobes (obtain energy from dead matter)
closest to actual fungi
have mycelium (main body) made up of hyphae (threadlike
filaments that secrete enzymes for digestion)
they are coenocytic (have many nuclei within a single cell) but
lack the “cross walls” or septa which partition the filaments
into cellular components, as found in true fungi.
Ecology of Animal-Like Protists
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Not so Good: Can be parasitic/cause disease
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Malaria, African Sleeping Sickness, Cryptosporidium
Good: Symbiosis
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Termites have beneficial animal like protists called Trichonympha in their stomachs
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Break down cellulose in wood so termites can use it as food
Ecology of Plant-Like Protists
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Most unicellular species beneficial
Act as producers in the marine food chain
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Form Phytoplankton for consumer organisms to eat
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Approx. ½ of the photosynthesis on earth - produce large amount of oxygen
Symbiosis: Coral Reefs, Clams
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Provide food via photosynthesis, receive a home
Ecology of Fungi-Like Protists
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The ecological impact of oomycetes can be significant
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Phytophthora infestans causes late blight of potatoes – Irish Potato Famine
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Overgrowth of water mold caused by wet and cool conditions
Slime molds and water molds are the MOST important recyclers of organic material
Why is the earth not littered with dead organisms?
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Tissues broken down by Fungi Like Protists and other decomposers
Beneficial Aspects of Algae
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Food for humans, food for invertebrates and fishes
Animal feed
Soil fertilizers and conditioners in agriculture
Treatment of waste water
Diatomaceous earth (= diatoms)
Chalk deposits
Phycocolloids (agar, carrageenan from red algae; alginates from brown
algae)
Drugs
Model system for research
Phycobiliproteins for fluorescence microscopy
Detrimental Aspects of Algae
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Blooms of freshwater algae
Red tides and marine blooms
Toxins accumulated in food chains
Damage to cave paintings, frescoes, and other works of art
Fouling of ships and other submerged surfaces
Fouling of the shells of commercially important bivalves