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Protists: Algae
Lecture 5
Spring 2014
Meet the algae
1
Protist Phylogeny
“Algae” - Not
monophyletic
What unites them as
a group?
• Range from
unicellular to
multicellular
• From phytoplankton
to kelp forests
Fig. 28.3
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Primary & Secondary Endosymbiosis
• Primary
Endosymbiosis
Fig. 28.2
Secondary Endosymbiosis
Fig. 28.2
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Endosymbiosis
• A second case of primary
endosymbiosis?
– Paulinella chromatophora
• Supergroup
Rhizarian
• Cerozoans
Fig. 28.19
Photosynthetic pigments in chloroplasts
Chlorophyll a
• Required for
photosynthesis
Accessory pigments
• Broadens the spectrum of light
that can be absorbed
– Chlorophyll b
– Chlorophyll c
– Carotenoids (e.g. fucoxanthin,
phycoerythrin, others)
• sunscreen, coloration
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Photosynthetic Pigments in Chloroplasts
Why would so
many different
pigments
evolve?
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Algae: Ecological Roles
• Primary productivity
– Productivity – amount of biomass produced in a given
area during a given period of time
Fig. 28.27
20% of world’s
photosynthesis
30% of world’s
photosynthesis
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Algae: Ecological Roles
• Carbon cycling
– carbon sink
• Various mutualistic
relationships
Fig. 54,17
Algae: Ecological Roles
Algal blooms
What limits growth of
algae?
Factors
• Warm surface temperatures
• High nutrients
• Low salinity
Algal blooms
• Excessive growth of algae
• “red tides”, “brown tides”
• Toxins
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Algae: Ecological Roles
• Iron fertilization & diatoms
Fig 28.28
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Euglenids
Supergroup Excavata
Clade Euglenozoa
Key traits of clade:
• Typically two flagella, one
long, one short
– crystalline rod in flagella
Fig. 28.5
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Fig. 28.7
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Euglenids
Fig. 28.7
Phylum Euglenophyta
~ 900 described species
• Unicellular
• Photoautotrophs or
mixotroph
– Light detector and eyespot
• Most freshwater
• Important part of food chain
• Key trait of Phylum
– Flagella (1 or 2) emerge from pocket at one end of cell
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Dinoflagellates
Supergroup Chromalveolata
Clade Alveolata
Key trait of clade: membrane
bound sacs (alveoli) beneath
the plasma membrane
Phylum Dinophyta
• ~4000 described species
• Photosynthetic, mixotrophic
& heterotrophic
• Unicellular
• Solitary & colonial
Fig. 28.8
Fig. 28.8
Dinoflagellates
Phylum Dinophyta
Key traits:
• 2 flagella
– positioning of flagella causes organism to spin
• Plates of cellulose – “armored”
Fig. 28.9
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Dinoflagellates: Ecological Roles
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• Marine and freshwater phytoplankton
– Important primary producer
• Some mutualistic
– zooxanthellae - symbiotic dinoflagellate
• lacks armored plates
– Corals, sponges, jellyfish, octopuses
and squids, snails, etc.
Cross section of coral
polyp w/zooxanthellae
• Very important in coral reef ecosystems
• “red tides”
– Carotenoid pigments
– 20% of known dinoflagellates release toxins
Coral
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Diatoms, Golden & Brown Algae
Supergroup Chromalveolata
Clade Stramenopila
Key traits of clade
• 2 flagellum
– 1 long with “hairy” (hollow
tubes) projections, one short
– May be only reproductive
cells or lost
Fig. 28.12
What non-photosynthetic protist
belongs to the Stramenopiles?
Diatoms
Phylum Bacillariophyta
~100,000 species
• Unicellular
• Solitary or colonial
• Typically 20-200 microns in diameter or length
– Up to 2 millimeters long
• No flagella
• Secrete intricate shell
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Diatoms
• Glass-like wall (shell, test)
– Hydrated silica in organic
matrix
– Asexual reproduction limits
Fig. 28.13
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Diatoms
Lifestyle:
• Free floating, can sink or adjust depth
– Oils, amount of silica accumulated,
projections
– no flagella
• Also grow on whales, turtle shells, aquatic
plants, etc
• few terrestrial
• Carbon sink
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Diatoms
Resting spores (cysts) - resistant stage
• Metabolically inactive spores
– Stored photosynthetic products
– Tough thickened cell walls
• Sink to the bottom of the sea
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Golden Algae
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Phylum Chrysophyta
• ~1,000 described species
• Unicellular & solitary (most)
• Colonial (some)
– Some w/silica covering
• Cells w/two flagella,
attached near one end
• Some mixotrophic
• Yellow & brown carotenoids
Fig. 28.14
Golden Algae
Lifestyle
• Many planktonic
• Most freshwater, some marine
• Asexual & sexual reproduction
Resting spores (cysts)
• Resistant stage
• Cyst made of silica
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Brown Algae
Phylum Phaeophyta
~ 1500 described species
• Multicellular
• Mostly marine
• Brown carotenoids
• “seaweed”
• More complex cellular structure than other algae
– Specialized tissues, organs
• From microscopic to huge (kelp forests)
• Among the largest photosynthetic organisms
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“Seaweeds”
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• Incl. brown, red & green red algae
• Thallus (algal body that is plantlike)
Flotation bladder
Holdfast
Brown Algae
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Many species live in the
marine intertidal zone
Cell walls of cellulose and
alginic acid
– Alginic acid = gel-forming
polysaccharides
– Protection from waves &
dehydrtion
Brown & green algae
Brown Algae
Kelp forests
• Deeper water
• Primarily temperate
zone
• Generally not free
floating
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Red algae & green algae
• Supergroup Archaeplastida
• Closest living relatives to land plants
• 475 million years ago green algae and land
plants diverged
• Viridiplantae?
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Red Algae
Phylum Rhodophyta
~ 6,000 species
• Most multicellular
• Many filamentous
• Key traits
• Accessory pigment
phycoerythrin (red
carotenoid)
• No flagella
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See Fig 28.20
Red Algae
Lifestyle
• Mostly marine
• Abundant in tropical waters
• Present in deep water
– Color varies by depth
Coralline algae
Reef-building algae
• Calcarous
– (calcium carbonate cell walls)
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Green Algae
•
•
•
•
•
•
Phylum Chlorophyta and Charophyceans
~ 17,000 described species
Key traits:
Chloroplasts similar to those found in plants
Chlorophyll a & b
Color not masked by carotenoids, so green
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Green Algae
Lifestyle
• Highly diverse
• Freshwater and marine
– Some planktonic
• Some terrestrial
– Chlamydomonas nivalis
• Mutualisms
– Lichen
– Sponges, freshwater protozoa
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Green Algae
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Unicellular w/two
flagella
Unicellular,
colonial
Multicellular
Unicellular, multinucleate,
filamentous
Green Algae
Is Volvox a colonial
species or a
multicellular
organism?
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