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Algae. Algae (singular: alga) are photosynthetic protists, usually aquatic - not a phylogenetically meaningful term, but widely used - despite their complexity, algae are NOT PLANTS Algae are responsible for most photosynthesis in the ocean

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Algae (singular: alga) are photosynthetic protists, usually aquatic

- not a phylogenetically meaningful term, but widely used

- despite their complexity, algaeare NOT PLANTS

Algae are responsible for most photosynthesis in the ocean

(which covers 70% of the planet’s surface)

Shallow water dominated by macroalgae with large, multicellular

bodies; critical as food for near-shore animals

- giant kelp Macrocystis pyrifera, sea lettuce Ulva lactuca

Open ocean dominated by phytoplankton: single-celled

photosynthesizers that fix CO2

- form the basis of the food web; they are eaten by little critters,

which are eaten by fish, which are eaten by bigger fish...

gametic life cycle
Gametic life cycle

No gametophyte (haploid body) -- Gametes are only haploid cells

sperm +



Sporic life cycle

common among multicellular protists like algae; one stage built

out of haploid cells, another made of diploid cells

alternation of generations haploid diploid stages may look different
Alternation of Generations:haploid & diploid stages may look different

meiosis only occurs in the

sporophyte stage

alternation of generations
Alternation of Generations

Many protists exhibit alternation of generations, in which a

multicellular haploid stage alternates w/ multicellular diploid stage

1)Meiosis produces spores(N, haploid), which grow into a whole

haploid body called the gametophyte

2) The gametophyte produces gametes (sperm + eggs) by mitosis

3) Syngamy produces the zygote, “the baby” (2N, diploid)

4) The zygote grows into the sporophyte stage (2N, diploid),

which undergoes meiosis...

phylum chlorophyta green algae
Phylum Chlorophyta: Green Algae

Chloroplasts very similar to those in true plants

- chlorophyll a and b

Green algae share a common ancestor with land plants, and are

included in the “Kingdom Plantae” by some

Some Chlorophytes live symbiotically with fungi as lichens,

super-organisms that grow on rocks in moist terrestrial


phylum rhodophyta red algae
Phylum Rhodophyta: Red Algae

Red from an accessory pigment, phycoerythrin

- allows absorption of blue + green light, the wavelengths that

penetrate the deepest in ocean water (red is reflected)

Some have lost their plastids,

become parasites on other algae

- may explain why endosymbiosis

occurred repeatedly in this group

Nori, used in sushi rolls,

is the red alga Porphyra

phylum stramenopiles brown algae
Phylum Stramenopiles - Brown algae

Largest, most complex multicellular colonies of any protist

- convergent evolution has resulted in many plant-like features

- blades look like leaves; stipes look like stems;

holdfasts look like roots

However, brown algae lack truetissues which exist in land plants





phylum stramenopiles brown algae10
Phylum Stramenopiles - Brown algae

Giant kelp Macrocystis can grow 1 meter per day, 60 m in a year!

- fastest growth rate of any organism on the planet

Grows here in CA because

coastal upwelling brings nutrient-

rich bottom water to the surface

- supports a diverse community of

fish + other animals that depend

on the kelp to support the food web

phylum stramenopiles brown algae11
Phylum Stramenopiles - Brown algae

Diploid (2N)


Haploid (1N)



(male + female)

diatoms phylum stramenopiles
Diatoms (Phylum Stramenopiles)

Diatoms contribute half of the primary production in marine ecosystems

- secrete 2-valve shell of silicate (glass) over plasma membrane

phylum dinoflagellata
Phylum Dinoflagellata

Possess 2 flagella that twirl as they swim (Greek dinos, whirling)

Can be autotrophic (photosynthetic), heterotrophic, or some

can even switch back and forth (mixotrophic)

Include the photosynthetic endosymbionts of hard corals

phylum dinoflagellata15
Phylum Dinoflagellata

Can cause red tides, up to 100 million cells per liter

- use up all O2, leading to

mass kills of sea life

- locally, create intense

bioluminescence in

breaking waves at night

phylum dinoflagellata16
Phylum Dinoflagellata

Include photosynthetic endosymbionts of hard corals

Can cause red tides, up to 100 million cells per liter

- increasing in frequency, due to run-off from agriculture

- produce potent toxins, which concentrate in filter feeders

(clams, mussels) and are very dangerous to humans:

- saxitoxins: Paralytic Shellfish Poisoning

- other toxins: Diarrhetic or Amnesiac poisoning


Economic development can occur at the expense of

environmental quality

Increasing incidence

of red tides in Chinese

seas …

…coincident with

increased economic

Development (GDP)

Liu & Diamond (2005)

Nature 435:1179-1186

animal like protists
Animal-like protists

Diverse heterotrophic lineages of eukaryotes

Alveolates -- ciliates, Plasmodium (malaria parasite)

Euglenids -- Euglena, Trypanosoma (sleeping sickness parasite)

Amoebazoans -- Amoeba

Diplomonads -- Giardia

alveolata 3 related phyla
Alveolata: 3 related phyla

Phylum Dinoflagellata – dinoflagellates

Phylum Ciliophora– ciliates

Phylum Apicomplexa– includes malaria parasite

Note the diversity of metabolic processes and lifestyles found

in this one group of protists –

- parasites & endosymbionts

- free-living heterotrophs

- autotrophs & mixotrophs

phylum ciliophora paramecium
Phylum Ciliophora– Paramecium

Bacteria are pushed along

food groove into mouth

by cilia

Food is engulfed

by phagocytosis,

digested in food


phylum ciliophora
Phylum Ciliophora

Ciliated protozoans, eg. Paramecium

- tiny hairs called cilia beat together, making water flow

past the body propels cell forward

phylum apicomplexa
Phylum Apicomplexa

Plasmodium causes malaria, affects 500 million people and

kills 2 million per year

Spread by female Anopheles mosquito;

can only complete its life cycle when

syngamy happens inside a mosquito

- stays inside our liver + blood cells;

hard for our immune system to attack it

- eats hemoglobin

- contain a non-functioning plastid,

formerly a green alga endosymbiont

phylum kinetoplastida
Phylum Kinetoplastida

Trypanosomes – parasitic

- have both an insect and a vertebrate host

- Trypanosoma causes African Sleeping Sickness (tsetse fly)

- other species cause leishmaniasis, Chagas’ disease

(infect >20 million in Central and South America)

Evade host immune response by constantly changing proteins

that coat their cell surface, which would otherwise be recognized

by antibodies produced by our immune system

- rotate among 1,000 genes for surface proteins

Single, elongated mitochondrion with entwined circles of DNA

called the kinetoplast

phylum euglenida
Phylum Euglenida

Some are photosynthetic

- like plants, plastid was formerly a cyanobacterium

Move using a whiplike flagellum

May only be asexual (very rare)


Named for pseudopods, temporary extensions of cytoplasm used in

feeding and locomotion

Look for action of water

vacuoles -- organelles that

collect water as it flows into

the cell, then expel it so the

cell doesn’t pop

Phagocytosis: food particles are

engulfed in vesicles, followed by

intracellular digestion


Related to amoebae, but with a shell of

calcium carbonate covering

plasma membrane

Pseudopods extrude through holes in test, trap prey

- empty shells contribute to carbonate depositions on sea floor

(chalk layers, great pyramid building blocks)






Isotopecomposition of calcium carbonate shells = a record

of past temperatures, critical for studies of past climate change


Includes Giardia, the worst most

awful parasite in the world

(because it came after me)

Weird cells: 2 nuclei, 8 flagella

- lack mitochondria, Golgi, smooth Endoplasmic Reticulum

 once thought to be a transitional stage between prokaryotes

and eukaryotes

 actually just very simplified cells that lost most features,

which they no longer need because of their parasitic lifestyle