Objective: Chapter 28- Protists

Overview: Living Small

• Even a low-power microscope can reveal a great variety of organisms in a drop of pond water

• Protist is the informal name of the kingdom of mostly unicellular eukaryotes

• Advances in eukaryotic systematics have caused the classification of protists to change significantly

• Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom

What’s in a junk drawer?

Kingdom Protista is very diverse and where scientists place eukaryotes that are not animals, plants, or fungus.

Basic Characteristics of Protists

• Have eukaryotic cells (has a nucleus and organelles)

• Most are unicellular, algae is multicellular

• Very diverse kingdom

Protist Complexity• Protists are unicellular, so thought to be

simple, but…

• The protist’s one cell must carry out many processes (consume food, excrete waste, reproduce, respond to stimuli), so considered to be the most complex of eukaryotic cells

Protists are grouped by how they get nutrition

1. Animal-like protists (protozoans) are heterotrophs that ingest food

2. Fungus-like protists are heterotrophs that feed on decaying organic matter

3. Plant-like protists (algae) are autotrophs that make their own food like plants

• 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

Endosymbiosis in Eukaryotic Evolution

• There is now considerable evidence that much protist diversity has its origins in endosymbiosis

• Mitochondria evolved by endosymbiosis of an aerobic prokaryote

• Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

Fig. 28-02-2

Cyanobacterium

Heterotrophiceukaryote

Over the courseof evolution,this membranewas lost.

Red alga

Green alga

Primaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Plastid

Dinoflagellates

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

• The plastid-bearing lineage of protists evolved into red algae and green algae

• On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote

Fig. 28-03a

Gr een

algae

Am

oeb

ozo

ans

Op

istho

kon

tsA

lveolates

Stram

eno

piles

Diplomonads

Parabasalids

Euglenozoans

Dinoflagellates

Apicomplexans

Ciliates

Diatoms

Golden algae

Brown algae

OomycetesE

xcavataC

hro

malveo

lataR

hizaria

Chlorarachniophytes

Forams

Radiolarians

Arch

aeplastid

a

Red algae

Chlorophytes

Charophyceans

Land plants

Un

ikon

ta

Slime molds

Gymnamoebas

Entamoebas

Nucleariids

Fungi

Choanoflagellates

Animals

Fig. 28-03h

50 µm

Fig. 28-03i20 µm

Fig. 28-03j

20 µm50 µm

Fig. 28-03l

100 µm

Protozoans (Protozoa = “little animal”)

1. Heterotrophs

2. Can move like most animals• Different because they are unicellular

• Animal-like protists, resemble animals in 2 ways

1. Protozoans With FlagellaZooflagellates:

• Move by flagella• Reproduce asexually by binary fission• Free-living in water, some are parasites

Specific Zooflagelletes 1. Trichonympha: live in the gut of termites,

enzymes digest cellulose in wood

2. Trypanosoma: a parasitic zooflagellate causes African Sleeping sickness spread by tsetse fly

3. Giardia: a parasitic zooflagellate, lives in intestines, found in contaminated drinking water

2. Protozoans With Pseudopodia

Protozoans that move by extending lobes of cytoplasm

PseudopodPseudopod:

• Extensions of cytoplasm • Pseudopod = “false foot”

http://www.youtube.com/watch?v=7pR7TNzJ_pA

• Ex: Amoeba

3. Protozoans With CiliaCiliates:

• Found free-living in freshwater envts.

• Short hair-like projections called cilia to move and feed

3. Protozoans With CiliaParamecium :

• A ciliate with many rows of cilia for movement

http://www.youtube.com/watch?v=fmwN_mD7TvY

Paramecium

3. Protozoans With Cilia

Some ciliates have just clusters of cilia in tufts like Stentor who uses its cilia “tuft” to capture food

http://www.youtube.com/watch?v=pds8w7C9FEw

4. Protozoans Lacking Motility (Apicomplexans)

• Spore-forming parasites (Sporozoans)• No structure for movement• Spore = reproductive cell

4. Protozoans Lacking Motility (Apicomplexans)

Plasmodium• The organism that causes malaria in humans,

spread by infected mosquitoes http://www.youtube.com/watch?v=JwsoK8O0lXE&list=PL0BFC02A301F673F3&index=3&feature=plpp_video

http://www.youtube.com/watch?v=RxZ7pdKqwZw&feature=bf_next&list=PL0BFC02A301F673F3&lf=plpp_videohttp://www.youtube.com/watch?

v=4aVUrGO97Zg&feature=bf_next&list=PL0BFC02A301F673F3&lf=plpp_video

http://www.youtube.com/watch?v=DPv0VstforY\

• Two flagella make them spin as they move through the water

• Dinoflagellate blooms are the cause of toxic “red tides”

Zooxanthellae

-A dinoflagellate

-Photosynthetic algae, mutalistic with reef-building coral

-Provide oxygen to coral

Fig. 28-10-1

0.5 µm

Inside human

Liver

Liver cell

Merozoite(n)

Red bloodcells

Gametocytes(n)

Haploid (n)

Diploid (2n)

Key

Merozoite

Apex

Red bloodcell

Fig. 28-10-2

0.5 µm

Inside human

Liver

Liver cell

Merozoite(n)

Red bloodcells

Gametocytes(n)

Haploid (n)

Diploid (2n)

Key

Merozoite

Apex

Red bloodcell

Zygote(2n)

FERTILIZATION

Gametes

Inside mosquito

Fig. 28-10-3

0.5 µm

Inside human

Liver

Liver cell

Merozoite(n)

Red bloodcells

Gametocytes(n)

Haploid (n)

Diploid (2n)

Key

Merozoite

Apex

Red bloodcell

Zygote(2n)

FERTILIZATION

Gametes

Inside mosquito

MEIOSIS

Oocyst

Sporozoites(n)

Fungus-like protists:• Live in damp environments and help break down

organic matter (decomposers)

Plasmodial Slime Molds• Mass of cyoplasm, no individual cells

• Found on decomposing matter

http://www.youtube.com/watch?v=GScyw3ammmk

Cellular Slime Molds• Moves as a mass of independent cells

AlgaeAlgae: Plant-like protists that perform

photosynthesis and live in water

Unicelllar Algae (single-celled)Euglenoids (Euglena):

• Algae with a flagella

• Can do photosynthesis with light and w/out can be heterotrophs

Unicellular AlgaeDinoflagellates

• Algae with 2 flagella that spin the cells through water (salt water)

• Ex: fire algae causes red tides that produces a toxin

• Some are bioluminescent, glow when disturbed

Diatoms

• No cilia or flagella• Have glass like cell walls containing silica• Create Diatamaceous Earth

• Diatoms are a major component of phytoplankton and are highly diverse

• Fossilized diatom walls compose much of the sediments known as diatomaceous earth

Zooxanthellae

• Plant-like single celled algae in coral

• Provides coral (animal) with food and oxygen

• Coral provides habitat and CO2 for photosynthesis

Multicellular Algae (many cells)

Green Algae

• Grows in ponds, moist soil, fish tanks• Ancestor of modern plant

Brown Algae

• Most common seaweed• Include Giant Kelp, important habitat, area of

fish spawning

Red algae

• Found in warmer water• B/c of red pigment can photosynthesize at

deeper depths

Golden Algae

• Golden algae are named for their color, which results from their yellow and brown carotenoids

• All golden algae are photosynthetic, and some are also heterotrophic

• Most are unicellular, but some are colonial

• Giant seaweeds called kelps live in deep parts of the ocean

• The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus

• The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades

Fig. 28-15

Blade

Stipe

Holdfast

Alternation of Generations

• A variety of life cycles have evolved among the multicellular algae

• The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms

Fig. 28-16-1

10 cm

Haploid (n)Diploid (2n)

Key

Sporangia

Sporophyte(2n)

Zoospore

MEIOSIS

Female

Gametophytes(n)

EggMale

Sperm

Fig. 28-16-2

10 cm

Haploid (n)Diploid (2n)

Key

Sporangia

Sporophyte(2n)

Zoospore

MEIOSIS

Female

Gametophytes(n)

EggMale

Sperm

FERTILIZATION

Zygote(2n)

Developingsporophyte

Mature femalegemetophyte(n)

Fig. 28-UN6