Protists 1: Classification and Ecological Roles

Question 1

Whittaker’s Five Kingdom System included the Kingdom Protista

Answer 1

Defining characteristic: Eukaryotes that did not fit into the Plant, Animal, or
Fungus kingdoms

Question 2

Diversity
o Size and complexity

Answer 2

 Most protists are unicellular, although some are colonial or multicellular
 Examples
o Unicellular: Euglena
o Colonial: Dinobryon
o Multicellular: Kelp
 Single-celled protists are considered the simplest eukaryotes, but at the cellular
level, many are among the most complex and elaborate of all cells
 Include the same eukaryotic organelles we have discussed
 Include some unique organelles not found in most other eukaryotes

Question 3

Diversity
o Nutrition

Answer 3

 Some are photoautotrophs and have chloroplasts
 Some are heterotrophs, absorbing organic molecules or ingesting larger food
particles
 Others are mixotrophs, using both photosynthesis and heterotrophic nutrition

Question 4

Diversity
o Reproduction

Answer 4

 Some only reproduce asexually (binary fission)
 Some only reproduce sexually (gametes)
 Some have extremely complex life cycles that involve multiple forms of the
organism, some of which reproduce sexually and others asexually (Example:
Plasmodium sp. -> Malaria)

Question 5

Ecological roles
o Most protists are aquatic and are found almost anywhere there is water

Answer 5

 Oceans
 Fresh water
 Damp soil
 Wet leaf litter

Question 6

Ecological roles
o Some are producers

Answer 6

 Photosynthetic protists are THE main producers in aquatic communities
 Photosynthetic protists account for approximately 30% of the total
photosynthesis that takes place on earth
o Photosynthetic protists: 30%
o Land plants: 50%
o Photosynthetic prokaryotes (e.g. cyanobacteria): 20%
 Include
o Diatoms
o Dinoflagellates
o Algae

Question 7

Ecological roles
o Some are decomposers

Answer 7

Help to recycle organic and inorganic matter

Question 8

Ecological roles
o Some are symbionts

Answer 8

 Wood-digesting protists in the guts of termites and ruminants
 Coral reefs
 Photosynthetic dinoflagellates -> carbon
 Coral polyps (animals) -> structure

Question 9

Ecological roles
o Some are parasites

Answer 9

 Examples:
 Plasmodium sp. (Malaria)
 Trichomonas vaginalis (Trichomoniasis [STD])
 Giardia lamblia (Giardiasis [“Beaver Fever”])
 Trypanosoma brucei (African Sleeping Sickness)
 Chryptosporidium parvum (Cryptosporidiosis)
 Toxoplasma gondii (Toxoplasmosis)

Question 10

Eukaryotic Evolutionary History

Answer 10

o Our understanding of eukaryotic evolutionary history has been in flux in recent years
o There is much we don’t know about the evolutionary path of the eukaryotic groups in
existence today

Question 11

The current hypothesis places all eukaryotes into four major groups (“Supergroups”)

Answer 11

Exavata
“SAR Clade
Archaeplastida
Unkonta

Question 12

Excavata

Answer 12

 Diplomonads
 Parabasalids
 Euglenozoans

Question 13

“SAR’ clade

Answer 13

 Stramenopiles
o Diatoms
o Brown algae
 Alveolates
o Dinoflagellates
o Apicomplexans
o Ciliates
 Rhizarians
o Forams
o Cercozoans

Question 14

Archaeplastida

Answer 14

 Red algae
 Green algae
 Land plants

Question 15

Unkonta

Answer 15

 Amoebozoans
o Gymnamoebas
o Slime molds
 Opisthokonts
o Nucleariids
o Fungi
o Choanoflagellates
o Animals

Question 16

 Supergroups
o Excavata

Answer 16

 Excavata refers to a conspicuous feeding groove that appears to have been
“excavated” from one side
 Many lack “classical” mitochondria, but have modified mitochondria or
mitochondrial remnants that show they all originally had them

Question 17

Supergroups
o Excavata
[] Mitosomes

Answer 17

o Only recently discovered
o Remnants of mitochondria
o Same general structure
o No Krebs Cycle, No ETS
o Activity: maturation of Fe-S proteins

Question 18

Supergroups
o Excavata
[] Hydrogensomes

Answer 18

o Same general structure as mitochondria
o Function to produce ATP anaerobically
o Produce hydrogen gas as byproduct

Question 19

Supergroups
o Excavata
[] Kinetoplast-mitochondrion complex

Answer 19

o A single, oversized, mitochondrion contains a dense mass of
many copies of the mitochondrial genome (kinetoplast)
o The complex appears to function like normal mitochondria, just
has a unique structure

Question 20

Parabasalids
o Flagella

Answer 20

 Possess a cluster of flagella near the cell anterior
 One long flagellum is attached by an undulating
membrane that spans the length of the cell

Question 21

Parabasalids
o Named for a distinctive structure: parabasal body

Answer 21

 Associated with parabasal fibers
 Possibly a modified Golgi complex

Question 22

Parabasalids
o Anaerobic

Answer 22

 Lack true mitochondria
 Obtain ATP via hydrogenosomes

Question 23

Parabasalids
o Some form symbiotic relationships in animals

Answer 23

 Termites
 Cockroaches
 Ruminants

Question 24

Parabasalids
o Many are parasites

Answer 24

 Example: Trichomonas vaginalis
 Disease: Trichomoniasis (STD)
o Men: asymptomatic
o Women:
 More susceptible to 2o
infections
 Genital warts
 Cervical cancer
 Pre-term delivery

Question 25

Diplomonads o Flagella

Answer 25

 Possess multiple flagella, symmetrically located  Anterior flagella  Posterolateral flagella  Ventral flagella  Caudal flagella

Question 26

Diplomonads o Nuclei

Answer 26

Named for their two identical, symmetrically distributed, niclei

Question 27

Diplomonads o Lack some common organelles

Answer 27

 No lysosomes  No peroxisomes  No Golgi apparatus  No mitochondria

Question 28

Doplomonads o possess mitosomes (maturation for Fe-S proteins)

Answer 28

 Anaerobic  Fermentative metabolism o Sugars o Amino acids

Question 29

Doplomonads

Answer 29

o Most are commensal in the intestinal tracts of animals o A few are free living in stagnant water

Question 30

Doplomonads o Some are parasitic

Answer 30

 Example: Giardia lamblia  Disease: Giardiasis (“Beaver fever”) o Diarrhea, abdominal pain, weight loss o Spreads via cysts in fecal matter o Obtained by drinking untreated water

Question 31

Euglenozoans o Flagella

Answer 31

 Most have two parallel flagella extending from an apical pocket near the mouth  Each flagellum contains paraxonemal, rods

Question 32

Euglenozoans O two major types

Answer 32

 Euglena  Habitats: free-living (fresh & salt water)  Mitochondria: normal aerobic function  Autotrophic  Photosynthetic o Possess unique rod chloroplasts  Some are mixotrophic o Light: photosynthetic o Dark: Engulfs prey by phagocytosis  Kinetoplastids  Named for the presence of a single large mitochondrion containing the kinetoplast  Includes several parasites o Example: Trypanosoma brucei  Transmission: insect bite  Disease: African Sleeping Sickness  Stage 1: Fever, headache, joint pain  Stage 2: Breaches blood/brain barrier Changes in behavior, Coordination problems, Changes in sleep patterns

Question 33

Stramenopiles  Possess two dissimilar flagella

Answer 33

 Hairy flagellum  Smooth (hairless) flagellum

Question 34

Stramenopiles [] Named for the hairy flagellum

Answer 34

 Stramen- =straw (referring to flagellum)  -pile = hair

Question 35

Stramenopiles o Three major groups

Answer 35

Diatoms Golden algae Brown algae

Question 36

Diatoms

Answer 36

o Key group of photosynthetic protists o Unicellular o Silicon dioxide cell wall (frustule) o Diverse group > 100,000 living species o Among the most abundant phototrophs in oceans and lakes o Responsible for sediments known as diatomaceous earth  Used for:  Filtration (water filters, swimming pools)  Abrasives  Toothpaste  Skin exfoliators  Metal polishes  Pest control  Anticaking agents (food ingredients) o So widespread and abundant that blooms affect global CO2 levels  Use high amounts of CO2 to replicate  Upon death, sink to ocean floor, tying up organic carbon for centuries  Some scientists advocate promoting diatom blooms as a means of reducing atmospheric CO2 levels

Question 37

Golden algae

Answer 37

o Characteristic color results from yellow and brown carotenoids o All species are photosynthetic o Some species are mixotrophic o Most species are unicellular o Some species are colonial

Question 38

Brown algae

Answer 38

o The largest and most complex of the algae o Characteristic color results from brown carotenoids in their plastids o All are multicellular and photosynthetic o Most are marine (Seaweeds & Kelps)

Question 39

Alveolates o Characterized by the possession of membrane-enclosed sacs (alveoli) just under the plasma membrane

Answer 39

 Filled with fluids  Function: unknown o Temperature regulation o Strength (thick “skin”)

Question 40

Alveolates o Groups

Answer 40

Dinoflagellates Apicomplexans Ciliates Rhizarians Unikonts

Question 41

Alveolates o Groups - Dinoflagellates

Answer 41

o Cells are reinforced by cellulose plates o Possess a spiral flagellum that lines within a groove between the plates o Causes cells to spin as they move o Mainly marine, some freshwater species o Diverse nutrition  Some are photosynthetic  About half are strictly heterotrophic  Have plastids  Indicative of phototrophic ancestors  Many are mixotrophic o Responsible for “Red Tide” algal blooms  Cause massive fish kills  Toxins  Oxygen depletion o Many produce bioluminescence  Use luciferase and luciferin (substrate)  Emit a blue-green light  Light stimulated by disturbance  May be a defensive strategy  May startle potential predators  May attract higher order predators

Question 42

Alveolates o Groups - Apicomplexans

Answer 42

o Named for a complex at the cell apex that is specialized for penetrating host cells and tissues o Possess a unique organelle: Apicoplast  Contains its own DNA  Appears to be a vestigial chloroplast  Non-photosynthetic  Shows relationship to phototrophs  Role:  Lipid biosynthesis  Iron metabolism o Nearly all are parasites of animals  Have intricate life cycles with both sexual and asexual stages  Often require two or more host species  Many are transmitted via insect bite  Live mainly inside cells, hidden from the host’s immune system  Exhibit antigenic variability  Examples:  Plasmodium sp.  Malaria o Transmitted by mosquitoes o Resides in liver & RBC o Fever, chills, flu-like symptoms  Cryptosporidium parvum  Cryptosporidiosis o Passed via contaminated water o Explosive diarrhea, low fever, abdominal pain  Toxoplasma gondii  Toxoplasmosis o Passed via contaminated, undercooked meat, water, or direct contact with fecal matter (e.g. cat litter box), mother-fetus o Flu-like symptoms, brain damage, behavior modifications, eye damage o 60 million in US infected

Question 43

Alveolates o Groups - Ciliates

Answer 43

o Named for use of cilia to move and feed  Cilia of some completely cover cell  Cilia of some are clustered in rows/tufts o Most are predators  Prey  Bacteria  Small protists  Food moved to oral grove by oral cilia  Enters cell mouth  Moves to gullet  food vacuoles  Digestion o Distinctive feature: two types of nuclei  Generative nucleus (Micronucleus)  Diploid, carries cell germline  Passed from parent to offspring  Genes are not expressed  Vegetative nucleus (Macronucleus)  Polyploid  Expresses the phenotype of the cell  Generated from micronucleus  Amplification & editing o 10  20,000 chromosomes o Most contain a single gene o Reproduction  Asexual  Transverse fission, budding, others  Sexual: Conjugation  Two cells form a cytoplasmic bridge  Macronuclei dissemble  Micronuclei undergo meiosis  Haploid micronuclei exchange  Cells separate, new macronuclei form

Question 44

Alveolates o Groups - Rhizarians

Answer 44

 Amoebas with needle-like pseudopodia  Use these to move and feed  Three sub-groups  Radiolarians o Intricate internal skeletons of silica o Pseudopodia radiate outward o All live in marine environments o Free floating (planktonic)  Foraminiferans (Formas) o Have porous shells of CaCO3  Most are less than 1 mm in size, but some are much larger, up to 20 cm long  Pseudopodia extend through the pores for swimming and feeding o Live in both marine and freshwater  Generally live in sand or attach themselves to rocks or algae  Some are abundant in plankton  Cercozoans o Common inhabitants of marine, freshwater, and soil ecosystems o Most are heterotrophs o Many are predators  Bacteria  Small protists  Fungi o Some enslave photosynthetic prey o Some are parasites of plants, animals, or other protists o Essentially: Similar to Radiolarians and Foraminiferans except that they have no internal skeleton or shell

Question 45

Alveolates o Groups - Archaeoplastida

Answer 45

o Generally referred to as Plantae sensu lato o (“Plants in the broad sense”) o It is the clade that includes:  Land plants  Green Algae  Red Algae o Common features:  All have photosynthetic chloroplasts  Most have cell walls of cellulose o Major divisions  Glaucophyta  small freshwater single-celled algae  Chloroplasts have peptidoglycan layer  Rhodophyceae  Red algae  Most are marine seaweeds  Multicellular  Red color comes from phycobiliproteins: accessory pigments used in light capture for photosynthesis  Chloroplastida  Land plants and many green algae  All have chloroplasts without peptidoglycan or phycobiliproteins

Question 46

Alveolates o Groups - Unikonts [] Amoebozoans

Answer 46

 Amoeba with lobe- or tube-shaped pseudopodia  Subgroup 1: Slime molds o Feed on microorganisms that live on dead plant material: forest floors, logs, lawns o Often brightly colored yellows and oranges o Once thought to be fungi: produce fruiting bodies for spore dispersal  DNA sequence analyses indicate that the resemblance between slime molds and fungi is a case of evolutionary convergence  Subgroup 2: Tubulinids o (Example: Amoeba proteus) o Unicellular amoeba o Ubiquitous in soil, freshwater and marine environments o Most are heterotrophs that actively seek and consume bacteria and other protists  Subgroup 3: Entamoebas o All are parasites o Infect vertebrates and some invertebrates o (Example: Entamoeba histolytica) o Spread via contaminated food and water o Typically eats bacteria and food particles o Can start attacking epithelial cells  necrosis o Enters bloodstream and damages other organs o Responsible for 100,000 deaths annually

Question 47

Alveolates o Groups - Unikonts [] Opisthokonts

Answer 47

 Nucleariids (fungus-like protists)  Small spherical amoeba with thread-like pseudopodia  Similar appearance to Rhizarians  DNA sequencing shows they are more closely-related to fungi  Thrive in soils and freshwater  Heterotrophic o Prey on—  Algae  Cyanobacteria  Choanoflagellates (animal-like protists)  Choanos (Gk) = funnel  Free-living unicellular and colonial flagellate eukaryotes  Ovoid cells with collar of microvilli  Closely related to animals  Similar appearance to choanocytes (collar cells of sponges), suggesting a strong evolutionary relationship  Movement of the flagellum creates water currents o Trap bacteria and detritus against the collar  phagocytosis  Colonial types create extracellular matrix  lorica (basket-shaped houses)