8- Taxonomy of Eukaryotes

Question 1

What is the Phylogeny of the Eukarya?

Answer 1

• Sequencing of 18S rRNA genes is used to infer the phylogeny of eukaryotes.
• relationship between 18S rRNA genes is weaker for eukaryotes than 16S rRNA genes is for prokaryotes.

• Phylogenies have been constructed by taking into account other genes (e.g.,
tubulin, RNA polymerase, and ATPase) – MLST.

• New insights have arisen because of these new phylogenies (e.g., fungi and
animals are closely related and they are close to the amoebozoa).

• Eukaryotic molecular phylogeny is still being refined.

Question 2

What are the 6 phylogeny of the Eukarya?

Answer 2

Archaeplastida, rhizaria, chromalveolata, excavata, amoebozoa, opisthokonta

Question 3

Characteristic of red algae?

Answer 3

Red algae are also called
rhodophytes
• Mostly marine, but some
freshwater and terrestrial
• Red color is from phycoerythrin, an accessory pigment. At greater depth, more phycoerythrin is produced by cells.
• Most species are mulFcellular.
• Unicellular: Galdieria, lives in
acidic hot springs.

Question 4

Characteristic of green algae?

Answer 4

Green algae are also called
chlorophytes
• Closely related to plants
• Most green algae inhabit freshwater, but some are marine or terrestrial
• Can be unicellular (usually flagellated) to multicellular.
• Have sexual and asexual reproduction.
• Endolithic algae grow inside porous rocks

Question 5

What are endosymbiosis?

Answer 5

symbiosis in which one of the symbiotic organisms lives inside the other.

Question 6

What are Amitochondriate eukaryotes? Mitosome? Hydrogenosome?

Answer 6

Eukaryotes that lack a mitochondrion. At first, they looked like very primitive
eukaryotes.

• Instead, they have:
– Mitosome: reduced form of
mitochondrion – derived from
mitochondrion – that does not have enzymes of the TCA cycle and does not have a respiratory chain. They are involved in the maturation of iron-sulfur
clusters.

– Hydrogenosome: present in eukaryotes whose metabolism is strictly fermentative. It carries out the oxidation of pyruvate to H2, CO2 and acetate. Sometimes H2-consuming endosymbiotic bacteria are also present (methanogens)
– secondary endosymbiosis.

Question 7

What is a cyst?

Answer 7

Some species of protists are able to differentiate into cysts, becoming encysted.

• Cysts are similar to the endospores produced by prokaryotes.
• Protect the cells against deleterious environmental conditions.
• Survive long periods of starvation and/or desiccation.
• Survive infection by prokaryotes.

Question 8

What are diplomonads? Parabasalids?

Answer 8

• Unicellular
• Flagellated
• Lacks chloroplasts
• Live in anoxic habitats

• Diplomonads
– Have two nuclei of equal size
– Have mitosomes (degenerated mitochondria)
– Key genera: Giardia (cause giardiasis)

• Parabasalids
– Contain a parabasal body (structural support to the golgi complex)
– Lack mitochondria, but have hydrogenosomes for anaerobic metabolism
– Live in the intesFnal and urogenital tracts of animals as parasites or
symbionts.
– Key Genera: Trichomonas
like Giadia lamblia

Question 9

What is Trichomonas vaginalis?

Answer 9

Parabasalids
• STD in humans: most common parasitic infection in developed countries.
• Does not form cysts, does not survive well outside the host (adapted to sexual
transmission).

Question 10

What are euglenozoans?

Answer 10

Euglenozoans: unicellular
flagellated eukaryotes

• Kinetoplastids
– Named for the presence of the kinetoplast, a mass of DNA present in their single, large mitochondrion
– Live primarily in aquatic habitats feeding on bacteria
– Some species cause serious diseases in humans

Question 11

What is Trypanosoma brucei?

Answer 11

Causes African sleeping sickness, a chronic and usually fatal infection.
• Lives and grows in the bloodstream, infects the central nervous system during the later stage.
• Transmieed by the tsetse fly.
• The single flagellum is enclosed in a membrane flap.

Question 12

What are euglenids?

Answer 12

• Euglenids
– Nonpathogenic and phototrophic.
– Contain chloroplasts, can exist as heterotrophs; will lose its chloroplast if incubated in
the dark for a long Fme.
– Can feed on bacteria by phagocytosis.

Question 13

What is alveolates?

Answer 13

Alveolates are characterized
by the presence of alveoli,
which are sacs underneath
the cytoplasmic membrane
– May function to help cells
maintain osmotic balance
– In Paramecium:
contractile vacuole.
• Members are ciliates,
dinoflagellates, and
apicomplexans

Question 14

What are ciliates?

Answer 14

Alveolate
• Possess cilia at some stage of their life
• Most widely distributed genera is Paramecium à
• Use cilia for motility and to obtain food
• Ciliates have two nuclei (macronucleus and micronucleus)
• During conjugation – sexual
reproduction – two paramecia
exchange micronuclei
• Some ciliates are animal parasites, some are animal symbionts (in the rumen).

Question 15

What is dinoflagellates?

Answer 15

Alveloate
Diverse marine and freshwater
phototrophic organisms
• Some are free-living and others live symbiotically with corals
• Have two flagella with different insertion points on the cell
– Transverse flagellum
– Longitudinal flagellum

Question 16

Toxicity of dinoflagellates

Answer 16

Some species secrete neurotoxins.
• In warm and polluted waters,
dinoflagellates can reach very high numbers.
• Dense suspensions of these cells are called red tides
• Associated with human poisoning (paralytic shellfish poisoning). Accumulation of toxic dinoflagllates in mussels.

Question 17

What are apicomplexans?

Answer 17

Alveolate
Obligate parasites of animals
• Complex life cycle:
– Sporozoite (transmission)
– Gametocyte (sexual reproduction)
– Other stages

• Contain apicoplasts, degenerate chloroplasts that lack pigments and phototrophic capacity, but still carry many anabolic pathways.
• Cause severe diseases such as malaria (Plasmodium), toxoplasmosis (Toxoplasma), and coccidiosis (Eimeria).

Question 18

What are stramenopiles?

Answer 18

All have flagella with many short hairlike extensions
• Chemoheterotrophs and phototrophic members
• Oomycetes, diatoms, golden algae, and brown algae

• Oomycetes (chemoheterotrophs)
– Also called water molds based on their filamentous growth and the presence of coenocytic
hyphae (multinucleate)
– Cell walls are made of cellulose, not chitin as in fungi
– Phytophthora infestans causes the late blight disease in potatoes and contributed to the Irish potato famine

• Golden algae (phototrophs)
– Also called chrysophytes
– Most are unicellular, some are colonial
– Golden algae are named for their golden-brown color
– Chloroplast pigments dominated by the carotenoid fucoxanthin

Question 19

What are diatoms? Frustule?

Answer 19

Unicellular, phototrophic.
• Over 100,000 species of diatoms
• Freshwater and marine habitats

• Frustules: cell walls made of silica with proteins and polysaccharides aeached to it. Protect against predation.
• Appeared on Earth about 200 million years ago

Question 20

What are Cercozoans and Radiolarians? Foraminifera? Radiolarians?

Answer 20

Distinguished from other protists by their
threadlike pseudopodia

• Cercozoans: Foraminifera:
– Exclusively marine organisms
– They form shell-like structures called tests
– Tests are made from organic materials reinforced
with calcium carbonate

• Radiolarians
– Mostly marine, heterotrophic organisms
– Tests are made of silica
– Name is derived from radial symmetry of tests

Question 21

What is Amoebozoa? gymnamoebas, entamoebas, and slime molds?

Answer 21

Terrestrial and aquatic protists that use pseudopodia for movement and feeding (phagocytosis of bacteria and
smaller protists). Move by amoeboid movement (cytoplasmic streaming)

• Major groups are gymnamoebas, entamoebas, and slime molds

• Gymnamoebas
– Free-living, inhabit soil and aquatic environments

• Entamoebas
– Parasites of vertebrates and invertebrates
(Ex: Entamoeba histolytica)

Slime mold: Previously grouped with fungi because they have similar life cycle: produce fruiting bodies with spore for dispersal.
• Motile, can move across surfaces rapidly

Question 22

What is Plasmodial slime molds

Life cycle?

Answer 22

Have vegetative forms that
are masses of protoplasm of
indefinite size and shape
(plasmodium), that contain
multiple nuclei.

• From the plasmodium, a
sporangium can form,
containing multiple haploid
spores (dormant, resistant, for
dispersal).

• The spores germinate, yielding
a swarmer cell (flagellated or
amoeboid). The fusion of two
swarmer cells regenerates the
diploid plasmodium.

Question 23

What is Amoebozoa – cellular slime mold?

Answer 23

• Cellular slime molds: vegetative forms composed of single amoebae (haploid).
• Aggregate as a pseudoplasmodium (slug) that can move as a single unit (cells do not fuse).
• Fruiting body is formed, cells differentiate into spores.
• May form diploid macrocysts (diploid) that undergo meiosis to form new amoebae (haploid): sexual reproduction.

Question 24

What are fungi?

Answer 24

• Most fungi are multicellular, forming a network of hyphae (mycelium).
– Coenocytic: cytoplasm and nuclei are not subdivided into cells.
– Septate: nuclei are separated by cross wall.

• Hyphae that extend above the surface can produce asexual spores called conidia.
Conidia are oren pigmented and resistant to drying.

• Most fungal cell walls are made of chitin.
• Feed by secreting extracellular enzymes that digest complex organic materials (polymers). Monomers, or short polymers are then assimilated.

Question 25

What are symbioses and pathogenesis? Ectomyco, endo?

Answer 25

• Symbiotic association:
– Some species of fungi form close relationships with plant roots (mycorrhizae). Glomeromycetes
– Mycorrhizae help plant roots obtain phosphorus
– The fungi obtain nutrients from the plant.

• Ectomycorrhizae: form a sheath around the plant root but does not penetrate it.
• Endomycorrhizae: the fungal hyphae is embedded in the plant root.

Question 26

What are symbioses and pathogenesis? Mycoses?

Answer 26

Fungi can cause disease in plants and animals.
• Many fungal plant pathogens form specialized hyphae – haustoria – to penetrate the plant cells and consume the cytoplasm.

• Mycoses in humans range in severity from “athlete’s foot” to
histoplasmosis. Immunosuppression is a major risk factor.

Question 27

Explain fungal reproduction?

Answer 27

• Most fungi reproduce by asexual means (three forms)

1. Growth and spread of hyphal filaments
2. Asexual production of spores
3. Simple cell division (budding yeast)

• Some fungi produce spores as a result of sexual reproduction
– Sexual spores can originate from the fusion of two haploid cells to form a diploid cell that then, undergo meiosis to
produce haploid spores (ascospores, basidiospores, zygospores)
– Spores are resistant to drying, heating, freezing, chemicals

Question 28

What are Saccharomyces cerevisiae? Sexual reproduction?

Answer 28

• Cells are spherical to oval, cell division through budding.
• Sexual reproduction: mating types in Saccharomyces cerevisiae.