• 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

Euglenozoans have flagella with a unique internal structure

• Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

• Their main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella

Flagella

0.2 µm

Crystalline rod

Ring of microtubules

Kinetoplastids

• Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast

• They include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems

• The parasitic kinetoplastid Trypanosoma causes sleeping sickness in humans

9 µm

Euglenids

• Euglenids have one or two flagella that emerge from a pocket at one end of the cell

• The glucose polymer paramylon is also characteristic of this clade

5 µmEuglena (LM)

Plasma membrane

Nucleus

Short flagellum

Eyespot

Light detector

Contractile vacuole

Chloroplast

Paramylon granulePellicle

Long flagellum

Dinoflagellates

• Dinoflagellates are a diverse group of aquatic photoautotrophs and heterotrophs

• They are abundant components of both marine and freshwater phytoplankton

• Each has a characteristic shape that in many species is reinforced by internal plates of cellulose

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

• Rapid growth of some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans

3 µ

m

Flagella

Apicomplexans

• Apicomplexans are parasites of animals and some cause serious human diseases

• One end, the apex, contains a complex of organelles specialized for penetrating a host

• They have a nonphotosynthetic plastid, the apicoplast

• Most have sexual and asexual stages that require two or more different host species for completion

Sporozoites(n)

Inside mosquito

Oocyst

Zygote(2n)

MEIOSISMerozoite(n)

Livercell

Liver

FERTILIZATION

Gametes

Gametocytes(n)

Red bloodcells

Inside human

Merozoite

Apex

Red bloodcell

0.5 µm

Haploid (n)

Key

Diploid (2n)

Ciliates

• Ciliates, a large varied group of protists, are named for their use of cilia to move and feed

• They have large macronuclei and small micronuclei

• The micronuclei function during conjugation, a sexual process that produces genetic variation

• Conjugation is separate from reproduction, which generally occurs by binary fission

FEEDING, WASTE REMOVAL, AND WATER BALANCE

CONJUGATION AND REPRODUCTION

MEIOSIS

MICRONUCLEARFUSION

Haploidmicronucleus

Diploidmicronucleus

Diploidmicronucleus

Contractilevacuole

Oral groove

Cell mouth

Micronucleus

Macronucleus

50 µm

Thousands of cilia cover thesurface of Paramecium.

Paramecium, like other freshwater protists, constantly takes in water

by osmosis from the hypotonic environment. Bladderlike

contractile vacuoles accumulate excess water from radial canals

and periodically expel it through the plasma membrane.

Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis.

Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell.

The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.

Compatiblemates

Two cells of compatible mating strains align side by side and partially fuse.

Macronucleus

Meiosis of micronuclei produces four haploid micronuclei in each cell.

Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis.

The cells swap one micronucleus.

The cells separate.

Key Micronuclei fuse, forming a diploid micronucleus. Conjugation

Reproduction

Two rounds of cytokinesis partition one maccronucleus and one macronucleus into each of four daughter cells.

The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei.

Three rounds of mitosis without cytokinesis produce eight micronuclei.

Oomycetes (Water Molds and Their Relatives)

• Oomycetes include water molds, white rusts, and downy mildews

• They were once considered fungi based on morphological studies

• Most oomycetes are decomposers or parasites

• They have filaments (hyphae) that facilitate nutrient uptake

• Their ecological impact can be great, as in Phytophthora infestans causing potato blight

Egg nucleus (n)

MEIOSIS

FERTILIZATION

Haploid (n)

Key

Diploid (2n)

Oogonium

Antheridial hyphawith sperm nuclei (n)

SEXUALREPRODUCTION

Zygote germination Zygotes

(2n)Zoosporangium (2n)

Zoospore (2n)

Cyst

Germ tube

ASEXUALREPRODUCTION

Diatoms

• Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica

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

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

3 µ

m

50 µmDiatom diversity (LM)

Golden Algae

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

• The cells of golden algae are typically biflagellated, with both flagella near one end

• Most are unicellular, but some are colonial

25 µm

Brown Algae

• Brown algae, or phaeophytes, are the largest and most complex algae

• All are multicellular, and most are marine

• Brown algae include many species commonly called seaweeds

• Seaweeds have the most complex multicellular anatomy of all algae

• Giant seaweeds called kelps live in deep parts of the ocean (second slide)

Blade

Stipe

Holdfast

• Many seaweeds are important commodities

• Many are harvested for food

Human Uses of Seaweeds

The seaweed is grown on nets in shallow coastal waters.

A worker spreads the seaweed on bamboo screens to dry.

Paper-thin, glossy sheets of nori make a nutritious wrap for rice, seafood, and vegetables in sushi.

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

Developingsporophyte

Zygote(2n)

FERTILIZATIONMature femalegametophyte(n)

Egg

Sperm

MEIOSIS

Haploid (n)

Key

Diploid (2n)

Sporangia

Sporophyte(2n)

Zoospores

Female

Gametophytes(n)

Male

Cercozoans and radiolarians have threadlike pseudopodia

• A newly recognized clade, Cercozoa, contains species among the organisms called amoebas

• Amoebas were formerly defined as protists that move and feed by means of pseudopodia

• Cercozoans are distinguished from most other amoebas by their threadlike pseudopodia

Foraminiferans (Forams)

• Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests

• Pseudopodia extend through the pores in the test

• Foram tests in marine sediments form an extensive fossil record

20 µm

Radiolarians

• Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica

• Radiolarians phagocytose microorganisms with their pseudopodia

• The pseudopodia of radiolarians, known as axopodia, radiate from the central body

200 µm

Axopodia

Amoebozoans have lobe-shaped pseudopodia

• Amoebozoans are amoeba that have lobe-shaped, rather than threadlike, pseudopodia

• They include gymnamoebas, entamoebas, and slime molds

Gymnamoebas

• Gymnamoebas are common unicellular amoebozoans in soil as well as freshwater and marine environments

• Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists

Pseudopodia

40 µm

Entamoebas

• Entamoebas are parasites of vertebrates and some invertebrates

• Entamoeba histolytica causes amebic dysentery in humans

Slime Molds

• Slime molds, or mycetozoans, were once thought to be fungi

• Molecular systematics places slime molds in the clade Amoebozoa

Plasmodial Slime Molds

• Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange

• At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium

• The plasmodium is undivided by membranes and contains many diploid nuclei

• It extends pseudopodia through decomposing material, engulfing food by phagocytosis

4 cm

1 mm

MEIOSISHaploid (n)

Key

Diploid (2n)

Zygote (2n)

SYNGAMY

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Stalk

Amoeboid cells(n)

Germinatingspore

Flagellated cells(n)

Cellular Slime Molds

• Cellular slime molds form multicellular aggregates in which cells are separated by their membranes

• Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity

600 µm MEIOSIS

Haploid (n)

Key

Diploid (2n)

Zygote (2n)

SYNGAMY

Migratingaggregate

Emergingamoeba

SEXUALREPRODUCTION

Amoebas

Spores(n)

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodies

Aggregatedamoebas

200 µm

Red algae and green algae are the closest relatives of land plants

• Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont

• The photosynthetic descendants of this ancient protist evolved into red algae and green algae

Red Algae

• Red algae are reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll

• Red algae are usually multicellular; the largest are seaweeds

• Red algae are the most abundant large algae in coastal waters of the tropics

Bonnemaisonia hamifera, afilamentous red alga.

Dulse (Palmaria palmata). This edible species has a “leafy” form.

A coralline alga. The cells walls of corralline algae are hardened by calcium carbonate. Some coralline algae are members of the biological communities called coral reefs.

Green Algae

• Green algae are named for their grass-green chloroplasts

• Two main groups: chlorophytes and charophyceans

• They are closely related to land plants

• Most chlorophytes live in fresh water, although many are marine

• Other chlorophytes live in damp soil, as symbionts in lichens, or in snow

• Chlorophytes include unicellular, colonial, and multicellular forms

• Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages

Calperpa, an inter-tidal chlorophyte. The branched filaments lack cross-walls and thus are multinucleate. In effect, the thallus is one huge “supercell.”

50 µmVolox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM).

Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides.

20 µm

MEIOSIS

Haploid (n)

Key

Diploid (2n)

SYNGAMY

SEXUALREPRODUCTION

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

Zygote(2n)

Regionsof singlechloroplast

Nucleus

Flagella

Cell wall

1 µm

Animations and Videos

• Bozeman – Eukarya

• Bozeman – Protists

• Malaria: The Life Cycle

• Algae Life Cycle

• Chapter Quiz Questions – 1

• Chapter Quiz Questions – 2

If the mitochondria and chloroplasts in eukaryotic cells resulted from endosymbiosis, what features might we expect these organelles to contain?

• a plasma membrane, DNA, and ribosomes

• a plasma membrane, nucleus, and ribosomes

• nucleus, DNA, and ribosomes

• a plasma membrane, nucleus, and cilia

• nucleus, ribosomes, and cilia

If the mitochondria and chloroplasts in eukaryotic cells resulted from endosymbiosis, what features might we expect these organelles to contain?

• a plasma membrane, DNA, and ribosomes

• a plasma membrane, nucleus, and ribosomes

• nucleus, DNA, and ribosomes

• a plasma membrane, nucleus, and cilia

• nucleus, ribosomes, and cilia

Which of the following statements about slime molds is correct?

• Cellular slime molds have haploid zygotes.

• Cytoplasmic streaming helps distribute nutrients and oxygen in cellular slime molds.

• In plasmodial slime molds, the haploid condition is the dominant part of the life cycle.

• Cellular slime molds have fruiting bodies that function in sexual reproduction.

• Cellular slime molds form masses when food is scarce, but their cells remain separated.

Which of the following statements about slime molds is correct?

• Cellular slime molds have haploid zygotes.

• Cytoplasmic streaming helps distribute nutrients and oxygen in cellular slime molds.

• In plasmodial slime molds, the haploid condition is the dominant part of the life cycle.

• Cellular slime molds have fruiting bodies that function in sexual reproduction.

• Cellular slime molds form masses when food is scarce, but their cells remain separated.

The largest group of eukaryotic organisms is the

• vertebrates.

• animals.

• plants.

• protists.

• fungi.

The largest group of eukaryotic organisms is the

• vertebrates.

• animals.

• plants.

• protists.

• fungi.

Photosynthetic eukaryotes contain both mitochondria and chloroplasts. Which sequence most likely describes the evolution of this group?

• Ancestral anaerobic prokaryote engulfs heterotrophic prokaryote and then engulfs photosynthetic prokaryote.

• Ancestral anaerobic prokaryote engulfs photosynthetic prokaryote and then engulfs heterotrophic prokaryote.

• Both sequences are equally likely.

Photosynthetic eukaryotes contain both mitochondria and chloroplasts. Which sequence most likely describes the evolution of this group?

• Ancestral anaerobic prokaryote engulfs heterotrophic prokaryote and then engulfs photosynthetic prokaryote.

• Ancestral anaerobic prokaryote engulfs photosynthetic prokaryote and then engulfs heterotrophic prokaryote.

• Both sequences are equally likely.

Trypanosoma, a kinetoplastid, is the causative agent of

a) HIV/AIDS

b) Malaria

c) Giardiasis

d) Trichomoniasis

e) Sleeping sickness

Trypanosoma, a kinetoplastid, is the causative agent of

a) HIV/AIDS

b) Malaria

c) Giardiasis

d) Trichomoniasis

e) Sleeping sickness

Which of the following was not formed by secondary endosymbiosis?

a) Dinoflagellates

b) Stamenophiles

c) Euglenids

d) Clorarachniophytes

e) Cyanobacteria

Which of the following was not formed by secondary endosymbiosis?

a) Dinoflagellates

b) Stamenophiles

c) Euglenids

d) Clorarachniophytes

e) Cyanobacteria

Which of the following most likely arose from endosymbiosis?

• nuclear membrane and Golgi apparatus

• ER and chloroplasts

• chloroplasts and mitochondria

• mitochondria and Golgi apparatus

Which of the following most likely arose from endosymbiosis?

• nuclear membrane and Golgi apparatus

• ER and chloroplasts

• chloroplasts and mitochondria

• mitochondria and Golgi apparatus

Cloned rRNA gene sequences for the six organisms were aligned and compared. The data table, called a comparison matrix, summarizes the comparison of 617 nucleotide positions from the gene sequences. Each value in the table is the percentage of the 617 nucleotide positions for which both organisms in the pair have the same composition. Any positions that were identical across the rRNA genes of all six organisms were omitted from this comparison matrix.

Scientific Skills Exercises

Find the cell that represents the comparison of Comamonastestosteroni and Escherichia coli. What value is given in that cell?

a) 35

b) 52

c) 57

d) 61

Find the cell that represents the comparison of Comamonastestosteroni and Escherichia coli. What value is given in that cell?

a) 35

b) 52

c) 57

d) 61

What does the value 61 signify about the comparable rRNA gene sequences in Comamonas testosteroni and Escherichia coli?

a) that 61% of the 617 nucleotide positions are different between the two species

b) that 61 nucleotides are different between the two species

c) that 61 nucleotides are the same in both species

d) that 61% of the 617 nucleotide positions are the same in both species

What does the value 61 signify about the comparable rRNA gene sequences in Comamonas testosteroni and Escherichia coli?

a) that 61% of the 617 nucleotide positions are different between the two species

b) that 61 nucleotides are different between the two species

c) that 61 nucleotides are the same in both species

d) that 61% of the 617 nucleotide positions are the same in both species

Why do some cells have a dash rather than a value?

a) Those cells would compare one species to itself.

b) Those cells would duplicate comparisons shown elsewhere in the matrix.

c) Those comparisons were not made by the researchers.

Why do some cells have a dash rather than a value?

a) Those cells would compare one species to itself.

b) Those cells would duplicate comparisons shown elsewhere in the matrix.

c) Those comparisons were not made by the researchers.

Why are some cells shaded gray, with no value?

a) Those cells would compare one species to itself.

b) Those cells would duplicate comparisons shown elsewhere in the matrix.

c) Those comparisons were not made by the researchers.

Why are some cells shaded gray, with no value?

a) Those cells would compare one species to itself.

b) Those cells would duplicate comparisons shown elsewhere in the matrix.

c) Those comparisons were not made by the researchers.

Why did the researchers choose only one plant (wheat) to include in the comparison matrix?

a) A comparison matrix with more than six species is too unwieldy.

b) Wheat is the plant that is most closely related to bacteria.

c) Only one source of mitochondrial rRNA was needed to represent all mitochondria.

d) Wheat is the only plant with mitochondrial rRNA genes.

Why did the researchers choose only one plant (wheat) to include in the comparison matrix?

a) A comparison matrix with more than six species is too unwieldy.

b) Wheat is the plant that is most closely related to bacteria.

c) Only one source of mitochondrial rRNA was needed to represent all mitochondria.

d) Wheat is the only plant with mitochondrial rRNA genes.

Why did the researchers include five bacterial species in the comparison matrix?

a) They wanted to identify which bacterium is most closely related to the ancestor of mitochondria.

b) They wanted to identify how many of the five bacterial species have rRNA genes.

c) One of the species was a test, and the other four were controls.

d) They wanted to identify the evolutionary relationships among the five bacterial species.

Why did the researchers include five bacterial species in the comparison matrix?

a) They wanted to identify which bacterium is most closely related to the ancestor of mitochondria.

b) They wanted to identify how many of the five bacterial species have rRNA genes.

c) One of the species was a test, and the other four were controls.

d) They wanted to identify the evolutionary relationships among the five bacterial species.

Which bacterial species has an rRNA gene that is most similar to that of the wheat mitochondrion?

a) M. capricolum

b) A. tumefaciens

c) E. coli

d) C. testosteroni

e) A. nidulans

Which bacterial species has an rRNA gene that is most similar to that of the wheat mitochondrion?

a) M. capricolum

b) A. tumefaciens

c) E. coli

d) C. testosteroni

e) A. nidulans

The rRNA gene of A. tumefaciens is most similar to the wheat mitochondrial rRNA gene. What does that suggest?

a) that the alpha proteobacteria are more closely related to the ancestor of mitochondria than the other bacterial taxa

b) that the beta proteobacteria are more closely related to wheat than the other bacterial taxa

c) that the alpha proteobacteria are more closely related to wheat than the other bacterial taxa

d) that the beta proteobacteria are more closely related to the ancestor of mitochondria than the other bacterial taxa

The rRNA gene of A. tumefaciens is most similar to the wheat mitochondrial rRNA gene. What does that suggest?

a) that the alpha proteobacteria are more closely related to the ancestor of mitochondria than the other bacterial taxa

b) that the beta proteobacteria are more closely related to wheat than the other bacterial taxa

c) that the alpha proteobacteria are more closely related to wheat than the other bacterial taxa

d) that the beta proteobacteria are more closely related to the ancestor of mitochondria than the other bacterial taxa