Chapter 28: the Protists

Chapter 28: the Protists

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

• These amazing organisms belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists

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

Kingdom Protista??

• now part of the superkingdom Eukaryota– eukaryotes = true nucleus– evolution of a nucleus for the genetic information– evolution of membrane-bound organelles

• diverse group of single and colonial forms informally known as The Protists

• but Kingdom Protista really doesn’t exist anymore – too polyphyletic• probably arose from more than one prokaryotic group• 7 to 45 species recognized depending on zoologist• some as small as prokaryotes• molecular analysis has discovered many commonalities that make

them Protists

Protists– include groups that are photoautotrophs,

heterotrophs and mixotrophs• mixotrophs = combine photosynthesis and

heterotrophic nutrition– divide the protists into three categories:– 1. Photosynthetic – plant-like algae– 2. Ingestive – animal-like protozoans– 3. Absorptive – fungus-like

Cellular Anatomy

• most are unicellular– but the cellular composition is extremely complex

• unicellular protists carry out similar functions to multi-cellular eukaryotes with their organ systems– do so using subcellular organelles

• many of these organelles are seen in higher organisms

• other organelles are not found in the typical multicellular eukaryote– contractile vacuoles for osmoregulation

Protists and Eukaryotic Evolution

• Many components of the eukaryotic animal and plant cell were derived from protists

• diversity of protists has its origins in endosymbiosis• process where a unicellular organism engulfs another

cell – become endosymbionts and eventually a new organelle

Protists and Eukaryotic Evolution

• early evolution – ingestion of a photosynthetic cyanobacteria through primary endosymbiosis by a primitive eukaryote– eventual development into the plastids of the photosynthetic red and green algae

• Red and green algae also underwent secondary endosymbiosis• they themselves were ingested by another primitive eukaryotic cell to become eventual

plastids of the protists listed below in the figure

Cyanobacterium

Primaryendosymbiosis

Secondaryendosymbiosis



Heterotrophiceukaryote

Red algae

Green algae

Dinoflagellates

Plastid

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

The 5 Supergroups of Eukaryotes• 1. Excavata• 2. Chromalveolata

– the alveolates and stramenophiles• 3. Rhizaria• 4. Archaeplastida

– contains green algae and land plants• 5. Unikonta

– slime molds, entamoebas, fungi and animals

AlveolataDip

lom

onad

ida

Par

abas

ala

Eug

leno

zoa

Ancestral eukaryote

Stramenopila Amoebozoa (Opisthokonta) (Viridiplantae)Cer

cozo

a

Rad

iola

ria

Rho

doph

yta

Pla

nts

Chl

orop

hyte

s

Cha

roph

ycea

ns

Red

alg

ae

Met

azoa

ns

Fung

i

Cho

anof

lage

llate

s

Cel

lula

r slim

e m

olds

Pla

smod

ial s

lime

mol

ds

Gym

nam

oeba

s

Ent

amoe

bas

Rad

iola

rians

Chl

orar

achn

ioph

ytes

Fora

min

ifera

ns

Bro

wn

alga

e

Gol

den

alga

e

Oom

ycet

es

Dia

tom

s

Cili

ates

Api

com

plex

ans

Eug

leni

ds

Din

ofla

gella

tes

Kin

etop

last

ids

Dip

lom

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s

Par

abas

alid

s

Excavata Chromalveolata UnikontaRhizaria Archaeplastida

Ani

mal

ia

Chl

orop

hyta

Eukaryotic Phylogenetic Tree

Fung

i

Pla

ntae

Cha

roph

yta

Clade: Excavata

• A. Diplomonads• B. Parabasilids • C. Euglenozoans

Clade: Excavata

• Diplomonads & Parabasilids – protists in these two clades lack plastids (no photosynthesis) – mitochondria do not have DNA or the enzymes for the citric acid cycle or

proteins for the electron transport chain

Clade: Excavata

• A. Diplomonads– two equal-sized nuclei and multiple flagella

– flagella is very different from prokaryotic flagella

– have modified mitochondria = mitosomes

– many are parasites

giardia intestinalis

• B. Parabasalids– also have reduced/modified mitochondria = hydrogenosomes

– include the protists called trichomonads – Trichomonas vaginalis

– mobility through an undulating membrane in addition to flagellaLE 28-5b

Flagella

Trichomonas vaginalis, a parabasalid (colorized SEM)

Undulating membrane 5 µm

• C. Euglenozoans– belong to a diverse clade – includes heterotrophs, photosynthetic

autotrophs and parasites– considered a photosynthetic protist similar to algae– like algae – the photosynthetic protists have chlorophyll a and b in

chloroplasts– distinguishing feature – a rod with either a spiral or crystalline structure

inside each of their flagella

– divided into the groups: – 1. the Kinetoplastids – 2. the Euglenoids

1. Kinetoplastids - Trypanosomes– used to be called the zoomastigophores– defined by a single, large mitochondrion that contains an organized mass of DNA

= kinetoplast– free-living forms in freshwater, marine and soil – feed on the prokaryotes in

these ecosystems– some are parasites of animals, plants and other protists

• Trypanosoma gambienese – sleeping sickness (neurological disease) & Chagas’ disease (congestive heart failure) in humans

Kinetoplastids: Trypanosoma

Life cycle-cycles between the tse tse fly and the human-different forms of the trypanosome depending on what host and where it is in the host

1. fly injects the trypanosome2. multiplication in the human

host – e.g. in the blood3. bit by fly and transfer4. multiplication in the fly’s gut

and then in the salivary gland

– unicellular protist – most are autotrophic

• several chloroplasts with chlorophyll a and b and carotenoid pigments

• some can also be mixotrophic – photosynthetic in sunlight, engulfs prey in absence of sunlight

– main characteristic - two flagella that emerge from a “pocket” structure

• at the pocket is a large contractile vacuole that connects to the outside

• continuously collects water from the cell and returns it to the outside – regulates osmotic pressure

• two flagella arise at this reservoir• only one emerges from the canal and actively beats

for locomotion

2. Euglenoids – The Euglena

used to be classified as the Class Phytomastigophorea

– inside the plasma membrane is a structure called the pellicle

• articulated strips of protein lying side by side• elastic enough to enable turning and flexing of the

protist• but rigid enough to prevent major changes in shape

– eyespot (stigma) - near the flagella• functions as a pigment shield allowing only certain

wavelengths of light to strike the light detector– light detector (photoreceptor) – detects the filtered

light and results in movement toward the light direction

• probably developed in order to maximize its photosynthetic potential

2. Euglenoids

used to be classified as the Class Phytomastigophorea

Clade: Chromalveolata

• originated more than a billion years ago when their ancestor ingested a photosynthetic red algae (via secondary endosymbiosis)– plastids within these protists have red algae origins (DNA analysis)– divided into two major groups:

• 1. Alveolates • 2. Stramenophiles

Clade: Chromalveolata

– A. Alveolates:• 1. Dinoflagellates• 2. Apicomplexans• 3. Ciliates

– B. Stramenophiles• 1. Diatoms• 2. Golden Algae• 3. Brown Algae• 4. Oomycetes

Chromalveolata - A. Alveolates

• characterized by membrane-bound sacs called alveoli– just under the plasma membrane– function unknown

• 1. Dinoflagellates – move through flagellar action• 2. Apicomplexans - parasites• 3. Ciliates – move through ciliary action

Alveolates: 1. Dinoflagellates

• several thousand species– “dinos” = whirling– components of both marine and freshwater

phytoplankton– possess characteristic shapes – reinforced by internal

plates of cellulose that become encrusted with silica - act as “armor”

– some can be heterotrophic (phagocytic) – most are autotrophic with well-formed plastids for

photosynthesis– possess mitochondria with tubular cristae (similar to

animals)– two flagellae – located in perpendicular grooves in

these plates• one groove is transverse = cingulum – propels the

dinoflagellate forward and causes it to spin• other groove is longitudinal = sulcus – acts as the

rudder

LE 28-10

3 µm

Flagella

– capable of proliferating explosively – “blooms” • “red tide” (carotenoid pigments found in the plastids) - produce a

toxin that kills off invertebrates– some can be bioluminescent – ATP driven reaction that creates a

glow at night• may be a defense mechanism

Alveolates: 2. Apicomplexans• nearly all are animal parasites• spread through the formation of tiny infectious cells = sporozoites• named because one end (apex) contains a complex of organelles

specialized for penetrating host tissues and cells• have a non-photosynthetic plastid = apicoplast which has many

functions including the synthesis of fatty acids for its membranes• life cycle – includes sexual and asexual stages

– requires more than one host to complete

Alveolates: 2. Apicomplexans• best known is the Plasmodium – causes malaria

– rivals tuberculosis as the leading cause of human death by infectious disease

– can be reduced by insecticides that kill the Anopheles mosquito (DDT) and by drugs that kill the Plasmodium (quinine based drugs)

– vaccines hard to develop – Plasmodium lives inside the RBC (hidden)– carriers of sickle cell anemia gene – resistant to malaria

Plasmodium Life Cycle

• 1. infected Anopheles mosquito bites a person injecting its sporozoites (n)

• 2. sporozoites enter the liver and undergo division to become merozoites (n)

– merozoites enter RBCs by using their apical complex • 3. the merozoites asexually divide to make

more– some go on to infect more RBCs

• 4. other merozoites develop into gametocytes• 5. gametocytes picked up by a new mosquito• 6. gametes form and fertilization takes place in

the mosquito’s digestive tract– the fertilized cell = zygote

• 7. an oocyst develops from the zygote and adheres to the wall of the mosquito’s gut

– produces more sporozoites– these are delivered to a new human host when

the mosquito bites another human

LE 28-11

Sporozoites(n)

Inside mosquito

Oocyst

Zygote(2n)

MEIOSIS Merozoite(n)

Livercell

Liver

FERTILIZATION

GametesGametocytes(n)

Red bloodcells

Inside humanMerozoite

Apex

Red bloodcell

0.5 µm

Haploid (n)

Key

Diploid (2n)

Alveolates: 3. Ciliates - Paramecium• use of cilia to move and feed

– cilia may completely cover the protist or may cluster in a few rows or tufts

• distinguished by the presence of two types of nuclei: macronucleus (large) and micronucleus (small)– may have one or more of each type– macronucleus – contains dozens of copies of the genome

• control the everyday functions of the ciliate– micronucleus – function in reproduction

• exchanged between two ciliates during conjugation

LE 28-12

FEEDING, WASTE REMOVAL, AND WATER BALANCE

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.

Paramecium

• freshwater protist – constantly takes on water from its hypotonic environment

• they contain contractile vacuoles for the regulation of osmotic pressure – accumulate excess water via radial canals and then expel it through the plasma membrane back into the environment

• cilia participate in movement– but also gather food and move it

toward the oral groove which holds the cell mouth at the bottom

– food is then engulfed into a food vacuole via phagocytosis

• food vacuoles combine with lysosomes containing digestive enzymes– undigested food particles are

carried to the opposite end of the cell as the cell mouth

– fuse with the plasma membrane in a specific region – acts as an “anal pore”

FEEDING, WASTE REMOVAL, AND WATER BALANCE

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.

Paramecium

Paramecium CONJUGATION AND REPRODUCTION

MEIOSIS

MICRONUCLEARFUSION

Haploidmicronucleus

Diploidmicronucleus

Diploidmicronucleus

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.

• asexual reproduction – through binary fission

• sexual reproduction involves conjugation– 1. two compatible mating strains align

side by side and partially fuse – 2. meiosis of their micronuclei

produces a total of 4 haploid micronuclei in each cell

– 3. three micronuclei in each disintegrate & the remaining micronuclei in each divides by mitosis- resulting in 2 micronuclei in each paramecium

– 4. the cells swap one of their micronuclei – genetic recombination

– 5. the cells separate

Paramecium CONJUGATION AND REPRODUCTION

MEIOSIS

MICRONUCLEARFUSION

Haploidmicronucleus

Diploidmicronucleus

Diploidmicronucleus

Compatiblemates


Macronucleus




The cells separate.


Reproduction

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



– 6. the two micronuclei in each cell fuse to produce a diploid nuclei

– 7. three round of mitosis without fission results in 8 micronuclei in each paramecium

– 8. the original macronuclei disintegrates and 4 micronuclei become 4 macronuclei to replace it – leaves 4 micronuclei

– 9. two rounds of binary fission now happen results in 4 daughter cells

– 10. the micronuclei (4) and macronuclei (4) then partition into the four daughter cells – each paramecium ends up with 1 micronuclei and 1 macronuclei

Got all that?? CONJUGATION AND REPRODUCTION

MEIOSIS

MICRONUCLEARFUSION

Haploidmicronucleus

Diploidmicronucleus

Diploidmicronucleus

Compatiblemates


Macronucleus




The cells separate.


Reproduction

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



-partially fuse-1 micronuclei becomes 4 via meiosis (haploid)-3 disappear-1 micronuclei becomes 2 via mitosis-paramecia “swap” 1 micronuclei and separate-fuse 2 micronuclei into 1 (diploid)-2 micronuclei become 8 (mitosis/no cytokinesis)-macronuclei disappears-so 4 of the 8 micronuclei develop into 4 macronuclei-4 of the micronuclei stay micronuclei-2 rounds binary fission 4 daughter paramecia-each daughter cell gets a macronuclei and a micronuclei

Chromalveolata - B. Stramenophiles• stramen = “straw”; pilos – “hair”• comprised of several groups of heterotrophs and several groups of

phototrophs (considered to be algae)• flagella are said to be “hairy” – have numerous hair-like projections along the

length• this hairy flagellum is paired with a smooth flagellum• 1. oomycetes – water molds• 2. bacillariophytes - diatoms• 3. chrysophytes – golden algae• 4. charophyceans – brown algae

Smoothflagellum

Hairyflagellum

5 µm

What is Algae??• photsynthetic protists• algae = eukaryotic organism with chlorophyll a pigments that carry

out oxygen-producing photosynthesis• study of algae = phycology• no longer any formal classification schemes

– algae are scattered across many phyla = polyphyletic• BUT They differ from plants – lack a well-organized vascular system

and they have a simple reproductive system• occur most often in water

– fresh and marine – may be suspended as planktonic organisms or attached to the bottom (benthic)

Algae: Photosynthetic Protists

• algae frequently confused with plankton• plankton = free-floating microscopic aquatic organisms

– phytoplankton – made up of algae and small plants– zooplankton – non-photosynthetic protists and animals

• classical algae are now grouped together with the plants - Phyla Chlorophyta

• some are a separate lineage - known as red algae– Phylum Rhodophyta

• some are grouped with the stramenophiles - yellow and brown algae– Phyla Chrysophyta and Phaeophyta

• important properties that classify them:– 1. cell wall composition – rigid cell wall

• some have an outer membrane outside the wall – similar to the bacterial capsule– 2. the form in which food is stored– 3. chlorophyll molecules and accessory pigments (carotenoids)

• chloroplasts are found in membrane-bound sacs (thylakoids) for the light-reactions of photosynthesis

– 4. flagella number and location of their insertion into the cell• flagella are used for locomotion

– 5 morphology of the cells and/or body • comprised of a vegetative body = thallus


• important properties that classify them:– 6. habitat: marine or freshwater

• unicellular, colonial, filamentous, membranous, blade-like or tubular– 7. reproductive structures: reproduction is asexual or sexual

• asexual – seen in unicellular forms• sexual – generation of eggs by oogonia or sperm by antheridia

– 8. mitochondria cristae structure: tubular, disc or plate-like (lamellar)


Stramenophiles: 1. Oomycetes: Water molds

water mold

• oomycete = “egg fungus”• water molds, white rusts and downey mildews

– white rusts and downey mildews live as parasites on land plants

– e.g. Potato blight - Phytophthora infestans

water mold

• used to be considered fungi – have multinucleate filaments called hyphae that resemble those seen in fungi

• but the oomycetes have cell walls made of cellulose (fungus – chitin) and the diploid condition predominates (reduced in fungi)

• molecular data also cannot confirm fungal origins• similarities are an example of convergent evolution• do not carry out photosynthesis – non-autotrophic• acquire nutrients as decomposers – grow as cottony

masses on dead animals and algae = heterotrophic

Stramenophiles: 1. Oomycetes: Water molds

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

• life cycle: can alternate between asexual and sexual forms– a zoospore develops via mitosis into a hyphae – the zoospore is biflagellated with one smooth flagella and the other “hairy”

• so it is a stramenophile– these hyphae will develop zoosporangia at their tips - produce zoospores

asexually (i.e. mitosis)– but hyphae can also develop sexual structures that produce gametes via

meiosis

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

• life cycle: sexual – one region of the hyphae undergoes meiosis to

produce egg nuclei (n) within a structure called an oogonium

– other branches can develop sperm nuclei (n) via meiosis – contained within an antheridial hyphae

– these antheridial hyphae grow and “hook” around the oogonium and deposit their nuclei through fertilization tubes = fertilization

– the hyphae then becomes dormant – when the wall of the oogonium breaks apart and

releases the zygotes – they zygotes germinate to regenerate hyphae

– new hyphae develop into a new sexual structures – however some zygotes can form a zoosporangium

which produces zoospores asexually

Stramenophiles: 2. Diatoms• 100,000 species of unicellular algae • with a unique glass-like wall made of silica embedded in an

organic matrix– two parts that overlap like a shoe box and lid– upperlid = epitheca, lowerlid = hypotheca– effective protection against extreme crushing forces

• reproduce asexually via mitosis– daughter receives half of the parental cell wall and generates a

new half• sexual reproduction is not common • photosynthetic – chlorophylls a and c and carotenoids• some are heterotrophic – absorb carbon-containing molecules

through holes in their walls

Stramenophiles: 2. Diatoms• major component of phytoplankton in fresh and marine

environments in cooler waters– source of food for fish and other marine animals– upon death –sink to the bottom = diatomaceous earth– active ingredient in detergents, fine abrasive polishes, paint

removers, decoloring oils, filtering agents, components of insulation and soundproofing products, reflective paint additive

• modern uses in nanotechnology – mechanism of assembly of their cell walls is being used as a model for miniature models and lasers

Stramenophiles: 3. Golden Algae -Phylum Chrysophyta• all species are photosynthetic • but some can be mixotrophic by also absorbing

dissolved organic compounds or ingesting food particles by phagocytosis

• major photosynthetic pigments: chlorophylls a and c + carotenoids

– stored in plastids• dominant pigment is a carotenoid called fucoxanthin

– golden-brown color• some have cell walls• some have intricate external coverings = scales, walls

and plates• most are unicellular but some are colonial • most are biflagellated – both attached near one end

of the cell

Dinobryon

Stramenophiles: 4. Brown algae - Phylum Phaeophyta

• brown algae – most complex algae– all are multicellular and all are

marine– some have the most complex

multicellular anatomy of all algae– some have specialized tissues like

animals and plant– include the seaweeds– giant seaweeds in intertidal zones –

kelps

LE 28-18

Blade

Stipe

Holdfast

Brown algae Thallus

4. Brown algae: Phaeophyta

• brown algae – composed of a thallus = algal body that

is plant-like– thallus has a rootlike hold-fast which

anchors the seaweed and a stem-like stipe that supports leaf-like blades

– BUT there are no true roots, stems and leaves!

– blades – surface for photosynthesis– blades can come equipped with floats

to keep them near the surface

LE 28-18

Blade

Stipe

Holdfast

Brown algae Thallus

Brown algae: Life cycle

Developingsporophyte

Zygote(2n)

FERTILIZATIONMature femalegametophyte(n)

Egg

Sperm

MEIOSIS

Haploid (n)

Key

Diploid (2n)

Sporangia

Sporophyte(2n)

Zoospores

Female

Gametophytes(n)

Male

e.g. Laminaria

• brown algae exhibit alternation of generations– alternate between haploid and

diploid multicellular forms– only applies to multicellular stages in

the life cycle– if the two multicellular forms are

structurally different = heteromorphic

– two forms seen:• A. diploid sporophyte – for the

production of haploid spores via meiosis

• B. haploid gametophytes – for the production of haploid gametes via mitosis

An overview of Alternation of Generations1. the spores develop into

gametophytes (n)2. the gametophytes make gametes (n)3. the gametes fuse and regenerate the

diploid sporophyte (2n)

Brown algae: Life cycle

Developingsporophyte

Zygote(2n)

FERTILIZATIONMature femalegametophyte(n)

Egg

Sperm

MEIOSIS

Haploid (n)

Key

Diploid (2n)

Sporangia

Sporophyte(2n)

Zoospores

Female

Gametophytes(n)

Male

e.g. Laminaria

– life cycle starts with the diploid sporophyte – adult algae with hold-fast, stipe and blades

– 1. on the blade of the sporophyte – development of sporangia

– 2. sporangia develop haploid zoospores by meiosis

– 3. 50% of zoospores develop into male gametophytes and 50% into female gametophytes

• both are multicellular but still haploid– 4. the gametophytes produce gametes via

mitosis – 5. gametes are released and fuse to form the

diploid zygote– 6. zygote develops into a new sporophyte

which grows via mitosis to form a new adult algae

Clade Rhizaria

• characterized by the presence of threadlike pseudopodia = extensions of the cytoplasm that bulge anywhere along the cell’s surface– “false –feet”– used in locomotion and prey capture– extend and contract by reversible assembly of actin subunits into microfilaments– first formed through the projection of a lamellipodium – actin assembles in the leading

edge until it forms a microfilament network• cytoplasm flows in forming the pseudopodium

– locomotion: anchor a tip to the surface – stream cytoplasm into the pseudopodium – prey capture: pseudopodia senses the prey through physical contact and surrounds it

Clade Rhizaria

– several types of pseudopodia seen in this Clade:• 1. Lobopodia – blunt shaped

– possess forms of cytoplasm called ectoplasm and endoplasm

– locomotion and feeding• 2. Filopodia – football shaped

– ectoplasm only, two-way streaming to move food like a conveyor belt

• 3. Reticulopodia – branching filopodia– primarily used for feeding

• 4. Axiopodia – long and thin– reinforced by microtubules– responsible for phagocytosis NOT locomotion

– pseudopodia used to classify the members of this clade

• A. Radiolarins• B. Forams• C. Cercozoans

Clade Rhizaria

• A. Radiolarians: delicate, intricately symmetrical internal skeletons made of silica– axiopodia which “radiate” out from a central body – reinforced by microtubultes– pseudopodia are also capable of phagocytosing food – cytoplasmic streaming then

carries the food into the central body

LE 28-23

200 µmAxopodia

Radilarins

Clade Rhizaria

• B. Forams: formerly called foraminiferans– named for their porous shells – holes in the shells are called foramina– shell is called a test = single piece of organic material hardened with calcium carbonate– pseudopodia extend through the holes – function in swimming, in making the test and

feeding– marine and freshwater – found in sand or attached to rocks or algae

Forams

C. Cercozoans: The Amoeba• contain the organisms called amoebae• amoeba species are also found in other clades• most are heterotrophs – many are parasites of plants and animals• some can be predators!

– predators of bacteria

Clade Archaeplastida

• more than a billion years ago – heterotrophic protist acquired a cynanobacterial endosymbiont– gave rise to red algae and green algae

• these cyanobacteria evolved into plastids– numerous functions: photosynthesis and storage

• 475 million years ago – green algae ancestors evolved into land plants

• red algae, green algae and land plants are now placed into the same clade based on molecular data – Archaeplastida

Cyanobacterium

Primaryendosymbiosis

Heterotrophiceukaryote

Red algae

Green algae

Plastid

Plastid

Clade Archaeplastida

• Archaeplastida can be divided into:• A. Red algae – Phylum Rhodophyta• B. Green algae – Phylum Chlorophyta• C. Charophytes – includes Plants; Phylum Charophyta

Archaeplastida - A. Red Algae: Phylum Rhodophyta

• red algae – 6000 species– multicellular algae– most are autotrophic – photosynthesis– possess plastids that contain numerous pigments– red pigment = phycoerythritin and blue pigment = phycocyanin (phycobilins)– pigments allow for the absorption of green and blue light which have long wavelengths and

can penetrate the deeper waters where the red algae are found• blue and red wavelengths are absorbed by the phycobilins and the light energy is then transferred to

the chlorophylls for photosynthesis

• red algae – 6000 species– sugar storage form = floridean– some can be parasitic on other algae – because they lack pigmentation for photosynthesis– cell wall includes a matrix of proteins and sugars

• this matrix is also called agar = polymers of galactose– largest red algae are included in a group called seaweeds (e.g. nori)– life cycle does not include a flagellated step – must rely on ocean currents to deliver

gametes for fertilization

Archaeplastida - A. Red Algae: Phylum Rhodophyta

Archaeplastida - B. Green algae: Phylum Chlorophyta

• green algae– named for the green chloroplasts – contain chlorophyll pigments that are very similar to

plants– chloroplasts also have a similar structure to plants

• thylakoid membranes– divide into two groups:– 1. Charophytes – most closely related to plants– 2. Chlorophytes – 7000 species of green algae

Archaeplastida - B. Green algae: Phylum Chlorophyta

• green algae– 2. Chlorophytes – 7000 species

• chloro = “green”• mostly freshwater• chlorophylls a and b + carotenoid pigments• sugar storage form = starch• cell walls made of cellulose• most are unicellular

– can live symbiotically with other eukaryotes – contributing to their photosynthetic output

• can also live symbiotically with fungus – as lichens• some are also multicellular - colonial, filamentous (pond scum) and

sheet-like forms

Unicellular Green Algae

• e.g. Chlamydomonas – example of a unicellular algae

– two flagella of equal length at the anterior end

– one conspicuous pyrenoid» organelle found in or beside the

chloroplasts of algae» involved in carbohydrate synthesis

– eyespot or stigma» movement towards light

– two small contractile vacuoles at the base of the flagella – function as osmoregulatory organs

– asexual reproduction– sexual reproduction is also possible – cell

division produces gametes of each “sex”

Green algae: Life Cycle

MEIOSIS

Haploid (n)

Key

Diploid (2n)

SYNGAMY

SEXUALREPRODUCTION

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

Zygote(2n)

Regionsof singlechloroplast

Nucleus

Flagella

Cell wall

1 µm

– life cycle: sexual and asexual stages• mature green algae cells are haploid – single cell with a cup-like chloroplast

and 2 flagellae• asexual reproduction: the cell reabsorbs its 2 flagellae and divides by

mitosis to form four identical cells (zoospores) within a capsule– cells are released as swimming zoospores new mature green algae

MEIOSIS

Haploid (n)

Key

Diploid (2n)

FERTILIZATION

SEXUALREPRODUCTION

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

Zygote(2n)

Regionsof singlechloroplast

Nucleus

Flagella

Cell wall

1 µm

• sexual reproduction: happens upon shortage of nutrients – haploid zoospore develops into male and female gametes– gametes of opposite mating types fuse to form the zygote (diploid + 4 flagella)– zygote loses its flagellae and surrounds itself by a coat to protect itself– meiosis in the zygote results in 4 haploid cells – two from each mating type– these released haploid cells develop into bi-flagellated mature cells that can continue the

sexual life cycle or reproduce asexually

Green algae: Life Cycle

Colonial Green Algae• not really multicellular• colony of unicellular algae

– e.g. Volvox• colony or 500 to 60,000 cells – mostly small vegetative cells

– individual cells resemble Chlamydomonas – bi-flagellated– flagella all beat in a coordinated fashion – rotates the colony in a clock-wise

fashion• cells are interconnected by thin strands of cytoplasm• cells have eyespots – will orient toward the light• some cells reproduce asexually• some cells are reproductive - develop from the cells at the equator = called gonads

– produce gametes that undergo fertilization within the colony– produce a zygote

• zygote undergoes mitosis to form a small daughter colony• the daughter colony remains in the parental colony until it bursts free

Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells 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.

Clade Unikonta• recently proposed clade• supergroup of eukaryotes that includes animals, fungi and

some protists• means “one flagella”• two major clades:• A. Amoebozoans: the amoebas & slime molds• B. Opisthokonts: fungi and animals

Unikonta: A. Amoebozoans• have lobe or tube-shaped pseudopodia rather than threadlike• three types of Amoebozoans:

• 1. Gymnamoebas– unicellular, one flagella– soil, freshwater and marine– most are heterotrophic – consume bacteria and other protists plus detritus

(decomposers)– some can possess shells = tests

• 2. Entamoebas– parasitic amoebae– infect all classes of vertebrates and some invertebrates– humans are host to at least 6 species– Entamoeba histolytica – amoebic dysentery

• third leading cause of death in the world due to parasites – 100,000 deaths each year

• 3. Mycetezoans = Slime molds– cellular slime molds– plasmodial slime molds

Unikonta: A. Amoebozoans

Plasmodial slime molds

1 mm

MEIOSIS Haploid (n)

Key

Diploid (2n)

Zygote (2n)

FERTILIZATION

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Stalk

Amoeboid cells(n)

GerminatingsporeFlagellated cells

(n)

• brightly pigmented – orange or yellow• named for the formation of a feeding stage = plasmodium in the life cycle• capable of moving over a substrate – via cytoplasmic streaming• plasmodium – very large but still is unicellular

– single cell undergoes mitosis but fails to divide through cytokinesis – “super-cell”– lives on organic matter – takes in through phagocytosis

• takes on a web-like form and undergoes sexual reproduction when conditions become harsh• plasmodium develops fruiting bodies or sporangium via meiosis which release haploid spores (n)• germination of the spores takes place in the presence of adequate moisture

– results in the production of either amoeboid cells (myxoamoebae) or flagellated cells (swarm cells) – both are haploid– fertilization (syngamy) requires the fusion of the same type of cell – i.e. swarm with swarm

• production of the zygote (2n) and development of a new plasmodium forms

Cellular slime molds

600 µm

MEIOSIS

Haploid (n)Key

Diploid (2n)

Zygote (2n)

FERTILIZATION

Migratingaggregate

Emergingamoeba

SEXUALREPRODUCTION

Amoebas

Spores(n)

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodies

Aggregatedamoebas

200 µm

• feeding stage is a solitary amoeboid form = myxoameoba• can undergo asexual or sexual reproduction• sexual reproduction: takes place in presence of abundant food

– two haploid myxoamoebae fuse and form the zygote (2n)– the zygote engulfs more haploid amoebae to grow larger– forms a protective cell wall and begins to divide back into numerous haploid amoebae – the newly formed amoebae are released when the cell wall bursts

Cellular slime molds

600 µm

• asexual reproduction: occurs upon food depletion– aggregation of hundreds of amoebae and their migration = multicellular aggregate called a

pseudoplasmodium– the pseudoplasmodium is capable of migration – once it stops moving – some amoebae differentiate into a stalk, others differentiate into an asexual fruiting

body and form spores (n) = sorus or the sorocap– spores are released from the sorus– in the presence of food – haploid myxoamoebae emerge from spores and being to feed

MEIOSIS

Haploid (n)Key

Diploid (2n)

Zygote (2n)

SYNGAMY

Migratingaggregate

Emergingamoeba

SEXUALREPRODUCTION

Amoebas

Spores(n)

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodiesAggregatedamoebas

200 µm

Sorus

pseudoplasmodiumpseudoplasmodium

Documents

Chapter 28: the Protists