Lecture #3

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• include the algae and slime molds• first observed in pond water by Antoni van Leeuwenhoek 300 years

ago• 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 or algae– 2. Ingestive – animal-like or protozoans

• amoeba

– 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

– endoplasmic reticulum– Golgi apparatus– lysosomes

• 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– e.g. acquisition of mitochondria – ingestion by alpha-proteobacteria by an ancestral cell

• early evolution – ingestion of a photosynthetic cyanobacteria through primary endosymbiosis by a heterotrophic eukaryote

– eventual development into the plastids of the photosynthetic red and green algae– DNA of red and green algae is very similar to that of cyanobacteria– plastid membrane is dual layered – similar to the inner and outer membranes of the cyanobacteria

• Red and green algae also underwent secondary endosymbiosis – they were ingested by a heterotrophic eukaryotic cell to become endosymbionts and eventual plastids of the protists listed below in the figure

Cyanobacterium

Primaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Heterotrophiceukaryote

Red algae

Green algae

Dinoflagellates

Plastid

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

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

– common ancestors – 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

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s

Cha

roph

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ns

Red

alg

ae

Met

azoa

ns

Fun

gi

Cho

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lage

llate

s

Cel

lula

r sl

ime

mol

ds

Pla

smod

ial s

lime

mol

ds

Gym

nam

oeba

s

Ent

amoe

bas

Rad

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rians

Chl

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achn

ioph

ytes

For

amin

ifera

ns

Bro

wn

alga

e

Gol

den

alga

e

Oom

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Dia

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Cili

ates

Api

com

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ans

Eug

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ds

Din

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gella

tes

Kin

etop

last

ids

Dip

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Par

abas

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s

Excavata Chromalveolata UnikontaRhizaria Archaeplastida

Ani

mal

ia

Chl

orop

hyta

Eukaryotic Phylogenetic Tree

Fun

gi

Pla

ntae

Cha

roph

yta

Clade: Excavata

• A. Diplomonads• B. Parabasilids • C. Euglenozoans• 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– cannot use O2 to help extract energy from carbohydrates– therefore they are found in anaerobic environments

• A. Diplomonads– two equal-sized nuclei and multiple flagella– flagella is very different from prokaryotic flagella

• eukaryotic flagella is an extension of the cytoplasm and are made of microtubules composed of tubulin in a distinct 9+2 array pattern

– have modified mitochondria = mitosomes– many are parasites

• e.g. giardia intestinalis – intestinal protist in contaminated drinking water – severe diarrhea

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

• generate some energy anaerobically – releasing H2 gas as a by-product– include the protists called trichomonads – Trichomonas vaginalis

• disturbance in the normal pH of the vagina allows this protist to outcompete beneficial microbes and infect the vaginal lining – sexually transmitted to males also

• probable acquisition of parasitic behavior through genetic recombination (conjugation) with a parasitic bacteria also within the vagina

– mobility through an undulating membrane in addition to flagella

LE 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– 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• unknown function

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

1. Kinetoplastids– 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

• Coated with millions of copies of a single protein• Evade detection by the host using a “bait and switch” mechanism which

allows the trypanosome to change the composition of theis surface protein to a different molecular structure

• about 1/3 of the trypanosomes genome is devoted to making these surface proteins!

Kinetoplastids: Trypanosoma

– unicellular protist with 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– 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

– 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 cell• 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: Alveolates & Stremenophiles– A. Alveolates:

• 1. Dinoflagellates• 2. Apicomplexans• 3. Ciliates

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

A. Alveolates

• characterized by membrane-bound sacs called alveoli– just under the plasma membrane– function unknown – may be involved in the stabilization of the

cell membrane or may regulate the entrance and exit of ions and water (osmolarity)

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

1. Dinoflagellates• Dinoflagellates – several thousand species– “dinos” = whirling– components of both marine and

freshwater phytoplankton– some can be heterotrophic (phagocytic) – most are autotrophic with well-formed

plastids for photosynthesis• chlorophylls a and c + carotenoids and

xanthophylls – yellowish green color– possess mitochondria with tubular cristae

(similar to animals)– characteristic shapes – reinforced by

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

LE 28-10

3 µ

m

Flagella

– 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

– capable of proliferating explosively – “blooms” • “red tide” (carotenoid pigments found in the plastids) can result from

blooms of certain dinoflagellates – 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• if the water is lit-up by predators that eat dinoflagellates – it may

attract fish to eat those predators

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• 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 killed by the “leakiness” of the affected RBCs

Plasmodium

• Sexual and asexual reproduction that requires more than one host to complete

• 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 into more merozoites – every 48 to 72 hrs – merozoites will break

out of some RBCs – fever and chills– some will go on to infect more RBCs and

multiply• 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

LE 28-11

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)

3. Ciliates• 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

• not organized as chromosomes • packed into smaller units each bearing duplicates of just a few genes• 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”

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 involving 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 of these in each disintegrate & the remaining micronuclei in each divides by mitosis- resulting in 2 micronuclei in each

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

– 5. the cells separate– 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 ends up with 1 micronuclei and 1 macronuclei

-partially fuse-1 micronuclei becomes 4 haploid micronuclei (meiosis)-3 disappear-1 micronuclei becomes 2 (mitosis)-“swap” 1 micronuclei and separate-fuse 2 micronuclei into 1 (diploid)-2 micronuclei become 8 (mitosis/no division)-macronuclei disappears-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

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

phototrophs (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

Algae: Photosynthetic Protists• study of algae = phycology• no longer any formal classification schemes

– scattered across many phyla = polyphyletic• algae = eukaryotic organisms with chlorophyll a pigments that carry out

oxygen-producing photosynthesis• differ from the plants – lack a well-organized vascular system and they have a

simple reproductive system• reproduce sexually and asexually• occur most often in water

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

• plankton = free-floating microscopic aquatic organisms– phytoplankton – made up of algae and small plants– zooplankton – non-photosynthetic protists and animals

• some classical algae are now grouped together with the plants (green algae), some are a separate lineage (red algae), some are grouped with the stremenophiles (yellow and brown algae, diatoms), some are grouped with the alveolates (diatoms) and some with the protozoans (euglenoids)

• 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. form in which food is stored– 3. chlorophyll molecules and accessory pigments (carotenoids)

• chloroplasts have 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

– 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• three forms: 1. fragmentation, 2. spores and 3. binary fission• sexual – generation of eggs within modified vegetative cells (oogonia) or sperm by

antheridia– 8. mitochondria cristae structure: tubular, disc or plate-like (lamellar)– chlorophyta, charophyta, euglenophyta, chrysophyta, phaeophyta, rhodophyta,

pyrrophyta

Algae: Photosynthetic Protists

1. Oomycetes: Water molds

water mold

Water mold oogonium• oomycete = “egg fungus”• water molds, white rusts and downey mildews• 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• derived from a plastid containing ancestor - no longer

have plastids and do not carry out photosynthesis – non-autotrophic

• acquire nutrients as decomposers – grow as cottony masses on dead animals and algae = heterotrophic

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

– Phytophthora infestans – potato blight– contributed to the Irish famine of the 19th century– today still leads to crop losses of close to 15% (North

America) and as high as 70% (Russia)– molecular engineers have transferred blight-resistant

genes into domestic potato crops to protect them

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

– asexual cell called a zoospore develops via mitosis into a hyphae

– the zoospore is biflagellated with one smooth flagella and the other “hairy”

– this hyphae develops sexual structures that produce gametes or alternatively can form zoospores asexually

– in the sexual life cycle - 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 antitheridial hyphae

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

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

– these zygotes germinate to regenerate hyphae which then develops into a new sexual structure – completes the sexual life cycle

– however some zygotes will form a zoosporangium which produces zoospores asexually

– germination of these zoospores starts the asexual life cycle

Water mold zoospores

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– wall is a lacework of holes and grooves

• 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• 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– not broken down by decomposers – carbon remains on the sea floor and is not released as

CO2– may be able to decrease global warming – by taking CO2 out of the environment– active ingredient in detergents, fine abrasive polishes, paint removers, decoloring oils, filtering

agents, components of insulation and soundproofing products, reflective paint additive• store their food reserves in the form of a glucose polymer = laminarin• modern uses in nanotechnology – mechanism of assembly of their cell walls is being

used as a model for miniature models and lasers

3. Golden Algae: Chrysophyta• all species are photosynthetic but some can be

mixotrophic by absorbed dissolved organic compounds or ingesting good particles by phagocytosis

• major photosynthetic pigments: chlorophylls a and c + carotenoids (fucoxanthin)

• dominant pigment is fucoxanthin – golden-brown color

• major carbohydrate reserve = chrysolaminarin• 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

4. Brown algae: Phaeophyta

• brown algae – most complex algae– all are multicellular and 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– carotenoid pigments located in plastids

also found in the golden algae and diatoms

– sugar storage form = laminarin– 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

– alternation between haploid and diploid multicellular forms

– only applies to multicellular stages in the life cycle

– if the two multicellular forms are structurally different = heteromorphic

– 1. diploid multicellular individual = sporophyte – adult algae with hold-fast, stipe and blades

– 2. on the blade – development of sporangia from the sporophyte

– 3. sporangia develop haploid zoospores by meiosis

– 4. 50% of zoospores develop into male gametophytes and 50% into female gametophytes – these are multicellualr

– 5. the gametophytes produce and release the gametes that will fuse and form the zygote

• eggs remain attached to the female gametophyte• eggs can release a chemical that will attract sperm

– 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

• contraction requires interaction between actin and myosin

– 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– types of pseudopodia:

• 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– complex and bear individual pseudopodia that form an irregular net– used for primarily ingestion, can be used for locomotion

• 4. Axiopodia – long and thin– reinforced by microtubule arrays enveloped by cytoplasm– responsible for phagocytosis NOT locomotion

Clade Rhizaria

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

carries the food inro the central body• B. Forams: formerly called foraminiferans

– named for their porous shells – holes are called foramen– 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 – in sand or attached to rocks or algae

• C. Cercozoans – the amoebas

LE 28-23

200 µmAxopodia

Forams

Radilarins

C. Cercozoans• contain the organisms called amoebas• amoeba species are also found in other clades• most are heterotrophs – many are parasites of plants and animals; many are

predators• predators species include the most important predators of bacteria in many

ecosystems

Clade Archaeplastida

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

• 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• divided into:• A. Red algae • B. Green algae• C. Charophytes – includes Plants

Cyanobacterium

Primaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Secondaryendosymbiosis

Heterotrophiceukaryote

Red algae

Green algae

Dinoflagellates

Plastid

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

A. Red Algae:Rhodophyta

• red algae – 6000 species– multicellular – most are autotrophic – photosynthesis– possess plastids that contain numerous pigments– red pigment = phycoerythritin and blue pigment = phycocyanin (phycobilins)

• masks the green of the chlorophyll in the plastids– 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• shallow water algae may not have as much phycoerythritin and may be more green

– sugar storage form = floridean– some can be parasitic on other red algae – lack pigmentation for photosynthesis– cell wall includes a rigid inner part of microfibrils and a matrix of proteins and

sugars– this matrix is also called agar = sulfated polymers of galactose– largest red aldae 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

B. Green algae: Chlorophyta

• green algae– named for the green chloroplasts –pigments and structure are

very similar to plants– divide into two groups:– 1. Charophytes – most closely related to plants– 2. Chlorophytes – 7000 species

• chloro = “green”• unicellular forms • unicellular forms live symbiotically with other eukaryotes –

contributing to photosynthetic output• also live symbiotically with fungus – as lichens• some are also multicellular - colonial, filamentous and sheetlike

forms• mostly freshwater• chlorophylls a and b + carotenoid pigments• sugar storage form = starch• cell walls made of cellulose

Chlorophytes

• 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 from

CO2– eyespot or stigma

» movement towards light– two small contractile vacuoles at the base of

the flagella – function as osmoregulatory organs

– sexual reproduction is also possible – cell division produces gametes of each “sex”

Chlorophytes• size and complexity of green algae has evolved one of three ways:

– 1. formation of colonies of individual cells – e.g. Volvox• colony or 500 to 60,000 cells – mostly smaller vegetative cells• individual cells resemble Chlamydomonas - biflagellated• cells are connected by thin strands of cytoplasm• flagella all beat in a coordinated fashion – rotates the colony in a clock-wise fashion• cells have eyespots – will orient toward the light• some cells reproduce asexually• other cells are reproductive - develop from the cells at the equator = called gonads• zygote undergo mitosis until they form a sphere – flagella are on the inside!! therefore it must

invert before leaving• the daughter colony remains in the parental colony until it ruptures

– 2. repeated division of nuclei with no cytoplasmic division – multinucleate filaments (pond scum)

– 3. formation of true multicellular forms by mitosis and cytokinesis

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.

Green algae: Reproduction

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 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

• sexual reproduction: upon shortage of nutrients – haploid zoospore develops into gametes – male and female– 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 biflagellated mature cells that can continue the

sexual life cycle or reproduce asexually

Clade Unikonta

• recently proposed clade• supergroup of eukaryotes that includes

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

A. Amoebozoans• lobe or tube-shaped pseudopodia rather than threadlike• 1. Gymnamoebas

– unicellular– soil, freshwater and marine– most are heterotrophic – consume bacteria and other protists plus detritus

(decomposers)– some can possess shells = tests– particle feeders – use their pseudopodia to capture food

• 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– plasmodial

• brightly pigmented – orange or yellow• named for the formation of a feeding stage = plasmodium in the life cycle• many similarities to fungus – including the formation of fruiting bodies & spores• plasmodium – very large but still is unicellular

– cell undergoes mitosis but fails to divide through cytokinesis – “super-cell”– lives on organic matter– takes up food via phagocytosis– then undergoes cytoplasmic streaming – cytoplasm streams first one way then the next – distribution of nutrients

and O2• takes on a web-like form and undergoes sexual reproduction when conditions become harsh• these bodies develop into fruiting bodies or sporangium via meiosis which are released as 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) - 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 – mitosis without cytokinesis

1 mm

MEIOSISHaploid (n)

Key

Diploid (2n)

Zygote (2n)

SYNGAMY

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Stalk

Amoeboid cells(n)

GerminatingsporeFlagellated cells

(n)

3. Mycetozoans:Plasmodial slime molds

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

• feeding stage is a solitary amoeboid form = myxoameoba– engulfs bacteria and yeasts by phagocytosis

• can undergo asexual or sexual reproduction– determined by food supply

• sexual reproduction: takes place in presence of abundant food– two halpoid amoebae fuse and form the zygote– the zygote engulfs more haploid amoebae to form a giant cell (2n)– forms a cell wall and begins to divide into numerous haploid amoebae via meiosis then mitosis– the newly formed amoebae are release when the cell wall bursts

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

pseudoplasmodium• myxoameobae secrete cAMP upon the decrease in food supply• cAMP attracts other myxoameobae – secrete more cAMP etc…. (positive feedback)

– 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– formation of the stalk requires the death and dessication of many of amoebae in the aggregation– genetic information that directs formation of a stalk cell and a spore-forming cell???– spores are released – in the presence of food – haploid myxoamoebae emerge from spores

3. Mycetozoans:Cellular slime molds