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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 Primary endosymbiosis Heterotrophic eukaryote Red algae Green algae Secondary endosymbiosis Secondary endosymbiosis Secondary endosymbiosis Plastid Dinoflagellates 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

Excavata Eukaryotic Phylogenetic Tree Chromalveolata Rhizaria Unikonta Alveolata Stramenopila Archaeplastida Amoebozoa (Opisthokonta) (Viridiplantae) Ancestral eukaryote

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 flagella LE 28-5b Flagella Undulating membrane 5 µm

Trichomonas vaginalis

, a parabasalid (colorized SEM)

•

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 trypanosome multiplication in the human host – e.g. in the blood bit by fly and transfer multiplication in the fly’s gut and then in the salivary gland

2. Euglenoids – The Euglena

– – – 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 a “

pocket

”

structure

two flagella that emerge from • 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

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 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

• • • • • • • 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

Plasmodium Life Cycle

LE 28-11 Inside mosquito Sporozoites (

) Inside human Merozoite Liver Liver cell Oocyst MEIOSIS Zygote (2

) Merozoite (

) Red blood cells Red blood cell Apex

0.5 µm

FERTILIZATION Gametes Gametocytes (

) Key Haploid (

) Diploid (2

)

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

Paramecium

LE 28-12 • • 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 FEEDING, WASTE REMOVAL, AND WATER BALANCE

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.

Thousands of cilia cover the surface of

Paramecium

50 µm

Micronucleus Contractile vacuole Macronucleus

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.

Oral groove Cell mouth 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

• 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

Paramecium

Thousands of cilia cover the surface of

Paramecium

50 µm

Micronucleus Contractile vacuole Macronucleus

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.

Oral groove Cell mouth 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

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 Compatible mates CONJUGATION AND REPRODUCTION Two cells of compatible mating strains align side by side and partially fuse.

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.

Macronucleus The cells swap one micronucleus.

MEIOSIS Diploid micronucleus Diploid micronucleus Haploid micronucleus MICRONUCLEAR FUSION 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.

Micronuclei fuse, forming a diploid micronucleus.

The cells separate.

Key Conjugation Reproduction

Paramecium

– – – – – 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

Compatible mates CONJUGATION AND REPRODUCTION Two cells of compatible mating strains align side by side and partially fuse.

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.

Macronucleus The cells swap one micronucleus.

MEIOSIS Diploid micronucleus Diploid micronucleus Haploid micronucleus MICRONUCLEAR FUSION 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.

Micronuclei fuse, forming a diploid micronucleus.

The cells separate.

Key Conjugation Reproduction

Got all that??

-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 Compatible mates CONJUGATION AND REPRODUCTION Two cells of compatible mating strains align side by side and partially fuse.

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.

Macronucleus MEIOSIS The cells swap one micronucleus.

Diploid micronucleus Diploid micronucleus Haploid micronucleus MICRONUCLEAR FUSION Two rounds of cytokinesis partition one macronucleus 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.

Micronuclei fuse, forming a diploid micronucleus.

The cells separate.

Key Conjugation Reproduction

• • • • •

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

Hairy flagellum Smooth flagellum

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

Algae: Photosynthetic Protists

• 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

Algae: Photosynthetic Protists

• 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

• • 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

Stramenophiles: 1. Oomycetes: Water molds

• • • • • • 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

water mold

•

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 Cyst Germ tube Oogonium Egg nucleus (

) Antheridial hypha with sperm nuclei (

) MEIOSIS ASEXUAL REPRODUCTION Zoospore (2

) Zoosporangium (2

) FERTILIZATION Zygote germination Zygotes SEXUAL (2

) REPRODUCTION Key Haploid (

) Diploid (2

)

•

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

fertilization tubes = fertilization

“ hook ” around the oogonium and deposit their nuclei through – – – –

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 Cyst Germ tube Oogonium Egg nucleus (

) Antheridial hypha with sperm nuclei (

) MEIOSIS ASEXUAL REPRODUCTION Zoospore (2

) FERTILIZATION Zygote germination SEXUAL REPRODUCTION Zygotes (2

) Zoosporangium (2

) Key Haploid (

) Diploid (2

)

• • • • • •

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

Brown algae Thallus

• 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

4. Brown algae: Phaeophyta

Brown algae Thallus

Brown algae: Life cycle

• 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

e.g. Laminaria

Key Haploid (

) Diploid (2

) Sporangia Sporophyte (2

) Female Zoospores Gametophytes (

) Male

An overview of Alternation of Generations

1. 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

– – – – – – – 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 Key Haploid (

) Diploid (2

) Sporangia Sporophyte (2

) Female Zoospores Gametophytes (

) Male

e.g. Laminaria

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 Radilarins Axopodia

200 µm

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 Primary endosymbiosis Heterotrophic eukaryote Plastid Red algae Plastid Green algae

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

Archaeplastida - A. Red Algae: Phylum Rhodophyta

•

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 - 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

– 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

1 µm

Flagella Cell wall Nucleus Regions of single chloroplast Zoospores ASEXUAL REPRODUCTION Mature cell (

) SEXUAL REPRODUCTION SYNGAMY Zygote (2

) MEIOSIS Key Haploid (

) Diploid (2

)

•

Green algae: Life Cycle

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

1 µm

Flagella Cell wall Nucleus Regions of single chloroplast Zoospores ASEXUAL REPRODUCTION FERTILIZATION Mature cell (

) SEXUAL REPRODUCTION Zygote (2

) MEIOSIS Key Haploid (

) Diploid (2

)

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

Unikonta: A. Amoebozoans

•

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

Plasmodial slime molds

• • • • • • • • 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

– – lives on organic matter – takes in through phagocytosis “

super-cell

” 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 Zygote (2

) FERTILIZATION Flagellated cells (

) Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Amoeboid cells (

) Germinating spore Mature sporangium Spores (

) MEIOSIS Stalk 1 mm Key Haploid (

) Diploid (2

)

Cellular slime molds

Fruiting bodies Spores (

) Emerging amoeba Solitary amoebas (feeding stage) ASEXUAL REPRODUCTION Aggregated amoebas Migrating aggregate FERTILIZATION SEXUAL Zygote (2 REPRODUCTION

) MEIOSIS Amoebas Key Haploid (

) Diploid (2

) • • • 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

200 µm 600 µm

Cellular slime molds

Sorus Fruiting bodies Spores (

) Emerging amoeba Solitary amoebas (feeding stage) ASEXUAL REPRODUCTION Aggregated amoebas Migrating aggregate SYNGAMY SEXUAL Zygote (2 REPRODUCTION

) MEIOSIS Amoebas Key Haploid (

) Diploid (2

) pseudoplasmodium pseudoplasmodium

200 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

600 µm