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Chapter 28: the Protists

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Title: Chapter 28: the Protists


1
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

2
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 doesnt 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

3
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

4
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

5
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

6
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

7
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

8
Eukaryotic Phylogenetic Tree
Fungi
Plantae
Charophyta
9
Clade Excavata
  • A. Diplomonads
  • B. Parabasilids
  • C. Euglenozoans

10
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

11
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

12
  • B. Parabasalids
  • also have reduced/modified mitochondria
    hydrogenosomes
  • include the protists called trichomonads
    Trichomonas vaginalis
  • mobility through an undulating membrane in
    addition to flagella

13
  • 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

14
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

15
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
  • fly injects the trypanosome
  • multiplication in the human host e.g. in the
    blood
  • bit by fly and transfer
  • multiplication in the flys gut and then in the
    salivary gland

16
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 - 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

used to be classified as the Class
Phytomastigophorea
17
2. Euglenoids
  • 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

used to be classified as the Class
Phytomastigophorea
18
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

19
Clade Chromalveolata
  • A. Alveolates
  • 1. Dinoflagellates
  • 2. Apicomplexans
  • 3. Ciliates
  • B. Stramenophiles
  • 1. Diatoms
  • 2. Golden Algae
  • 3. Brown Algae
  • 4. Oomycetes

20
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

21
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

22
  • 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

23
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

24
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

25
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 mosquitos digestive tract
  • the fertilized cell zygote
  • 7. an oocyst develops from the zygote and adheres
    to the wall of the mosquitos gut
  • produces more sporozoites
  • these are delivered to a new human host when the
    mosquito bites another human

26
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

27
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

28
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

29
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

30
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

31
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
32
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

33
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)

34
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

35
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

36
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)

37
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
38
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
39
  • 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

40
  • 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

41
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

42
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

43
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
44
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

Brown algae Thallus
45
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

Brown algae Thallus
46
Brown algae Life cycle
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 Generations
  • the spores develop into gametophytes (n)
  • the gametophytes make gametes (n)
  • the gametes fuse and regenerate the diploid
    sporophyte (2n)

47
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

e.g. Laminaria
48
Clade Rhizaria
  • characterized by the presence of threadlike
    pseudopodia extensions of the cytoplasm that
    bulge anywhere along the cells 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

49
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

50
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

Radilarins
51
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
52
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

53
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

54
Clade Archaeplastida
  • Archaeplastida can be divided into
  • A. Red algae Phylum Rhodophyta
  • B. Green algae Phylum Chlorophyta
  • C. Charophytes includes Plants Phylum
    Charophyta

55
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

56
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

57
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

58
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

59
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

60
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

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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

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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.
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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

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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

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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

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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 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

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Cellular slime molds
  • 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

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Cellular slime molds
  • 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
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