BI113: Lecture 12

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BI-113 Lecture 12

• Plant-like Protistans

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And now for something completely different . . .

• Different Life Cycles and their Significance to
  Eukaryotic Life
• The advent of SEX and genetic recombination as
  key to the evolution of life on Earth
• Allows for novel genetic combinations, which are
  then subject to natural selection
• Three types of meiosis
• Zygotic
• Gametic
• Sporic

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Zygotic Meiosis

• Haplontic cycle
• Formation of a zygote (2n) during some stage of
  the life cycle
• Free-living cells (organisms) are haploid (n) and
  represent the conspicuous part of the life cycle
• Haploid gametes (produced via mitosis of
  individuals) undergo fusion - syngamy - to form a
  zygote (2n)
• This undergoes meiosis to produce four new
  haploid cells (2 are male 2 are female
  -)
• Seen most commonly in algae

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Zygotic Meiosis
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Gametic Meiosis

• Diplontic cycle
• Diploid (2n) organism as major life stage
• Gametes are the only haploid cells, produced by
  meiosis
• This is what we typically think of when we
  consider sexual reproduction
• Haploid gametes (n) fuse at fertilization to
  produce a diploid zygote that undergoes
  development to produce a free-living organism (2n)

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Gametic Meiosis
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Sporic Meiosis and Alternation of Generations

• Important to the life stages and adaptations in
  many Protists
• Particularly algae (and in higher organisms, the
  plants)
• We will see this carried through as an important
  aspect of life in many organisms
• Spore-forming cells produce haploid spores (n) by
  meiosis
• Spores form a discrete life stage, the
  gametophyte, which is haploid and often a
  free-living, multicellular thallus-like structure

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Alternation of Generations

• Gametophyte produces haploid gametes (n) of
  different sexual strains
• Male gametes are often flagellated and motile
• Female gametes are large, non-motile cells
• Gametes fuse to produce a zygote, which gives
  rise to the diploid sporophyte tissue
• One feature of this mode of life is the relative
  amount of haploid tissue (gametophyte) compared
  to diploid tissue (sporophyte)
• There is an increased role for the sporophyte
  generation when looking at the phylogeny of plants

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Sporic Meiosis
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Protistan Relations
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Algae - Plant-like Protists

• Exhibit photosynthesis
• Produce much atmospheric oxygen (O2)
• Responsible for the production of nearly half (50
  ) of the organic material (biomass) in certain
  ecosystems
• Significant as primary producers in aquatic
  systems
• Important role in food webs in many ecological
  settings
• Very diverse, polyphyletic assemblage of
  unrelated taxa
• Classification based on differences in
• Photosynthetic pigments
• Type of carbohydrate storage
• Arrangement and number of flagellae

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Pyrrhophyta - Dinoflagellates

• Marine and fresh-water species
• 2,100 species
• Pigments - brown Chlorophyll a and c,
  carotenoids and xanthophylls
• Carbohydrate molecule - Starch
• Flagellae - 1 equatorial 1 polar
• Cell wall - submembranous cellulose with silica
  to form shell
• Many are luminescent
• Produce toxins which are associated with red
  tides
• Reproduction by mitotic fission
• Gonyaulax, Ceratium, Noctiluca, Pfiesteria

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Dinoflagellate Diversity
Ceratium
Spiniferites
Histiophysis
Gonyaulax
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Red tide caused by dinoflagellates
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Euglenophyta - Euglena and its relatives

• Mostly fresh-water
• 1000 species
• Pigments - Green Chlorophyll a and b,
  carotenoids and xanthophylls
• Carbohydrate molecule - Paramylon
• Flagellae - 1 to 3, in apical position
• Cell wall - No cell wall
• Instead, there is a sub-membraneous protein

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Euglenophyta
Euglena dividing
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Chrysophyta - Golden Algae

• Predominately fresh-water and colonial
• 1,000 species
• Pigments - Golden olive Chlorophyll a sometimes
  c, carotenoids and xanthophylls
• Become facultatively heterotrophic in the absence
  of adequate light
• Carbohydrate molecule - Chrysolaminarin
• Flagellae - 1 or 2, in apical position
• Cell wall - Pectic compounds with siliceous
  material
• Form cysts to survive harsh environmental
  conditions
• Freezing and desiccation

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Chrysophyta

• The fossils of chrysophytes, like those of
  diatoms, are often used as paleoecological
  indicators to reconstruct ancient environments.

Dinobryon
Synura
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Bacillariophyta (Chrysophyta) - Diatoms

• Fresh-water and marine forms
• 11,500 species
• Pigments - Olive brown Chlorophyll a and c,
  carotenoids and xanthophylls
• Carbohydrate molecule - Leucosin and
  chrysolaminarin
• Flagellae - 1, only in sperm
• Cell wall - hydrated silica in an organic matrix
  (opaline silica)
• Organisms are enclosed in a siliceous test
• Made of two halves that fit together like a petri
  dish
• These are variously ornamented with pores
• Significant contribution to oceanic sediments
• Characteristic species and assemblages used in
  determining the age of certain rock strata

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Diatom Diversity
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Rhodophyta - Red Algae

• Mostly marine, some fresh-water - many found in
  tropical waters
• Occur at the deepest ocean depths (pigments
  utilize blue wavelengths that penetrate further)
• 4,000 species
• Pigments - Red to Black Chlorophyll a,
  carotenoids, phycobilins, chlorophyll d
• Carbohydrate molecule - Floridean starch
• Flagellae - none
• Cell wall - Cellulose matrix with other
  polysaccharides
• Some with CaCO3 impregnated in cell walls
• Hard, coralline forms

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Rhodophyta
Chondrus crispus - Irish moss, a red alga used by
brewers
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Phaeophyta - Brown Algae

• Almost exclusively marine (many found in cold
  oceanic waters)
• 1,500 species
• Pigments - Olive brown Chlorophyll a and c,
  carotenoids and xanthophylls
• Carbohydrate molecule - Laminarin
• Flagellae - 2, lateral, in sperm only
• Cell wall - Cellulose matrix with a variety of
  polysaccharides
• Sargassum

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Phaeophyta Diversity
Kelp
Fucus sp. (above) - a common marine species with
typical, gas-filled Sargassum sp. (right) - a
warm-water brown alga that is free floating.
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Chlorophyta - Green Algae

• Mostly fresh-water, but some marine forms
• 7,000 species
• Pigments - Green Chlorophyll a and b, and
  carotenoids
• Carbohydrate molecule - Starch (like plants)
• Flagellae - 2 or more, apical or subapical
• Cell wall - Cellulose (also like plants)
• Agar, used in bacteria media and electrophoretic
  gels
• Carrageenin (gelatinous) used in ice cream,
  paints, cosmetics etc.
• Great variety in forms
• Single-celled - Chlamydomonas
• Multi-cellular - Ulva and Spirogyra
• Colonial - Volvox

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Chlorophyta
Spirogyra conjugating
Spirogyra - a common freshwater green alga
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Chlamydomonas Life Cycle
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Volvox
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Ulva Life Cycle