Protists: The Algae

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Protists The Algae

• Autotrophic protists

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• General Characteristics of Algae. . .
• Diverse group
• Mostly photosynthetic
• Range in size from single-celled to large,
  multicellular seaweeds (marine algae do 30-40 of
  all photosynthesis on Earth)
• Must be in a damp environment when actively
  growing (lack a cuticle)
• Gametangia are formed from single cells
• Possess chlorophyll a, carotenoids, and several
  other pigments

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Phylum Dinoflagellata (Pyrrophyta)

• Algae with two flagella

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• General characteristics of Dinoflagellates. . .
• Most are unicellular some are colonial
• Some are covered with a shell of interlocking
  cellulose plates, some containing silicates
• Each has two flagella
• Some are bioluminescent
• Most are photosynthetic
• Energy storage products are usually oils or
  polysaccharides
• Many are endosymbionts (living in jellyfish,
  corals, mollusks)
• Lack a cellulose plates and flagella, and are
  called zooxanthellae
• Photosynthesize and provide food to mutualistic
  partner
• Some are parasitic

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• More about Dinoflagellates. . .
• Their reproduction is primarily asexual
• Their nucleus is unusual - they have no close
  relatives and some scientists consider
  reclassifying them
• The chromosomes are permanently condensed and
  always evident
• The nuclear membrane remains intact during
  mitosis and meiosis
• The spindles are located outside the nucleus
• Chromosomes do not make contact with spindle
  microtubules

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Most dinoflagellates are marine organisms and
they make up an important group of producers in
the marine environment.
Some species have occasional blooms (population
explosions) such as red tides Some species that
form red tides produce a toxin that leads to
massive fish kills Others are eaten by mollusks,
making them poisonous to humans
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Phylum Bacillariophyta (Chrysophyta)

• The Diatoms

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• Characteristics of Bacillariophyta (Diatoms). . .
• Most are unicellular some are colonial
• The cell walls are composed of two halves that
  overlap where they fit together (petri dish
  arrangement of shells)
• Cell walls are impregnated with silica
• There are two groups those with radial symmetry
  and those with bilateral symmetry
• Most float those that grow on surfaces move by
  gliding
• Most are photosynthetic
• Food reserves are stored as oils or carbohydrates
• They are MAJOR PRODUCERS!
• Found in fresh and ocean water, especially cooler
  marine waters
• Upon death, they sink to the ocean floor and
  become sedimentary rock

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• Diatoms reproduce primarily asexually. .
• The two halves of the cell fit together like a
  petri dish
• The cell separates into its two halves, and each
  half becomes the larger half for a new cell
• Some cells get smaller every generation
• When a fraction of the original size, sexual
  reproduction occurs
• Gametes shed the cells walls and fuse to form a
  zygote which grows a great deal before forming a
  new shell
• This restores the diatom to its original size and
  the process starts over again.

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Phylum Euglenophyta

• The euglenoids

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• Characteristics of Euglena. . .
• All are unicellular flagellates
• Most have two flagella - one long external, and
  one short internal
• Their shape continually changes their covering
  is a proteinaceous pellicle
• Reproduce only asexually
• Many photosynthesize some are heterotrophic
  (some can do both- depending on conditions)
• Most live in fresh water rich in organic material
• Used as indicators of pollution

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Phylum Chlorophyta

• The green algae

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• General characteristics of Chlorophyta. . .
• Their body forms are very diverse
• Most are flagellated during part of their life
  history
• Biochemically they are very uniform (contain
  chlorophylls a and c and carotenoids)

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• Chlorophyta are related to plants
• All are photosynthetic
• Food is stored as starch
• Most have cell walls with cellulose
• Many are symbionts (with fungi) - Lichens
• It is believe that plants evolved from green,
  algal-like ancestors
• Some are aquatic some are terrestrial
• Important producers in freshwater habitats
• These are all characteristics of plants

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• Reproduction is varied in Chlorophyta
• Asexual reproduction may involve fragmentation,
  mitotic fission or Zoospores
• Sexual reproduction may be quite complex
• Isogamous reproduction (identical flagellates
  gametes)
• Anisogamous reproduction(flagellated gametes of
  different sizes)
• Oogamous reproduction (a nonmotile egg and a
  flagellates male gamete
• Conjugation (formation of a tube and exchange of
  genetic information)

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Isogametes in Chlamydomonas
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Conjugation in Spirogyra
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Kingdom Protista - The Algae

• Rhodophyta - the red algae

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• General characteristics of Rhodophyta. . .
• Most species are multicellular often with
  interwoven fibers forming filaments which are
  delicate and feathering
• A few species are unicellular
• Most attach to substrates with rootlike holdfasts
• All are photosynthetic - they contain
  phycoerythrin (red) and phycocyanin (blue)
  pigments plus chlorophyll a and caratenoids
• Food is stored as floridean starch (carbohydrate
  similar to glycogen)
• It is believed that cyanobacteria endosymbionts
  evolved into chloroplasts in red algae
• There are no flagellated cells at any time
• They live primarily in warm tropical oceans
• Some incorporate calcium carbonate into their
  cell walls, making them very important in coral
  reef formation

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• More information for Rhodophyta. . .
• Their reproduction is complex involving an
  alternation of sexual and asexual generations
• The cell walls contain mucilaginous
  polysaccharides that have commercial value
• Agar - used in baking and as a culture medium
• Carageenan - used to stabilize emulsions in foods
  and other products (puddings, laxatives,
  toothpastes)
• Rhodophyta serves as a human food

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Phylum Phaeophyta

• The brown algae

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• General characteristics of Phaeophyta. . .
• All are multicellular, ranging in size from
  several centimeters to approximately 60 meters in
  length
• Body forms vary
• Kelps, the largest brown algae, are tough and
  leathery and have considerable differentiation
  (they have leaf-like blades, and stem-like
  stipes, and holdfasts - these are not homologous
  to leaves, stems and roots - rather they show
  convergent evolution)
• Many have gas-filled floats to increase buoyancy
• All are photosynthetic (contain chlorophyll a and
  c and cartenoids, fucoxanthin is a yellow-brown
  pigment unique to brown algae, diatoms and
  dinoflagellates)
• Food is stored as laminarin (a carbohydrate)

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• More information about Phaeophyta. .
• They are common in cooler marine waters
• Kelp forms extensive underwater forests
• It is essential as the primary food producer!
• Kelp beds are important in underwater ecology
  they form habitats for many organisms

• Brown algae are important commercially
• Algin is a polysaccharide in their cell walls
  that is used in ice cream, marshmallows, and
  cosmetics
• It is an important source of human food (oriental
  food)
• It is a rich source of minerals, especially iodine

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Reproduction in brown algae is varied and
complex They reproduce sexually with flagellated
reproductive cells - zoospores and gametes Most
have alternation of generations
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All n
2n
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Kingdom Protista

• The fungal-like Protists

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• General characteristics of the fungal-like
  Protists.
• They resemble fungi in that
• They are nonphotosynthetic
• The body is often a threadlike hyphae

• They are not fungi because
• Many produce flagellated cells
• They have centrioles
• Many produce cellulose as a major component of
  their cell walls

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Phylum Myxomycota

• The plasmodial slime molds

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• General characteristics of Myxomycota. . .
• The feeding stage is unusual - a brightly colored
  mass of cytoplasm (a plasmodium)
• The plasmodium contains many nuclei (usually
  diploid), but it is not divided into separate
  cells
• It streams over damp, decaying logs and leaf
  letter, ingesting bacteria, yeasts, spores, and
  decaying organic matter as it goes

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• Reproduction in Myxomycota. . .
• When food or moisture are insufficient, the
  plasmodium crawls to an exposed surface and
  initiates reproduction
• Stalked structures (sporangia) form
• Cell walls form around each nucleus
• Meiosis occurs, forming haploid spores
• When conditions are favorable, spores open, and a
  haploid reproductive cell emerges from each
• It is either a one-celled biflagellate or an
  amoeboid cell, depending on how wet it is
• These two forms act as gametes, eventually fusing
• The diploid zygote divides by mitosis without
  cytoplasmic division to form a multinucleate
  plasmodium

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Phylum Acrasiomycota

• The cellular
• slime molds

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• During the vegetative stage,individual amoeboid
  cells behave as separate, solitary organisms
• Each cell has a haploid nucleus
• When food or moisture become inadequate, the
  cells aggregate by the hundreds of thousands for
  asexual reproduction
• During this stage, they creep about as one unit,
  a pseudoplasmodium (slug)
• Each cell has a plasma membrane and individual
  identity
• Eventually the slug settles and forms a stalked
  structure
• Spores differentiate in a rounded structure at
  the tip
• Each spore may grow into an individual amoeboid
  cell, and the cycle repeats
• No flagellated stages sexual reproduction has
  been observed occasionally

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Acrasiomycota life cycle
All n
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Phylum Oomycota

• The water molds

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• Characteristics of Oomycota. . .
• The body (mycelium) grows over a substrate,
  digesting it and then absorbing the predigested
  nutrients
• Thread-like hyphae that make up the vegetative
  mycelium are coenocytic the body is one giant
  multinucleated cell
• The cell walls are composed of cellulose or
  chitin or both
• They reproduce asexually when conditions are good
• Reproduce sexually when conditions are poor
• They overwinter as dormant oospores
• It was a water mold that caused the famous potato
  famine of the 19th century (caused social
  upheaval and migration to U.S. and other
  countries)

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Evolution and the Protists
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• Protists are considered to be the first
  eukaryotic cells
• They may have originated 1.5 to 2 billion years
  ago
• Evidence suggests that several organelles arose
  from endosymbiotic relationships between various
  prokaryotes
• Photosynthetic bacteria may have give rise to
  chloroplasts
• Aerobic bacteria may have given rise to the
  mitochondria
• The presence of a double membrane, DNA, and
  ribosomes supports this view
• Further evidence is the fact that these
  organelles divide independently of the nucleus

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• Multicellularity arose in the Protist Kingdom,
  apparently independently several times
• An ancient organism like Prochloron may have
  given rise to chloroplasts in green algae and/or
  euglenoids
• The cyanobacteria may have given rise to the red
  algae
• An organism similar to Heliobacterium may have
  given rise to the brown algae and diatoms
• Flagellates are the most primitive Protists
• Amoeboid protozoa evolved from flagellates
• Sporozoa may have originated from flagellates
• Origin of ciliates is less certain

It is believe that green algae gave rise to the
plants Choanoflagellates or some other
flagellate gave rise to the animals and perhaps
the red algae gave rise to the fungus (unsure).