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Algae and Lower Plants

  1. Kingdom Chromista - aquatic uni-or multicellular photosynthetic organisms
    1. Phylum Ochrista - chloroplasts have 3 membranes and degenerate nucleus indicating recent endosymbiosis
      1. brown algae
        1. have chlorophyll a and c
        2. unicellular or colonial, usually asexual
        3. can grow up to 40 m, giant kelp in pacific, sargassum weed
      2. diatoms
        1. silica shells
        2. ordinarily diploid
        3. dominant component of marine plankton
        4. form diatomaceous earth (pool filters)
      3. Exhibit alternation of generations - i.e. haploid - diploid
        1. isomorphic - haploid organism looks like diploid organism, e.g. Fucus
        2. larger bodied organisms reduce haploid stage, increase diploid stage
        3. meiosis often precedes a change in the environment (season or other)
    2. Phyla Haptophyta and Cryptista
      1. Haptophyta - unicellular marine algae
        1. paired flagella and a haptoneme holdfast
        2. form calcium carbonate shells when sessile
      2. Cryptista - unicellular freshwater algae with paired flagella, photosynthetic and heterotrophs
  2. Kingdom Plantae - 2 membrane chloroplasts which are free in the cytoplasm
    1. Phylum Rhodophyta - red algae, marine seaweeds
      1. floridean starch stored in cytosol - used to make agar
      2. chlorophyll a + red pigments
      3. gametes lack flagella
    2. Phylum Chlorophyta - green algae
      1. Volvicines provide an example of evolution of multicellular organisms
        1. Chlamydomonas - unicellular, aquatic biflagellate
          1. isogamous
          2. zygote is only diploid stage
        2. Gonium - 4-32 chlamy-like cells/colony in mucilagenous matrix
        3. Pandorina - 4-32 cells,
          1. show division of labor, vegetative and reproductive cells
          2. anisogamous - although gametes of both sexes are free swimming with flagella
        4. Eudorina - 16-32 cells/ colony
          1. has oogamy - female gametes remain attached to colony
        5. Pleodorina - 32-128 cells/colony - also oogamous
        6. Volvox - 500-50,000 cells/ colony
          1. oogamous
          2. some species are dioecious - separate sexes in separate colonies
      2. Some green algae are multicellular and exhibit alternation of generations, with a haploid multicellular stage
        1. sporangium is diploid and produces haploid spores as meiotic products
        2. gametophyte is haploid and produces gametes
        3. gametes fuse to form new sporangium
      3. Other green algae have multicellular haploid and diploid stage (Ulva - sea lettuce)
    3. Bryophyta - flagellated sperm must swim to eggs, therefore confined to moist habitats
      1. Mosses - green part is gametophyte, stalk is sporophyte
      2. Liverworts - reproduce asexually be gemmae buds, or by production of haploid spores
  1. Tracheophyta
    1. Key characters
      1. protective layer of cells around the reproductive organs
      2. multicellular embryos in the archegonia
      3. plumbing system in the sporphyte stage
      4. cuticles on aerial parts
    2. Psilopsida - simple, branching plant without roots. Found in Silurian, 395 MYA
    3. Lycopsida (club mosses) - early Devonian, have roots
      1. some are heterosporous - separate sexes in gametophyte generation
      2. some are homosporous (Lycopodium)
    4. Sphenopsida (horsetails) - late Devonian, common in Carboniferous
      1. have jointed hollow stems, similar to bamboo, with whorls of leaves at joints
      2. homosporous. gametophytes have antheridia and archegonia
    5. Pteropsida (ferns) - Devonian, common in Carboniferous
      1. haploid gametophyte is tiny, heart-shaped structure
      2. flagellated sperm move from antheridia to archegonia to create zygote - need water
      3. large, common plant is the diploid sporophyte
    6. Spermopsida (all seed plants) - have many adaptations for living in dry environments