BSCI 124 - SECTION 2001

Department of Cell Biology & Molecular Genetics

Algae and Spore forming plants
Plant Diversity: Evolution of Life Cycles

    I. Kingdom Protista: The Algae
        · Eukaryotic unicellular and simple multicellular organisms
        · photoautotrophs; photosynthetic pigments – primarily chl a, b, and/or c.  Also accessory pigments.
        · phytoplankton versus seaweeds (the body of a seaweed is called a thallus; there are no roots, stems, or leaves).
        · requires a wet or very moist environment to exist and reproduce (algae have motile male gametes and single celled sex organs)
        · Reproduction: asexually or sexually (alternation of generations: haploid, gamete-producing generation called the gametophyte and a diploid, spore-producing generation called the sporophyte.  Spores
            released from the sporophyte develop into gametophytes).

        Types of Algae:
        A. Diatoms
                1. unicellular; primarily asexual reproduction
                2. are components of cold freshwater and marine phytoplankton: base of the marine food chain
                3. photosynthetic pigments: Chl a, c, carotenoids and xanthophylls.  The cell walls contain silica (glass)
                4. Commercial uses: diatomaceous earth.

        B. Red Algae
                1. multicellular seaweeds.  All red algae reproduce sexually
                2. warm, tropical, marine inhabitants; deep waters.  Play a significant role in coral reefs.
                3. Chl a, carotenoids, phycoerythrin (a red accessory pigment)
                4. Cell walls are cellulose, agar & carageenan. Coral reef red algae have calcium carbonate and magnesium carbonate cell walls.
                5. Commercial uses: various

        C. Brown algae
                1. all are multicellular seaweeds and marine inhabitants of cool shallow waters.  Sexual and asexual reproduction.
                2. Chl a, c, and the brown carotenoid pigment: fucoxanthin. Cell walls made of cellulose and algin.
                3. Fucus, Laminaria, and giant kelp (Macrocystis sp.)
                4. Commercial uses: various

        D. Dinoflagellates
                1. phytoplankton: base of the marine food chain.  Mainly unicellular; mostly asexual reproduction
                2. Chl a, Chl c, and a mix of carotenoids
                3. generally a cellulose cell wall
                4. red tides by explosive growth (called blooms) in warm coastal waters; bioluminescent forms; and Pfiesteria toxin
                5. No commercial value

        E. Green algae
                1. chloroplasts are very similar in structure & pigment composition to chloroplasts in plants. Cellulose cell walls like plants.
                2. predominantly freshwater, some marine
                3. both sexual and asexual reproduction
                4. many body forms: unicellular types, colonial forms, multicellular thallus (‘leafy’) forms are seaweeds
                5. can live in symbiosis with fungi = lichens
                6. Commercial uses: various

    II.  The Plant Kingdom
        A. Prior to 430 million years ago, life only in oceans.
        B. Characteristics land plants share with their green algal ancestors
        C. What are the challenges/adaptations associated with life on land?
        D. All land plants have a sexual reproductive life cycle (alternation of generations):
                1. haploid (1n) gametophyte and diploid (2n) sporophyte generations
                2. sporophyte is larger and more noticeable than the gametophyte in all land plants EXCEPT the Bryophytes.
        E. Non-Vascular Land Plants (Bryophytes)
                1. Primitive Land Plants: Spore formers (mosses, liverworts, & hornworts).  Example: Marchantia, a liverwort you saw in lab
                    a) They dwell on land, but they have NO vascular system (rhizoids to anchor only); they are restricted to wet environment; have pores on the thallus surface, NOT stomata.
                    b) Life cycle: is water dependent reproduction (motile sperm swim to the egg for fertilization).
                    c) 1n gametophyte has archegonium (female structures) and antheridium (male structures).
                    d) 1n gametophyte spore is the dominant phase.  2n sporophytes are only present for a short time after fertilization.
        F. Vascular Land Plants
                1. Ferns are seedless vascular plants.  Better adapted to life on land: leaves (called fronds) have true stomata.
                2. Life cycle: is still water dependent  (motile sperm swim to egg for fertilization).
                    a) Reproductive structures are on the underside of the leaf; are sporangia arranged in clusters called Sori.
                        (1) Meiosis in sporangium produces 1n spores (are homosporous).  Spores germinate to produce a ‘heart shaped’ 1n gametophyte.
                        (2) 1n gametophyte has archegonium (female structures) and antheridium (male structures).
                        (3) Fertilized zygote (2n) in archegonium develops into a sporophyte.  The 2n sporophyte is larger and more dominant than 1n gametophyte.  There are NO seeds!



Classification of Plants:

                                                                                          # of Extant Species
I. Non vascular Land Plants (Bryophytes):
                 Mosses                                                                  12, 000
                 Liverworts                                                               6, 500
                 Hornworts                                                                   100

II. Vascular Land Plants:
        A. Seedless vascular plants:
                 Lycophytes                                                             1, 000
                 Horsetails                                                                       15
                 Ferns                                                                       12, 000

        B. Advanced Vascular Seed Plants:
                  Conifers                                                                        550
                  Cycads                                                                         100
                  Gingko                                                                              1
                  Gnetae                                                                            70

                   Flowering plants                                                   250, 000

Additional sites of interest:
protists: excellent pictures