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Division: Chlorophyta – Green Algae Very Important from an Evolutionary Division: Chlorophyta – Green Algae Very important from an evolutionary point of view Some formed complex multicellular bodies Moved onto land – later to become “true” plants • Body Construction in the Green Algae – simplest is a motile unicellular organism – from this simple plan several paths were taken – Motile colonies • Cells adhere to one another • All cells are similar 17 Division: Chlorophyta – Green Algae – Nonmotile Colonies • Cells either never develop flagella or flagella is lost • Flagella considered the ancestral trait – Filamentous Body • Cells held together via middle lamella • Cell division transverse; if longitudinal results in filament branching • Parts can be specialized » Holdfast » Gamete production 18 Division: Chlorophyta – Green Algae • Membranous Body – Cell division occurs in only two planes • Forms a thin sheet of cells • Easily torn by wave action • Parenchymatous Body – Cell division occurs in three planes • Cells connected by plasmodesmata • True parenchyma tissue is formed 19 Division: Chlorophyta – Green Algae • Coenocytic or Siphonous Body – Karyokinesis without cytokinesis; results in a giant multinucleate cell 20 Life Cycles of the Green Algae • Asexual Reproduction – ex. Euglenoids – Cell cycle – mitosis and cytokinesis • Sexual Reproduction – Requires meiosis – Requires syngamy – Simplest form • Dipoloid cell undergoes meiosis – Haploid individuals produced that can reproduce via mitosis – Some cells act as gametes and fuse » Produces a diploid cell that can reproduce via mitosis • Very little difference between diploid and haploid individuals • Referred to as being DIBIONTIC (alternation of generations between haploid and diploid) 21 Life Cycles of the Green Algae – Monobiontic Species - Only one free-living generation • Example #1 – Haploid phase only represented by the individual » Can be either uni or multicellular » Carries out photosynthesis and growth – Only diploid cell is the zygote 22 Life Cycles of the Green Algae • Example #2 – Diploid phase represents the individual - undergoes vegetative growth – Haploid cells are gametes which undergo syngamy 23 Life Cycles of the Green Algae • Isomorphic vs Heteromorphic Generations 24 Life Cycles of the Green Algae • Gamete Development – Early on gametes were identical, isogamous – Later anisogamy developed (slight difference) – Ultimately oogamy evolved 25 Representative Genera of the Green Algae • Unicellular Species – ex. Chlamydomonas – Chlorophylls a and b, carotenoids, xanthophylls – Starch produced in chloroplasts – Two anterior flagella (common to most motile green algae) – Reproduces via mitosis, meiosis + syngamy • Haploid resorbs flagella • Divides mitotically producing either 2, 4, 8, or 16 cells • Each new cell grows a two flagella • These cells swim and eventually meet another cell – Plasmogamy and karyogamy produce a single large zygote (only diploid cell) – Becomes dormant – Germinates via meiosis, producing four haploid individuals 26 Representative Genera of the Green Algae • Motile Colonial Species – cell closely resemble Chlamydomonas – after zygote divides individuals are held together by a gelatinous mass 27 Representative Genera of the Green Algae – Based upon advances • Gonium – Colonies small (4 – 32 cells) – Simple organization, flagella beat in synchrony 28 Representative Genera of the Green Algae • Pandorina – Similar in size to Gonium – Some differentiation, anterior cells slightly different than posterior cells, causes colony to swim in one direction 29 Representative Genera of the Green Algae • Volvox – up to 50,000 cells (can see colony without a microscope) – Group of anterior cells, about 50, modified for reproduction 30 Representative Genera of the Green Algae • Filamentous Species – Ulothrix • Monobiontic • A single row of cells, with terminal cell modified to a holdfast • Zoospores can be produced mitotically – Possess four flagella – Settle to bottom – Germinate into new filaments • Some cells produce gametes – isogamous – Two flagella, resemble Chlamydomonas – Fuse producing a zygote which germinates via meiosis producing haploid zoospores – Settle to the bottom and germinate into a filament 31 Representative Genera of the Green Algae – Syrogyra • Very common if freshwater environments • Chloroplast spirally arranged • No swimming gametes; rather a conjugation tube • Each filament is haploid (+ or -) • Zygote becomes dormant and thick walled • Germinates into a new filament from haploid spores 32 Representative Genera of the Green Algae • Laminar Species – Ulva • Similar to Ulothrix • Cell germinate in two planes • Dibiontic life cycle (alternation of isomorphic generations) • Separate individuals producing different gametes, dioecy 33 Representative Genera of the Green Algae • Coenocytic Species – Dibiontic life cycle – Heteromorphic generations (initially caused real problems) 34 Representative Genera of the Green Algae • Parcnchmatous Species – some types divide via a phragmoplast (plants do this) possibly ancestral – Chara – has multicellular gametangia (plant or not) 35 Division Phaeophyta: Brown Algae • Major Characteristics – Mostly marine, in littoral zone (between high and low tides) – Very complex anatomically and morphologically – Similar to plants but very different • Possess chlorophylls a and c, fucoxanthin, violaxanthin, diatoxanthin and carotenes (implications?) • Storage product is laminarin (glucose polymer), mannitol and fat (no starch) • Have a holdfast, stipe (stalk) and a blade 36 Division Phaeophyta: Brown Algae • Cell walls contain cellulose and alginic acid (used in paint an food industry) • Can be very large, and have developed specialized regions – Holdfast, anchoring – Epidermis to prevent damage from waves – With an epidermis diffusion is impaired, need a conducting system » Have trumpet cells that resemble phloem (convergence) 37 Division Phaeophyta Brown Algae – Ectocarpus • Isomorphic generations • Diploid sporophytes possess unilocular sporangia at the ends of small terminal branches – First nuclear division is via meiosis (haploid) – Zoospores germinate into gametophyte » Ends of branches are gametangia » Plurilocular gametangia » Gametes anisogamous » Settle to the bottom secrete ectocarpene, attracts opposite, syngamy ensues 38 Division Phaeophyta Brown Algae – Fucus • Common on rocks of intertidal zone • Diploid individuals seen at low tide • Dichotomously branched blades • Ends of branches posses receptacles that contain concepticles 39 40 Division Rhodophyta: Red Algae • Major Characteristics – Large group – 3,900 sp. – Very different from other algae and true plants • Like cyanobacteria have phycobilin (accessory pigment) • Typically red (phycoerythrin) can be purple, brown or black (phycocyanin), chlorophyll a and carotenoids • Storage product floridean starch, similar to glycogen • Different sugars formed • Cell wall contains cellulose and sulfated galactans (slimy mucilages) – used to produce agar • No plasmodesmata • Mostly multicellular • Life cycles poorly known – Unique, lack any motile cells – Lack centrioles but have polar rings for this function – Polysiphonia – three phases to its life history » Haploid gametophyte » Diploid carposporophyte » Diploid tetrasporophyte 41 42.
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