29 C1 Bryophytes

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29 C1 Bryophytes

  1. 1. CHAPTER 29 PLANT DIVERSITY I: HOW PLANTS COLONIZED LAND Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section C1: Bryophytes 1. The three phyla of bryophytes are mosses, liverworts, and hornworts 2. The gametophyte is the dominant generation in the life cycles of bryophytes
  2. 2. <ul><li>Bryophytes are represented by three phyla: </li></ul><ul><ul><li>phylum Hepatophyta - liverworts </li></ul></ul><ul><ul><li>phylum Anthocerophyta - hornworts </li></ul></ul><ul><ul><li>phylum Bryophyta - mosses </li></ul></ul><ul><li>Note, the name Bryophyta refers only to one phylum, but the informal term bryophyte refers to all nonvascular plants. </li></ul>1. The three phyla of bryophytes are mosses, liverworts, and hornworts Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.15
  3. 3. <ul><li>The diverse bryophytes are not a monophyletic group. </li></ul><ul><ul><li>Several lines of evidence indicate that these three phyla diverged independently early in plant evolution, before the origin of vascular plants. </li></ul></ul><ul><li>Liverworts and hornworts may be the most reasonable models of what early plants were like. </li></ul><ul><li>Mosses are the bryophytes most closely related to vascular plants. </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  4. 4. <ul><li>In bryophytes, gametophytes are the most conspicuous, dominant phase of the life cycle. </li></ul><ul><ul><li>Sporophytes are smaller and present only part of the time. </li></ul></ul><ul><li>Bryophyte spores germinate in favorable habitats and grow into gametophytes by mitosis. </li></ul><ul><li>The gametophyte is a mass of green, branched, one-cell-thick filaments, called a protonema . </li></ul>2. The gametophyte is the dominant generation in the life cycles of bryophytes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  5. 5. <ul><li>When sufficient resources are available, a protonema produces meristems. </li></ul><ul><li>These meristems generate gamete- producing structures, the gametophores . </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.16
  6. 6. <ul><li>Bryophytes are anchored by tubular cells or filaments of cells, called rhizoids . </li></ul><ul><ul><li>Rhizoids are not composed of tissues. </li></ul></ul><ul><ul><li>They lack specialized conducting cells. </li></ul></ul><ul><ul><li>They do not play a primary role in water and mineral absorption. </li></ul></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  7. 7. <ul><li>Bryophyte gametophytes are generally only one or a few cells thick, placing all cells close to water and dissolved minerals. </li></ul><ul><li>Most bryophytes lack conducting tissues to distribute water and organic compounds within the gametophyte. </li></ul><ul><ul><li>Those with specialized conducting tissues lack the lignin coating found in the xylem of vascular plants. </li></ul></ul><ul><li>Lacking support tissues, most bryophytes are only a few centimeters tall. </li></ul><ul><li>They are anchored by tubular cells or filaments of cells, called rhizoids . </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  8. 8. <ul><li>The gametophytes of hornworts and some liverworts are flattened and grow close to the ground. </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.15a, b, c
  9. 9. <ul><li>The gametophytes of mosses and some liverworts are more “leafy” because they have stemlike structures that bear leaflike appendages. </li></ul><ul><ul><li>They are not true stems or leaves because they lack lignin-coated vascular cells. </li></ul></ul><ul><li>The “leaves” of most mosses lack a cuticle and are only once cell thick, features that enhance water and mineral absorption from the moist environment. </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  10. 10. <ul><li>Some mosses have more complex “leaves” with ridges to enhance absorption of sunlight. </li></ul><ul><ul><li>These ridges are coated with cuticle. </li></ul></ul><ul><li>Some mosses have conducting tissues in their stems and can grow as tall as 2m. </li></ul><ul><ul><li>It is not clear if these conducting tissues in mosses are analogous or homologous to the xylem and phloem of vascular plants. </li></ul></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.15d
  11. 11. <ul><li>The mature gametophores of bryophytes produce gametes in gametangia. </li></ul><ul><ul><li>Each vase-shaped archegonium produces a single egg. </li></ul></ul><ul><ul><li>Elongate antheridia produce many flagellated sperm. </li></ul></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 29.16
  12. 12. <ul><li>When plants are coated with a thin film of water, sperm swim toward the archegonia, drawn by chemical attractants. </li></ul><ul><ul><li>They swim into the archegonia and fertilize the eggs. </li></ul></ul><ul><li>The zygotes and young sporophytes are retained and nourished by the parent gametophyte. </li></ul><ul><ul><li>Layers of placental nutritive cells transport materials from parent to embryos. </li></ul></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

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