The Move to Land and Plant Diversity

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The Move to Land and Plant Diversity
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Introduction

• More than 280,000 species of plants inhabit Earth
  today.
• Most plants live in terrestrial environments,
  including deserts, grasslands, and forests.
• Some species, such as sea grasses, have returned
  to aquatic habitats.
• Land plants (including the sea grasses) are
  thought to have evolved from a certain green
  algae, called charophyceans.

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What You Need to Live On Land
Its getting hot in here!!!

• Supporting Mechanisms (vascular tissues and
  lignin)
• Absorptive structures (above and below ground)
• Conducting tissues (Vascular tissues)
• Anti-desiccation Adaptations for Body of plant
  and Gametes (cuticle and sporopollenin)
• Airborne gamete dispersal

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General Characteristics

• There are four main groups of land plants Mosses
  (bryophytes), Ferns (pteridophytes), Conifers
  (gymnosperms), and Flowering plants
  (angiosperms).
• Multicellular, eukaryotic, photosynthetic
  autotroph.
• Cell wall of cellulose, storage polysaccharide as
  starch.
• Chlorophyll a, b, and carotenoids.
• Secrete cuticle to reduce desiccation.
• Most have stomata for gas exchange (except
  Liverwort)
• Most have seed embryo with food and protective
  covering.
• Most have vascular tissues for bulk transport of
  water and nutrients. Plasmodesmata for transport
  between cells.

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Non-vascular
aka. Traecheophytes
Naked Seeded Plants
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PlantsA Monophyletic Taxon!
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The Proposed Ancestors of Land Plants

• Land plants share two key ultrastructural
  features with their closet relatives, the algal
  group called charophyceans.

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Charophyceans are the green algae most closely
related to land plants

• Homologous Chloroplasts. DNA sequences similar,
  pigments and structure similar.
• Homologous Cell Walls. Formed in similar manner
  with similar amounts of cellulose. Rosette
  cellulose-synthesizing complex.
• Homologous Sperm. Some plants have flagellated
  sperm similar to that of charophyceans.
• Perioxysomes. Help to reduce effects of
  photorespiration.
• Molecular systematics. Similar nuclear and
  chloroplast genes.
• Phragmoplasts.
• an alignment of microtubules and Golgi-derived
  vesicles, during the synthesis of new cross-walls
  during cytokinesis are perpendicular to cell
  plate.
• Sporopollenin in charophycean zygote prevents
  dessication.
• Integral for success of terrestrial plants.

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3. Several terrestrial adaptations distinguish
land plants from charophycean algae

• Several characteristics separate the four land
  plant groups from their closest algal relatives,
  including
• apical meristems
• multicellular embryos dependent on the parent
  plant
• alternation of generations
• sporangia that produce walled spores
• gametangia that produce gametes

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• The elongation and branching of the shoots and
  roots maximize their exposure to environmental
  resources.
• This growth is sustained by apical meristems,
  localized regions of cell division at the tips of
  shoots and roots.
• Cells produced by meristems differentiate into
  various tissues, including surface epidermis
  and internal tissues.

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• Multicellular plant embryos develop from zygotes
  that are retained within tissues of the female
  parent.
• This distinction is the basis for a term for all
  land plants, embryophytes.

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• All land plants show alternation of generations
  in which two multicellular body forms alternate.
• One of the multicellular bodies is called the
  gametophyte with haploid cells.
• Gametophytes produce gametes, egg and sperm.
• Fusion of egg andsperm duringfertilizationform
  a diploidzygote.

reproductive cell that can develop into a new
organism without fusing with another cell.
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• Plant spores are haploid reproductive cells that
  grow into a gametophyte by mitosis.
• Spores are covered by a polymer called
  sporopollenin, the most durable organic material
  known.
• This makes the walls of spores very tough and
  resistant to harshenvironments.

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• Multicellular organs, called sporangia, are found
  on the sporophyte and produce these spores.
• Within a sporangia, diploid spore mother cells
  undergo meiosis and generate haploid spores.
• The outer tissues of the sporangium protect the
  developing spores until they are ready to be
  released into the air.

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• The gametophytes of bryophytes, pteridophytes,
  and gymnosperms produce their gametes within
  multicellular organs, called gametangia.
• A female gametangium, called an archegonium,
  produces a single egg cell in a vase-shaped
  organ.
• The egg is retained within the base.

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• Male gametangia, called antheridia, produce many
  sperm cells that are released to the environment.
• The sperm cells of bryophytes, pteridiophytes,
  and some gymnosperms have flagella and swim to
  eggs.
• A sperm fuses with an egg within an archegonium
  and the zygote then begins development into an
  embryo.

Fig. 29.9b
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1. The three phyla of bryophytes are mosses,
liverworts, and hornworts

• Bryophytes are represented by three phyla
• phylum Hepatophyta - liverworts
• phylum Anthocerophyta - hornworts
• phylum Bryophyta - mosses
• Note, the name Bryophyta refers only to one
  phylum, but the informal term bryophyte refers
  to all nonvascular plants.

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2. Phylum Bryophyta (Mosses)

• Peat bogs used as energy resource, antiseptics,
  commercial cropland (cranberry/blueberry)
• Gametophyte generation dominant.
• Most lack conductive tissues small, rely on
  diffusion.
• Leaf-like tissues lack cuticle, easy water
  absorption. (few exceptions)
• Bryophyte spores germinate in favorable habitats
  and grow into gametophytes by mitosis.
• The gametophyte is a mass of green, branched,
  one-cell-thick filaments, called a protonema.
• Rhizoids are used for anchorage.
• Rhizoids are not composed of tissues.
• They lack specialized conducting cells.

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Life Cycle of Typical Bryophyte
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Hornwort
Liverwort
Male Gametophyte
Female Gametophyte
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Traecheophytes Vascular Plants

• Modern vascular plants have food transport
  tissues (phloem) and water conducting tissues
  (xylem) with lignified cells.
• Have true roots, stems, and leaves.
• Sporophyte generation is dominant and is
  independent of the parent gametophyte.
• The gametophytes are tiny plants that grow on or
  just below the soil surface.
• This reduction in the size of the gametophytes is
  even more extreme in seed plants.
• The first vascular plants, pteridophytes, were
  seedless.

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• A heterosporous sporophyte produces two kinds of
  spores.
• Megaspores develop into females gametophytes with
  archegonia. Produce eggs.
• Microspores develop into male gametophytes with
  antheridia. Produce sperm.
• A homosporous sporophyte produces one kind of
  spore that develops into a gametophyte with both
  antheridia and archegonia on the same structure.

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Seedless Vascular Plants

• The seedless vascular plants, the pteridophytes
  consists of two modern phyla
• division Lycophyta - lycophytes
• division Pterophyta - ferns, whisk ferns, and
  horsetails
• These phyla probably evolved from different
  ancestors among the early vascular plants.

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Division Lycophyta

• Club Mosses. Formed forests during Carboniferous
  period.
• low-growing understory plants and epiphytes.
  Most common in wet tropics.
• Leaves each have a single unbranched vein
  therefore called a microphyll. (Leaves with
  branched veins are called megaphylls.)
• Special leaves called sporophylls produce a
  sporangium on top, near the point where they
  attach to the stem.
• Most species are homosporous, produces a single
  type of spore.
• This spore develops into a bisexual gametophyte
  with both archegonia (female sex organs) and
  antheridia (male sex organs).

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Division Sphenophyta

• One extant genus, Equisetum. Known as horsetail,
  foxtail, or scouring rush.
• Stores silica in cell wall.
• form underground stems known as rhizomes
• At the tips of reproductive branches are the
  "cones," or strobili
• Homosporous

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Strobilus, spore producing structure
Stem, Internode
Leaves
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Lycophyta. The Psilophytes
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Division Pterophyta

• Most dominant seedless, vascular plant.
• large megaphyllous leaves (fronds) with an
  extensively branched vascular system. Often
  divided into leaflets or pinnae.
• produce clusters of sporangia, called sori, on
  the back of green leaves (sporophylls)
• Homosporous.

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sporangia
indusium
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Life Cycle of a Typical Fern
sperm produced in an antheridium must travel
through a film of water in order to reach the egg
of an archegonium to form zygote.