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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 29 Plant Diversity I: How Plants Colonized Land
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 29-1 KNOW THIS * *
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: The Greening of Earth roughly 290,000 living species of plants Plants supply oxygen and are the ultimate source of most food eaten by land animals Green algae called charophytes are the closest relatives of land plants
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Morphological and Molecular Evidence Many characteristics of land plants also appear in a variety of algal clades, mainly algae However, land plants share four key traits only with charophytes: Concept 29.1: green algae Land plants – Rose-shaped complexes for cellulose synthesis – Peroxisome enzymes – Structure of flagellated sperm – Formation of a phragmoplast
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Comparisons of both nuclear and chloroplast genes seem to indicate that land plants share a common ancestor with modern charophytes Figure 29.3 Examples of charophytes, the closest algal relatives of land plants
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adaptations Enabling the Move to Land Good: unfiltered sun, more CO 2, nutrient-rich soil, few herbivores or pathogens Bad: a scarcity of water and lack of structural support In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants Systematists are currently debating the boundaries of the plant kingdom Some biologists think the plant kingdom should be expanded to include some or all green algae Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae (sigh!) More whining over irrelevant stuff
Fig ANCESTRAL ALGA Red algae Chlorophytes Charophytes Embryophytes Viridiplantae Streptophyta Plantae
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Derived Traits of Plants Four key traits appear in nearly all land plants but are absent in the charophytes: 1.Alternation of generations 2.Walled spores produced in sporangia 3.Multicellular gametangia 4.Apical meristems - tips of shoots/roots with cells that are totipotent This stuff is explained in the next few slides
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings cuticle – waxy covering to reduce water loss Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients Plants still do this: “mycorrhizae” Fungus gets sugars from plant. Plant gets water and soil minerals from fungus. Absorbs more water/nutrients this way than it could normally Additional traits in many plants Now, onto the four derived traits
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations 1. Alternation of Generations
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Alternation of Generations Two multicellular stages gametophyte is haploid and produces haploid gametes by mitosis Sporophyte is diploid, makes haploid spores by meiosis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Huh? Plants with a placenta? many land plants are embryophytes diploid embryo stays in tissue of the female gametophyte embryophytes - embryo depends on the parent Nutrients transferred from parent to embryo in placental transfer cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 2. Walled Spores Produced in Sporangia Sporophyte (2n) makes spores (n) in organs called sporangia sporocytes cells (2n) meiosis spores (n) Spore walls contain sporopollenin, which makes them resistant to harsh environments 2n n via meiosis? Plants can occasionally do normal things
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3. Multicellular GametangiaWhat!?!?!? Gametes made in organs called gametangia ♀ gametangia = archegonia makes eggs Site of fertilization Gametophytes (n) make gametes (n) via mitosis ♂ gametangia = antheridia make & release sperm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 4. Apical Meristems – stem cells at tips Plants sustain continual growth in their apical meristems – apex (tip/outer edge) Cells of apical meristems differentiate into various tissues Root tips Stem tip
Derived Traits of Plants Four key traits appear in nearly all land plants but are absent in the charophytes: 1.Alternation of generations 2.Walled spores produced in sporangia 3.Multicellular gametangia 4.Apical Meristems review
Fig. 29-UN4 Gametophyte Mitosis Spore Gamete Mitosis n n n n 2n MEIOSISFERTILIZATION Zygote Sporophyte Haploid Diploid Alternation of generations Apical meristems Multicellular gametangia Walled spores in sporangia Archegonium with egg Antheridium with sperm Sporangium Spores Apical meristem of shoot Developing leaves
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Origin and Diversification of Plants Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized spores and tissues have been extracted from 475-million-year-old rocks
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ways to group or classify plants - vessels Most land plants have vascular tissue mosses and liverworts Nonvascular plants are bryophytes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9b Plagiochila deltoidea, a “leafy” liverwort
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9c An Anthoceros hornwort species Sporophyte Gametophyte
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Seedless vascular plants are actually paraphyletic, but are divided into – Lycophytes (club mosses and their relatives) – Pterophytes (ferns and their relatives) Seedless vascular plants: two types
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Seed plants form a clade and can be divided into further clades: seed = embryo, nutrients & a protective coat – Gymnosperms, the “naked seed” plants, including the conifers – Angiosperms, the flowering plants
Table 29-1
Fig Origin of land plants (about 475 mya) Origin of vascular plants (about 420 mya) Origin of extant seed plants (about 305 mya) ANCES- TRAL GREEN ALGA Liverworts Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Pterophytes (ferns, horsetails, whisk ferns) Gymnosperms Angiosperms Seed plants Seedless vascular plants Nonvascular plants (bryophytes) Land plants Vascular plants Millions of years ago (mya)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta Mosses are most closely related to vascular plants
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Gametophytes In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes In other plants this is usually the opposite!!! Sporophytes usually only present part of the time
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gametophyte: composed of a protonema and gamete-producing gametophore Rhizoids anchor gametophytes to substrate Small because no vascular tissues Mature gametophytes sperm in antheridia and egg in archegonium Sperm swim through a film of water to reach and fertilize the egg spore gametophyte
Fig. 29-9a Thallus Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) Sporophyte Foot Seta Capsule (sporangium) 500 µm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Sporophytes Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome Hornwort and moss sporophytes have stomata for gas exchange
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9d Gametophyte Seta Capsule Sporophyte (a sturdy plant that takes months to grow) Polytrichum commune, hairy-cap moss
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Ecological and Economic Importance of Mosses Mosses are capable of inhabiting diverse and sometimes extreme environments, but are especially common in moist forests and wetlands Some mosses might help retain nitrogen in the soil
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum is an important global reservoir of organic carbon
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall Bryophytes and bryophyte-like plants are though to be the main vegetation for first 100 million years of plants Vascular plants began to diversify during the Devonian and Carboniferous periods
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall Vascular tissue = taller plants Seedless = swimming sperm Need moist environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Traits of Vascular Plants Living vascular plants are characterized by: Life cycles with dominant sporophytes Vascular tissues called xylem and phloem Well-developed roots and leaves
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Cycles with Dominant Sporophytes In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern The gametophytes are tiny plants that grow on or below the soil surface Animation: Fern Life Cycle Animation: Fern Life Cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Two types of vessels: Xylem and Phloem Xylem conducts most of the water and minerals and includes dead cells called tracheids Phloem consists of living cells and distributes sugars, amino acids, and other organic products
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transport in Xylem and Phloem Water-conducting cells are strengthened by lignin and provide structural support Increased height was an evolutionary advantage
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Roots Roots are organs that anchor vascular plants They enable vascular plants to absorb water and nutrients from the soil Roots may have evolved from subterranean stems
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Leaves Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Leaves are categorized by two types: – Microphylls, leaves with a single vein – Megaphylls, leaves with a highly branched vascular system microphylls may have evolved first as outgrowths of stems
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Leaves are categorized by two types: – Microphylls, leaves with a single vein – Megaphylls, leaves with a highly branched vascular system microphylls may have evolved first as outgrowths of stems
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sporophylls and Spore Variations Sporophylls are modified leaves with sporangia Sori are clusters of sporangia on the undersides of sporophylls
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sporophylls and Spore Variations Strobili are cone-like structures formed from groups of sporophylls
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Most seedless vascular plants are homosporous Spore develops into a bisexual gametophyte Homosporous = has one type of spore
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings megaspores ♀ gametophytes, microspores ♂ gametophytes All seed plants and some seedless vascular plants are heterosporous Heterosporous = has two types of spore
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Two Phyla of Seedless Vascular Plants 1. Phylum Lycophyta includes club mosses, spike mosses, and quillworts
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Two Phyla of Seedless Vascular Plants 2. Phylum Pterophyta includes ferns, horsetails, and whisk ferns and their relatives
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts Giant lycophytes thrived for millions of years in moist swamps Surviving species are small herbaceous plants Club mosses/spike mosses = vascular = not true mosses
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives Ferns: most diverse of seedless vascular Horsetails were diverse during the Carboniferous period, but are now restricted to the genus Equisetum Whisk ferns resemble ancestral vascular plants but are closely related to modern ferns
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ancient Lycophyte forests Devonian and Carboniferous forests of horsetails and ferns These Carboniferous forests = our coal
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1.Describe four shared characteristics and four distinct characteristics between charophytes and land plants 2.Distinguish between the phylum Bryophyta and bryophytes 3.Diagram and label the life cycle of a bryophyte 4.Explain why most bryophytes grow close to the ground and are restricted to periodically moist environments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5.Describe three traits that characterize modern vascular plants and explain how these traits have contributed to success on land 6.Explain how vascular plants differ from bryophytes 7.Distinguish between the following pairs of terms: microphyll and megaphyll; homosporous and heterosporous 8.Diagram and label the life cycle of a seedless vascular plant
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