ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty-Three Outline INTRODUCTION Plants Are Dominant Photosynthetic Organisms on Land Basic Characteristics of Plant Kingdom Multicellular eukaryotes Possess cellulose-rich cell walls, store starch Have chloroplasts containing chlorophylls a and b, carotenoids THE EVOLUTIONARY ORIGINS OF PLANTS Plants Derived From Multicellular Green Algae Biochemical and morphological similarities Only organisms that form cell plate during mitosis Plants Divided into Twelve Phyla fig 33.1 Terms phylum and division are interchangeable, the former is preferred Old term "bryophyte" now constitute now three separate phyla Lack or have poorly developed vascular strands Include mosses, liverworts and hornworts Vascular plants are subdivided into nine phyla Have food and water conducting strands Include ferns, conifers, and flowering plants Share a semiterrestrial green algal ancestor 430 million years old THE GREEN INVASION OF THE LAND Plants Occur Almost Exclusively on Land Characteristic shared with arthropods and fungi Most likely that they all evolved on land Plant cell walls provide protection from desiccation Relatively impermeable outer cuticle formed from waxy cutin Stoma allow passage of gases for photosynthesis fig 33.2 Stoma also allow passage of water vapor Evolution of Vascular Systems Systems capable of efficient conduction of liquids fig 33.3 Helped achieve ecological dominance on land Specialized strands of elongated cells Travel from roots through stems to leaves Conduct water and minerals from roots, carbohydrates from leaves Early vascular plants had well-developed conducting systems fig 33.4 Adaptation to Terrestrial Habitats Enhanced by mycorrhizal fungi Features of plants themselves Specialization of parts above and below the ground: shoots, roots Expansion of photosynthetic areas: leaves Specializations in reproductive features THE PLANT LIFE CYCLE Alternation of Generations Alternation of diploid sporophyte with haploid gametophyte fig 33.5 Generalized life cycle In sporophyte, meiosis in spore mother cells produces haploid spores Spores divide by mitosis to produce multicellular diploid gametophyte Gametophyte produces haploid gametes Gametes fuse forming diploid zygote Zygote mitotically divides to form sporophyte Specialization in the Plant Life Cycle Liverwort, moss and fern gametophytes are small and free living Moss and liverwort gametophyte dominates, sporophyte reduced Vascular plant Are primarily sporophytic, gametophytes are reduced Gametophytes dependent on, enclosed within sporophyte MOSSES, LIVERWORTS AND HORNWORTS Traditionally Grouped Together as Bryophytes fig 33.6 Gametophytes nutritionally independent of sporophyte Sporophyte attached to gametophyte, partially nutritionally dependent on it Not derived from common ancestor separate from ancestor of vascular plants Ecology Common in tropical and temperate moist habitats Most abundant plants in Arctic and Antarctic, rare in deserts Require free water for sexual reproduction growth and development Mosses are sensitive to pollutants Primary Characteristics Small gametophyte is green, manufactures own food fig 33.1a;8 Gametophyte larger and more conspicuous than sporophyte Sporophyte may be completely enclosed in gametophytic tissue Sporophyte smaller than and derives food from gametophyte Presence of vascular tissue Liverworts and hornworts lack conducting tissue Mosses possess conducting tissue Carry water in sporophyte stems and sometimes gametophyte Possess tissues that resemble tissues that carry food in vascular plants Mosses may share common ancestor with vascular plants, not liver/hornworts May or may not have distinct leaves and stems Mosses have leaves and stems Liverworts and hornworts are strap shaped No anatomical differentiation between above- and below-ground parts Possess colorless, non-absorptive, anchoring rhizoids FEATURES OF VASCULAR PLANTS Fossil Vascular Plants Rhyniophyta: simple branching axis with sporangia at tips fig 33.4 Evolution of first leaves and more complex sporangia Vascular Versus Non-Vascular Plants Large, dominant, nutritionally independent sporophytes fig 33.3 Specialized leaves, stems, roots, cuticles and stomata fig 33.2 Evolution of seeds Growth in Vascular Plants Early plants exhibited primary growth Cell division at tips of plant body increases length Presence of well-marked vascular cylinders No specialization into stems, leaves and roots Development of secondary growth Cell division occurs in regions around periphery Conducting tissues multiplied into cylindrical zone Enables increase in diameter of plant, allows for tree-like height Evolved independently in different groups Conducting Systems of the Vascular Plants Sieve elements Soft-walled phloem cells Carry carbohydrates away from area where manufactured Tracheary elements Hard-walled xylem cells Transport water and minerals up from roots May be associated together in vascular strands Seeds Embryo protected within coat of sporophyte tissue Characterized by gymnosperms and angiosperms First appeared 360 million years ago Both kinds of gametophytes reduced Anatomical characteristics fig 33.7 Young sporophyte, the embryo, arrested in an embryonic state Surrounded by tough, drought-resistant, protective seed coat Also contains products of mature megagametophyte Adaptive importance Aids in dispersal Protects embryonic plant from drying out Protects embryo`s food store from predators or parasites Food storage analogous to yolk of egg SEEDLESS VASCULAR PLANTS History Earliest vascular plants lacked seeds Four living and three extinct phyla lack seeds Pterophyta: The Ferns Most abundant group Include small, reduced aquatic ferns fig 26.6b Include tree ferns of great size fig 33.8 Temperate plants are herbaceous with rhizomes, fronds and roots Nearly all are homosporous with dominant sporophyte Sporophyte large and conspicuous More complex than gametophyte Nutritionally independent of gametophyte Comparison to moss Fern sporophyte more developed, independent and dominant Fern more complex with vascular tissue, roots, stems and leaves Other Phyla of Seedless Plants Includes Psilophyta (whisk ferns), Lycophyta (club mosses), Sphenophyta (horsetails) Share many common features Form archegonia and antheridia Produce free-swimming sperm that require water for fertilization Comparable features of seed plants Have nonflagellated sperm None form archegonia, few form antheridia SEED PLANTS Evolution and Ecology Derived from single, common ancestor Five phyla Include angiosperms, flowering plants In only angiosperms are ovules completely enclosed by sporophyte tissue at pollination Other four phyla collectively termed gymnosperms Reproduction Male and female gametophytes develop within sporophyte Gametophyte completely dependent on sporophyte Immature male gametophytes called pollen grains Carried to female during pollination Germinates forming pollen tube with sperm cells No free water required for fertilization Advancement of seed Protects embryo Enhances dispersal Precludes need for water Gymnosperms Ovules are not completely enclosed by sporophyte tissue at pollination Include conifers, cycads, ginkgoes and gnetophytes fig 33.9 Name means "naked seed" Characteristics of diverse groups Motile sperm in cycads and ginkgo Some have archegonia, others don`t Conifers are most familiar group fig 33.9a Include pine, spruce, fir, hemlock and cypress Most have needle-like leaves Generally grow in moderately dry areas Cycads have short stems and palm-like leaves fig 33.9b Ginkgo has fan shaped leaves fig 33.9c Gnetophytes differ greatly from one another fig 33.9d The Pine Life Cycle fig 33.10 Life cycles of conifers similar Cycle usually complete in one growing season (pine takes two) Angiosperms Ovules enclosed by sporophytic tissue at pollination Structures called carpels fig 33.11 Pollination indirect Pollen grain reaches specialized portion called stigma Pollen tubes grow through style to ovary Ovary contains ovules, each contains an egg Pollination in gymnosperms is direct Ovules exposed to air (not enclosed) Pollen reaches ovule directly Carpel grows into characteristic fruit, encloses seeds Not directly evolved from living phyla of gymnosperms Angiosperm flower composed of four whorls fig 33.12 Innermost whorl collectively called gynoecium Carpels fold around ovules Stigma separated from body of carpel by style Pollen tube grows through stigma and style Reaches lower portion called ovary Separate or fused carpels called pistils Next whorl below is androecium Individuals called stamens Composed of filament plus anther fig 33.11 Anther contains four microsporangia or pollen sacs Microspore mother cells produce microspores Microspores develop into pollen grains Pollen shed at either two- or three-celled stage Mature microgametophytes have three cells Two are sperm cells Third is tube cell that grows into pollen tube Two outermost whorls called perianth Corolla, below stamens, is composed of petals Outermost calyx is composed of sepals Pollen carried by numerous animals Enhanced by various reward systems like nectar from nectaries Evolution of floral characteristics associated with pollination Some plants self-pollinate, exhibit inbreeding Four cells initially produced via meiosis Three disintegrate, on survives Meiosis occurs within nucellus which is enfolded by integuments Ovule = integuments + nucellus fig 33.11 Angiosperms exhibit unique process of double fertilization First sperm fuses with egg and forms zygote Second sperm fuses with polar nuclei Forms triploid primary endosperm nucleus Gives rise to nutritive endosperm fig 33.13 Developing embryos derive nutrition from endosperm Example: bean and pea Endosperm transfers to embryo when seed is mature Seedling leaves are swollen and fleshy, contain food reserves Example: corn Seed contains abundant endosperm Embryo draws on endosperm as it germinates Summary of angiosperm life cycle fig 33.14 A Very Successful Group Exhibit alternation of generations Appearance of seed parallels reduction of gametophyte