PRESENT

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1 Chapter 29 Plants 29.1 Evolutionary History of Plants Domain Eukarya, kingdom Plantae Plants evolved from freshwater green algae 450 million years ago Both contain chlorophyll a and b and accessory pigments Both store excess carbohydrates as starch Both have cellulose in their cell walls Chara Land plants are most closely related to a group of freshwater green algae known as charophytes 1 Five major evolutionary events Each one an adaptation to a land existence 29.1 Evolutionary History of Plants common ancestor common green algal ancestor embryo protection vascular tissue flowers, double fertilization, endosperm, fruit megaphylls seeds Million Years Ago (MYA) Flowering plants Gymnosperms Ferns and allies Lycophytes Mosses Liverworts Charophytes PRESENT Bryophytes Seedless Seed Vascular Nonvascular Alternation of Generations Two multicellular individuals alternate, each producing the other Sporophyte (2n or diploid) Produces spores by meiosis Gametophyte (n or haploid) Produces gametes by mitosis Plants differ as to which generation is dominant (most conspicuous) Shift to sporophyte dominance - adapation to life on land

2 Alternation of Generations sporophyte (2n) Reproduction in the Size of the Gametophyte spores spores seed seed zygote (2n) (n) (n) gametes sporangium (2n) spore (n) G a m e t o p h y t e (n) rhizoids Moss roots roots roots rhizoids Fern Gymnosperm Angiosperm S p o r o p h y t e (2n) gametophyte (n) Gametophyte (n) Sporophyte (2n) 29.2 Nonvascular Plants Lack vascular tissue Lack true roots, stems, and leaves By definition, roots, stems, and leaves have vascular tissue Gametophyte generation is dominant Flagellated sperm swim to egg Three divisions Hornworts Liverworts Mosses 29.2 Nonvascular Plants Mosses (phylum Bryophyta) Found all over the world Mosses become dormant if the environment becomes dry Most mosses can reproduce asexually by fragmentation in addition to sexual reproduction Gametophyte is the dominant generation

3 Moss Life Cycle, Polytrichum sp. 4. The sporophyte: developing The mature sporophyte has a foot buried in female 3. The zygote: sporophyte gametophyte tissue, a stalk, and an upper capsule (the sporangium), where meiosis occurs and spores are produced. The zygote and developing sporophyte are retained within capsule the archegonium. Sporangium 5. The spore: When the calyptra and lid (operculum) of a capsule fall off, the spores are mature. One or two rings of teeth project inward stalk from the margin of Sporophyte teeth the capsule. The operculum teeth close the opening, except when zygote the weather is dry. 2. Fertilization: Flagellated sperm foot (n) sperm egg Spores produced in 6. Spore dispersal: antheridia swim in Spores are released external water to when they are most archegonia, each Archegonia likely to be dispersed bearing a single by air currents. egg. buds Antheridia Protonema 7. The immature gametophyte: 1. The mature A spore germinates gametophytes: into a male or female In mosses, the leafy protonema, the first gametophyte shoots stage of the male bear either antheridia and the female or archegonia, where gametophytes. gametes are produced by mitosis. Gametophytes 29.2 Nonvascular Plants Adaptations and Uses of Nonvascular Plants Can live on bare rock, fences, cracks of sidewalks Selective advantage to being small and simple Help convert rocks to soil Peat moss Used as fuel Holds water Used in gardens to improve soil rhizoids 29.3 Seedless Vascular Plants Vascular tissue Xylem conducts water and minerals Phloem transports organic nutrients Have true roots, stems, and leaves Sporophyte is the dominant generation Two groups: Lycophytes Ferns and their allies Seedless vascular plants produce windblown spores (not seeds) The Carboniferous Period Seedless vascular plants formed the great swamp forests of the Carboniferous period

4 29.3 Seedless Vascular Plants 29.3 Seedless Vascular Plants Lycophytes (phylum Lycophyta) Club mosses Rhizome sends up aerial stems Microphylls Sporangia on clubshaped strobili strobili leaves branches aerial stem rhizome root Steve Solum/Bruce Coleman, Inc. Ferns (phylum Polypodiophyta) Most abundant in warm, moist, tropical regions Leaves are called fronds and grow from rhizome Dominant sporophyte stage Produces wind-blown spores Spore germinates and forms small gametophyte Independent from the sporophyte Swimming sperm produced by antheridia Fern Diversity 7. The fronds: 1. The sporophyte: The sporophyte The sporophyte is develops a rootbearing rhizome dominant in ferns. from which the aerial fronds project. Sporophyte sori Polystichum 6. The zygote: The resulting leaflet sporophyte zygote begins its sporangium development inside an archegonium. As the distinctive first leaf appears above the prothallus, and as the roots develop below it, the sporophyte becomes visible. young sporophyte on gametophyte fiddlehead rhizome roots annulus Sorus 2. The sporangia: In this fern, the sporangia are located within sori (sing., sorus), on the underside of the leaflets. zygote Sporangium 5. Fertilization: Fertilization takes place when moisture is present, because the flagellated sperm must swim in a film of water from the antheridia to the egg within the archegonium. egg thallus (underside) sperm Archegonium Antheridium Gametophyte Steven P. Lynch 3. The spores: Within a Spores sporangium, meiosis occurs and spores are produced. When a sporangium opens, the spores are germinating released. spore 4. The gametophyte: A spore germinates into a prothallus (the gametophyte), which typically bears archegonia at rhizoids the notch and antheridia at the tip between the rhizoids.

5 Gymnosperms and Angiosperms Most plentiful plants in the biosphere today Seeds contain a sporophyte embryo and stored food within a protective coat Allows an embryo to survive during long periods of dormancy Gymnosperms Heterosporous Two types of spores Produce two types of gametophytes Male gametophyte produced by pollen grains» Pollination - deposition of pollen on a female gametophyte» Pollen tube - sperm pass through pollen tube to reach ovule Female gametophyte develops within ovule Pine Life Cycle 1. The pollen cones: The seed cones: Typically, the pollen The seed cones are larger cones are quite small than the pollen cones and 7. The sporophyte: and develop near the are located near the tips After fertilization, the tips of lower of higher branches. ovule matures and branches. becomes the seed 2. The pollen sacs composed of the (microsporangia): embryo, reserve A pollen cone has two food, and a seed pollen sacs that lie on coat. In the fall of the the underside of second season, the Sporophyte each scale. seed cone opens to release winged The ovules seeds. When (megasporangia): a seed germinates, seed wing seed cone The seed cone has two the sporophyte pollen cones ovules that lie on the embryo develops upper surface of each into a new pine tree. scale. An ovule contains a megasporangium. Pollen sac embryo seed coat seed cone scale pollen cone scale stored food seed (Female gametophyte) 3. Microspores: Within pollen sacs, each microsporocyte (microspore mother 6. The zygote: cell) undergoes Once a pollen grain zygote meiosis and produces microsporocyte reaches a seed cone, four microspores. megasporocyte it becomes a mature male gametophyte. A pollen tube digests Megaspore: its way slowly Within an ovule, a toward a female megasporocyte gametophyte and (megaspore mother discharges two cell) undergoes Microspores nonflagellated Mature female gametophyte meiosis, producing sperm. One of these four megaspores, of fertilizes an egg in archegonium which three an archegonium, and integument pollen grain egg Megaspore Pollination Mature male gametophyte 4. The pollen grain: pollen tube The pollen grain has two wings and is pollen grain sperm carried by the wind to the seed cone during pollination. 5. The female gametophyte: 200!m Only one of the megaspores undergoes mitosis and develops into a mature female gametophyte, having two to six archegonia. Each archegonium contains a single large egg lying near the ovule opening. Gymnosperms Most are cone-bearing On the surfaces of their cone scales are ovules Later become seeds s not completely enclosed by diploid Tissue - naked Conifers, cycads, ginkgoes, and gnetophytes (pollengrain): Phototake

6 Conifers Conifers Pine, spruce, fir, cedar, hemlock, redwood, and cypress Adapted to cold, dry weather Needlelike leaves conserve water with thick cuticle and recessed stomata Dominant sporophyte produces pollen cones and seed cones Other Gymnosperms Other Gymnosperms Cycads Resemble palms or ferns Plentiful in Mesozoic era at the time of dinosaurs Gingkoes Only one surviving species - Gingko biloba, the maidenhair tree Female trees produce fleshy seeds that give off a foul odor Gnetophytes Ephedra is only species in N. America

7 Angiosperms (phylum Magnoliophyta) More known species of angiosperms than all other types of plants combined Live in all types of habitats Seed develops from an ovule within an ovary Ovary becomes the fruit Produce covered seeds (not naked) Two classes Monocots - Monocotyledones Eudicots - Eudicotyledones Flower Parts Receptacle: tip of stalk that bears flowers Sepals (calyx): modified leaves that protect bud Petals (corolla): modified leaves, may be colorful Stamens: male reproductive structures Anther: pollen production Filament Carpel (pistil): female reproductive structures Stigma: for reception of pollen Style Ovary: ovule production anther filament stamens Generalized Flower receptacle stigma style ovary ovule carpel (pistil) pollen tube petals (corolla) sepals (calyx)

8 Flower Diversity Life cycle Sexual reproduction in flowering plants is dependent on the flower Produces both pollen and seeds Pollination can be by wind or pollinator Birds, bees, other insects and even bats Many flowers are adapted to attract quite specific pollinators Fruits Final product of a flower Aids in the dispersal of seeds Flowering Plant Life Cycle Fruits Stamen anther filament Carpel stigma style ovary ovule 2. The microsporangia: Pollen sacs of the anther are microsporangia, where each microsporocyte undergoes meiosis to produce four microspores. The megasporangium: First, an ovule within an ovary contains a megasporangium, where a megasporocyte undergoes meiosis to produce four megaspores. 7. The sporophyte: The embryo within a seed is the immature sporophyte. When a seed germinates, growth and differentiation produce the mature sporophyte of a flowering plant. fruit Sporophyte (mature ovary) seed (mature ovule) 1. The stamen: An anther at the top of a stamen has four pollen sacs. Pollen grains are produced in pollen sacs. Anther: : megasporangium stigma style 6. The seed: The ovule now develops into the seed, which contains an embryo and food enclosed by a protective seed coat. The wall of the ovary and sometimes adjacent parts develop into a fruit that seed coat embryo endosperm (3n) Seed The carpel: The ovary at the base of a carpel contains one or more ovules. The contents of an ovule change during the flowering plant life cycle. pollen sac (microsporangium) integument microsporocyte megasporocyte ovary pollen grain (mature male gametophyte) 5. Double fertilization: On reaching the ovule, the pollen tube discharges the integument pollen sperm. One of the two tube sperm migrates to and polar nuclei fertilizes the egg, forming sperm a zygote; the other unites sperm with the two polar nuclei, egg producing a 3n (triploid) endosperm nucleus. The pollen tube endosperm nucleus divides to form 4. The mature male gametophyte: A pollen grain that lands on the carpel of the same type of plant germinates and produces a pollen tube, which grows within the style until it reaches an ovule in the ovar y. Inside the pollen tube, the generative cell nucleus divides and produces two nonflagellated sperm. A fully germinated pollen grain is the mature tube cell nucleus Pollination generative cell antipodals polar nuclei egg synergids Embryo sac (mature female gametophyte) The mature female gametophyte: The ovule now contains the mature female gametophyte (embryo sac), which typically consists of eight haploid nuclei embedded in a mass of cytoplasm. The cytoplasm differentiates into cells, one of which is an egg and another of which contains two polar nuclei. Microspores Megaspores degenerating megaspores 3. Microspores: Each microspore in a pollen sac undergoes mitosis to become an immature pollen grain with two cells: the tube cell and the generative cell. The pollen sacs open, and the pollen grains are windblown or carried by an animal carrie r, usually to other flowers. This is pollination. Megaspores: Inside the ovule of an ovar y, three megaspores disintegrate, and only the remaining one undergoes mitosis to become a female gametophyte.