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Chapter 29

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Chapter 29

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  1. Chapter 29 Plant Diversity IHow Plants Colonized Land

  2. Plants are classified in 4 main divisions (aka phyla) according to whether or not they contain vascular tissue and whether or not they produce seeds, flowers, & fruits

  3. Concept 29.1: Land plants evolved from green algae Unicellular green algae are primitive ancestors of land plants • presence of chlorophyll a & b & energy storage via starch supports lineage Multicellular Green algae called charophytes are closest relatives • Nuclear & chloroplast gene comparisons support lineage from ancestor common with charophytes • Outer layer of a durable polymer allows charophyte zygotes to germinate out of water

  4. Derived Traits of Plants absent in the charophyceans, present in plants: • Apical meristems • Alternation of generations lifecycle • Walled spores produced in multicellular sporangia • Multicellular gametangia • Multicellular dependent embryos

  5. Apical Meristems --buds at end of shoots & roots from which primary (length) growth occurs LE 29-5a Apical Meristem of shoot Developing leaves Apical meristem Shoot Root 100 µm 100 µm

  6. Alternation of Generations Lifecycle of all plants • 1n multicellular gametophytes produce gametes by mitosis. • Gamete fertilization produces 2n sporophytes. • Meiosis of 2n sporophyte cells produces 1n spores that • develop by mitosis into gametophytes gametophyte Gametes Spores Mitosis MEIOSIS FERTILIZATION Zygote Diploid multicellular organism (sporophyte) Mitosis

  7. LE 29-5c Walled Spores Produced in Sporangia Multicellular Gametangia Multicellular, Dependent Embryos Byrophyte walled (enclosed) sporangia, multicellular gametangia, & multicelluar embryos that develop within the female gametophyte, the archegonium. Archegonium with egg Longitudinal section of Sphagnum sporangium (LM) Female gametophyte Spores Embryo Maternal tissue Sporangium 10 µm 2 µm Sporophyte Antheridium with sperm Male gametophyte Gametophyte Archegonia and antheridia of Marchantia (a liverwort) Sporophyte and sporangium of Sphagnum (a moss)

  8. Other derived traits such as a cuticle, true leaves & vascular tissues evolved in many plant species • A cuticle is a waxy coating on leaves that helps prevent drying (desiccation) • Leaves are plant organs adapted for photosynthesis • Vascular tissue transports water (xylem) or dissolved organic molecules—food (phloem)—within the plant

  9. LE 29-7 Land plants Vascular plants Bryophytes Seedless vascular plants Seed plants Gymno- sperms Angio- sperms Hornworts Mosses Liverworts Lycophytes Pterophytes Charophyceans Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Origin & Diversification of Plants: Seed plants are better adapted, in general, to reproduce and develop in terrestrial niches.

  10. Bryophytes: Nonvascular seedless plantshabitat: moist areas, tolerant to cold (dominant plants in the tundra biome) Only bryophytes are nonvascular plants; they are adapted for diffusion of materials between their cells & moist habitats. Only bryophytes have a dominant (bigger, form for most of its lifecycle) haploid gametophyte generation; gametophytes are low to the ground (like carpets), have a thin thallus (body). The antheridia of the gametophyte produces flagellated swimming sperm; moist habitats are essential for reproduction. The archaegonia contain eggs (ova) that are fertilized inside the multicellular archaegonia, and the 2n embryo develops inside it. It’s smaller 2n sporophyte generation grows out of the gametophyte’s archegonium & persists a short time before bursting to release haploid meiotic sporesnew gametophytes

  11. LE 29-8 Raindrop Key Male gametophyte Haploid (n) Diploid (2n) Sperm “Bud” Spores develop into threadlike protonemata. A sperm swims through a film of moisture to an archegonium and fertilizes the egg. • Bryophyte Life Cycle Antheridia The haploid protonemata produce “buds” that grow into gametophytes. Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Protonemata “Bud” Egg Gametophore Spores Female gametophyte Archegonia Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores. Rhizoid Peristome The sporophyte grows a long stalk, or seta, that emerges from the archegonium. FERTILIZATION Sporangium (within archegonium) MEIOSIS Seta Calyptra Zygote Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium The diploid zygote develops into a sporophyte embryo within the archegonium. Young sporophyte Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. Female gametophytes Capsule with peristome (SEM)

  12. LE 29-9d Polytrichum commune, hairy cap moss Moss gametophyte & sporophyte Sporophyte Gametophyte

  13. Plants are classified in 4 main divisions (aka phyla) according to whether or not they contain vascular tissue and whether or not they produce seeds, flowers, & fruits

  14. Life Cycles with Dominant 2n Sporophytes and vascular tissues, but without seeds. Ferns (pterophytes), whiskferns, club mosses, & horsetails are seedless, vascular plants. In contrast with bryophytes, sporophytes of these & all other vascular plants are the dominant generation. Having a diploid form most of its lifecycle is an adaptation protecting land plants from UV light. Having vascular tissues allows efficient liquid transport through thicker bodies & out of soil via roots. Vascular tissues of plants are analogous to circulatory systems in animals.

  15. LE 29-12 Key Haploid (n) Diploid (2n) Fern lifecycle: Tiny, free living 1n gametophytes out of whose archaegonia larger sporophytes develop then produce sori releasing 1n meiotic spores for new gametophytes. Antheridium Spore Young gametophyte MEIOSIS Sporangium Sperm Archegonium Egg New sporophyte Mature sporophyte Sporangium Zygote FERTILIZATION Sorus Fiddlehead Gametophyte

  16. Transport in Xylem and Phloem • Vascular plants have two types of vascular tissue: xylem and phloem • Xylem conducts most of the water and minerals and in ferns includes dead cells called tracheids; this is why vascular plants are called tracheophytes. • Phloem consists of living cells and distributes sugars, amino acids, and other organic products • Roots are plant organs that anchor plants & absorb minerals from soil; they contain vascular tissue.

  17. Most plants are heterosporous, w/ meiotic 1n spores developing to a male or female, but some are homosporous, giving rise to both sperm & eggs.

  18. Classification of Seedless Vascular Plants • There are two phyla of seedless vascular plants: • Lycophyta includes club mosses, spike mosses, and quillworts • Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

  19. LE 29-14f Athyrium filix-femina, lady fern

  20. Seedless vascular plants like tree ferns & giant club mosses dominated carboniferous forests & formed much of today’s coal.

  21. Adaptations for terrestrial life seen in allplants are • chlorophylls a and b. • cell walls of cellulose and lignin. • Zygotes developing within archaegonia • vascular tissue and stomata. • alternation of generations.

  22. 2. A botanist discovers a new species of plant in a tropical rain forest. After observing its anatomy and life cycle, the following characteristics are noted: flagellated sperm, xylem with tracheids, separate gametophyte and sporophyte phases, and no seeds. This plant is probably most closely related to * • mosses. • Chara. • ferns. • liverworts. • flowering plants.