Plants: Topic 12 PDF

Plants BIOL 108 Andrea Botero Plant cell Cell wall composed of cellulose Large central vacuole Chloroplasts Plants Eukaryotes Almost all are photoautotrophs ALL multicellular Sessile (can’t move around) Plants: Life cycle Alternation of generations: Two multicellular stages...

Plants BIOL 108 Andrea Botero Plant cell Cell wall composed of cellulose Large central vacuole Chloroplasts Plants Eukaryotes Almost all are photoautotrophs ALL multicellular Sessile (can’t move around) Plants: Life cycle Alternation of generations: Two multicellular stages 1. Haploid: Sporophyte (Phyte=plant→ “Spore producing plant”) Produces spores by mitosis 2. Diploid: Gametophyte (“Gamete producing plant)” Produces gametes by meiosis Gamete: reproductive cell  Plants: Life cycle 1. Sporophyte (2n) produces spores (n) 2. Spore germinates and divide by mitosis 3. Produces multicellular gametophyte (n) 4. Gametophyte produces gametangia that contains eggs and sperm 5. Gametes fuse and produce sporophyte  Plants’ evolution 1. Photosynthesis → atmosphere from reducing to oxidizing 2. Cyanobacteria first to adapt to intertidal zones and spread into shallow coastal streams followed by fungi and green algae 3. Adaptative changes in plants appeared 4. New features → dramatic radiation (rapid evolution and divergence) Plants’ evolution: Biochemical and structural adaptations 1. Early plants (Poikilohydric)→ little control over internal water content and do not restrict water loss Water content fluctuates with moisture levels in environment Drought tolerant 2. Plants evolved to regulate water content and restrict water loss Thicker, more extensive cuticles and stomata (pores in cuticle that regulate water loss) Water transport tissue that provide support for upright growth Plants’ evolution: Association with fungi Bacteria, protists and fungi colonized before 80% plants symbiotic association with mycorrhizae Plant provides C Fungus increases nutrients supply Essential association for plant evolution and success because first plants lacked roots and soil of early earth was nutrient poor Plants’ evolution: Lignified water conducting cells Initially plants short → helped with moisture retention but ineffective at capturing light Plants require strengthening tissue to grow upright and internal water circulation (diffusion ineffective over long distances) Solved with lignin synthesis Deposits in cell walls of xylem Provide support Xylem vascular tissue accompanied by phloem, conduct water and nutrients Present in vascular plants Non-vascular plants have different tissues to move water and nutrients, homologous but not vascular tissue Plants’ evolution: Apical meristems Regions of constantly dividing cells near the tips of shoots and roots that produce all tissues of the plant body. Foundation for a vascular plant’s extensively branching stem and root systems Plants’ evolution: Shoot systems Sturdy stems→ basis for aerial shoot system Root system→ anchoring, water and nutrient absorption Underground, cylindrical, absorptive structures with large surface area Shoot system → Stems and leaves that arise from apical meristem, absorb light and CO2 Lignin was crucial Increased light interception More efficient reproduction Plants’ evolution: Shoot systems Leaves: Modifications of stems Arouse several times during evolution Can be divides into: Microphylls→ narrow with only one vein Megaphylls→ broader with multiple veins Plants’ evolution: Life cycle Early land plants evolved multicellular diploid sporophyte stage In mosses and other non-vascular plants sporophyte is dependent on haploid gametophyte stage As plants evolved gametophyte (n) became smaller and less complex with shorter life span and sporophyte (2n) became the dominant stage of life Trend towards diploid dominance reflects advantage of being diploid in land environments Plants’ evolution: Separate female and male gametophyte Plants can be : Homosporous: produce one type of spore which develops into a gametophyte (n) with both male and female organs. Heterosporous: Two types of spores in two different sporangia Microspores → develop into male gametophyte Megaspores→ develop into female gametophyte Bryophytes: Nonvascular plants Colonize bare land Trap particles of organic and inorganic matter→ build soil Bridge aquatic and land environments Bryophytes: Nonvascular plants Poikilohydric → small and commonly grow on wet sites, some in dry environments Produce flagellated sperm that swims to reach egg Lack xylem and phloem Parts: Rhizoids→ Only provide anchorage Steamlike structures Leaflike structures Bryophytes: Nonvascular plants Life cycle Multicellular gametophyte and sporophyte phases, but the sporophyte is permanently associated with the gametophyte and lives shorter than gametophyte Bryophytes: Nonvascular plants Life cycle 1. Green leafy gametophyte develops diploid sporophytes 2. Egg fertilized by sperm and originates diploid embryo sporophyte that remains attached to gametophyte 3. Sporophyte produces spores that germinate and produce a new gametophyte Bryophytes: Nonvascular plants Life cycle Green leafy gametophyte develops diploid sporophytes Gameophytes produce gametes inside protected organ (gametangium) Gametangia in which eggs are produced are flask-shaped structures called archegonia Gametangia in which flagellated sperm is called antheridia Bryophytes: Nonvascular plants Life cycle Sporophyte Unlike vascular plants Gametophyte: Longer lived than the sporophyte Photosynthetic Sporophyte: Remains attached to the gametophyte Depends on the gametophyte for much of its nutrition. Gametophyte Bryophytes: Mosses Approximately 10,000 species Bryophytes: Liverworts 6,000 species Some are flat, branching, ribbonlike plate of tissue closely pressed against damp soil, Some are leafy and superficially resemble mosses, although the arrangement of leaves is different Bryophytes: Hornworts 100 species Sporophyte has a meristematic region at its base that produces new sporangium tissue and spores throughout the life of the sporophyte. Summary Seedless vascular plants Disperse by spores and have swimming sperm that require water to reach eggs Sporophyte (larger, longed-lived) independent of gametophyte (small) Well developed vascular system (Xylem and phloem) Seedless vascular plants: Lycophyta Club mosses, scale mosses and quillworts Most homosporous Seedless vascular plants: Pterophyta Ferns, whisk ferns, and horsetails. Ferns Plant body→ Sporophyte Produces aboveground cluster of leaves Seedless vascular plants: Pterophyta Ferns Sporangia produced on lower surface or margins of leaves (Sorus) Release spores Seedless vascular plants: Pterophyta Ferns Spores develop into gametophytes Small Heart shaped Anchored to soil by rhizoids Seedless vascular plants: Pterophyta Ferns Antheridia and archegonia develop on underside of gametophytes Sperm swims towards archegonium Fertilization Development of sporophyte Gymnosperms: First seed plants Conifers and their relatives gymnos :“naked,” Sperma:“seed.” Exposed seeds Sporophyte: Large trees or shrubs Reproductive adaptations: Pollen and pollination Ovule Seed Gymnosperms: Life cycle  Gymnosperms: First seed plants Reproductive adaptations: Ovules: Megaspores are not shed but retained in megasporangia on sporophyte Megaspores reduced to one per sporangium Megaspore gives rise to female gametophyte  Gymnosperms: First seed plants Reproductive adaptations: Pollen: Microspores are retained in microsporangia and enveloped in sporophyte tissue Each microspore produces male gametophyte → pollen grain Pollen grain transferred to female reproductive parts by air →pollination  Gymnosperms: First seed plants Reproductive adaptations: Seeds: Structure that forms when an ovule matures, after a pollen tube reaches it and a sperm fertilizes the egg. Parts: Embryo sporophyte Tissue surrounding embryo Seed coat Gymnosperms: Cycads and Ginkgoes Cycads Restricted to warm weather similar to small palms Ginkgoes Only living species Gingko biloba Fan shaped leavesUsed in tradicional Chinese medicine Gymnosperms vs Angiosperms Concept preview: Cotyledons Angiosperms: Flowering plants Most successful today 260,000 known species Most ecologically diverse plants on earth Angeion: “vessel” –Sperma: “Seed” Fruits that help protect and disperse seeds  Angiosperms: Flowering plants Classification based on morphology: Monocots: Embryos single cotyledon Eudicots: Embryos have two cotyledons  Angiosperms: Flowering plants Large, diploid sporophyte phase dominates life cycle Sporophyte retains nourishes smaller gametophyte Evolutionary advantages: More efficient xylem and phloem Double fertilization process in ovule that produces embryo and endosperm Ovule containing female gametophyte enclosed within ovary made of carpels After fertilization ovary develops fruit aid protection and dispersion Angiosperms: Flowering plants Angiosperms: Flowering plants Group Characteristics Common names Bryophytes Nonvascular plants Mosses, Liverworts and Hornworts Gametophyte dominant Free water required for fertilization Cuticle and stomata present in some Seedless vascular plants Sporophyte dominant Lycophyta: Club mosses, scale Free water required for fertilization mosses, quillworts Cuticle and stomata present Pterophyta: Ferns, whisk ferns, True roots horsetails Gymnosperms Vascular plants with naked seeds Cycadophyta: Cycads Sporophyte dominant Ginkgophyta: Ginkgo Fertilization by pollination Gnetophyta: Gnetophytes Cuticle and stomata present Coniferophyta: Conifers Megaphylls present Angiosperms Plants with flowers and seeds Monocots: Grasses, palm, lilies, protected inside fruits orchids, etc. Sporophyte dominant Eudicots: Most fruits, trees, roses, Fertilization by pollination beans, potato, etc Cuticle and stomata present Megaphylls present