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Plants, Fun Gi,And the Colonization of Land

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Plants, Fun Gi,And the Colonization of Land Plants,Fun gi,and the Colonizationof Land Objectives Introduction Explain the significanceof mycorrhizae to plant health. l7.l Compare the structure of multicellular algae and plants. Explain how plants are adapted to life on land. Plant Evolutionand Diversity 17.2 Explain how the first terrestrialplants evolved. Describe the structureof charophyceans and the plantscalled Coolcsonia. 17.3 Distinguishbetween bryophytes, seedless vascular plants, gymnospenns, and angiosperms. 17.3 Describethe four key adaptationsfor life on land that evolvedin plants. Alternation of Generations and Plant Life Cycles 17.4 Describe the alternation of generationslife cycle. Explain why this cycle appearsto have evolved independentlyin different $oups of plants. 17.5,17.6 Describe the key eventsof the moss and fern life cycles. 17.7 Explain how coal formed. 17.7 Describe the conditions in which the gymnospermsbecame dominant. 17.8 Describe the stagesof the pine tree life cycle. 17.9 Describe the parts of a flower and list their functions. t7.t0 Describe the stagesof the angiospermtree life cycle. t7.tl Describe examplesof adaptationsthat promote seed dispersal. 17.12 Describe the significanceof angiospermsto humans. 17.t3 Explain how flowers are adapted to attract pollinators. L7.14 Describe the human impact on plant diversity. Explain the significance of this loss for humanity. Fungi 17.15 Describethe importantroles of fungi in naturalsystems. Explain why the mutualistic relationshipbetween plants and fungi was vital to the movementof both groupsonto land. 17.16 Describethe main traitsof fungi. 17.17 Describethe most coilrmonlife cycle of fungi. 17.18 Describethe sffuctureand characteristics of lichens. 17.19 Explain how parasiticfungi harmplants and animals. 17.20 Describethe positiveecological and practical roles of fungi. 161 162 Instructor's Guide to Text and Media KeyTerms mycorrhiza seed anther kingdomPlantae spore carpel cuticle pollination stigma stoma gymnospenn ovary vasculartissue angiosperm fruit xylem alternationofgenerations kingdomFungi phloem fossil fuel absorption gametangium conifer hypha embryophyte ovule mycelium charophycean pollen grain dikaryoticphase sporangium sepal fruiting body bryophyte petal mating type vascularplant stamen lichen Word Roots bryo- : moss;-phyte : plant (bryophytes.'the mosses,liverworts, and hornworts;a groupof nonvascu- lar plants that inhabitthe land but lack many of the terrestrialadaptations of vascularplants) di- : two; -karyo = nucleus(dil<nryotic: a myceliumwith two haploid nuclei per cell, one from each parent) Srmno- : naked;-sperm : seed(gymnosperm.' a vascularplant that bearsnaked seeds not enclosedin any specializedchambers) LectureOutline Introduction Plantsand Fungi-A Beneficial Partnership A. The lives of modern plants and fungi are intertwined. 1. We dependon plants and, indirectly, fungi for much of our food. 2. Plants are often harmedby fungi. 3. On the other hand, mycorrhizal fungi aid nearly all plants in the wild. Mycorrhizae are rootlike structuresmade of both fungi and plants. The fungi help plants obtain nutrients and water, and protect plant roots from parasites,in exchangefor food the plantsmake by photosynthesis(Figure 17.0). Preview:Mycorrhizae are also discussedin Module 32.11. 4. Modern agriculturalpractices, such as killing the parasiticfungi with fungicides, may disrupt mycorrhizal fungi, forcing the need for fertilizer. 5. Preview:This kind of dilemmaoften resultswhen humanstry to manipulatecom- plex naturalsystems (Chapter 38). B. Plantsand fungi evolved togetheras life movedonto land over 400 million years ago (mya).This observationis supportedby the earliestplant fossilshaving mycorrhizae. Chapter 17 Plants, Fungi, and the Colonization of l^and t63 Module 17.1 What is a plant? A. Review:In the two-kingdomsystem, Linnaeus classified algae as plants.In the five- kingdom system,algae are protists (Modules 15.14and 16.25). B. The definitionof plantsas multicellular,eukaryotic photosynthesizers also describes multicellular algae(Modules 16.23 and 16.24). C. Multicellular seaweeds,the most complex algae,are adaptedfor life in water,while plants are adaptedfor life on land (Figure L7.lA). For the former,the resources,includ- ing water,carbon dioxide, and minerals,are in direct contactwith their tissues,and wasteproducts can be washedaway. Water supportsand suspendsthe body of the alga. Holdfasts anchor the alga, and all other parts can be photosynthetic.Water provides a meansof dispersalfor gametesand offspring. D. Life on land imposesproblems. Water and nutrients are concentratedin the ground, while carbondioxide and light are most abundantabove the ground.Air provides no support againstthe force of gravity and will dry out reproductivecells. E. Adaptationsto a tenestrialenvironment in plants include the following: l. Discreteorgans: roots, stems,leaves, and gametangiaspecialized for anchorageand absorption,support, photosynthesis, and reproduction,respectively. 2. Mycorrhizalfungi to increasethe efficiency of absorptionof their roots. 3. A vascularnetwork to move food (phloem) and water (xylem) amongthe pans (Figure17.1B). 4. A cuticle on leavesand stemsto help retain water. 5. Dependencyon wind or animalcarriers to dispersemale gametes(contained in pollen) and offspring. 6. Offspring are kept moist by developing within the female gametangium. I. Plant Evolution and Divercity Module 17.2 Plantsevolved from greenalgae called charophyceans' A. Plants and green algaehave a number of homologousfeatures, such as identical photo- syntheticpigments, food storagemolecules, cell walls, and mechanismsof cell division (Modules 16.23and 16.24\. B. Plants may have evolvedfrom greenalgae about 500 mya. The ancestoris not known, but analysisof nucleic acid sequences,cell structure, and biochemistryindicate that a group of greenalgae, the charophyceans(Figure 17.2A,a simplecharophycean), and plants shareda commonancestor (Figure 17.2B.,a complexcharophycean.) C. Early plantsthrived on moist shorelineswhere spacewas essentiallylimitless, sunlight was abundant,and where there may not have been any herbivorousanimals. D. Among the earliestplant fossils is Coolcsonia,which have been found in strata datedto 408 mya. This plant had branched,upright, photosyntheticstems and sporesacs (spo- rangia) but lacked leaves(Figure 17.2C). E. Plants more complex than Cooksoniaare known to have been abundant=400 mya. Like Coolcsoniathey lacked leaves,but they had more complex sporangiaand were more firmly anchoredto the soil. F. A large numberand diversityof plantswith well-developedleaves and roots were pres- ent by 375 mya. t@ Instructor'sGuide to Textand Media Module L7.3 Plant diversityprovides clues to the evolutionaryhistory of the plant kingdom. A. Plant phylogeny showsbranching of severalplant lineages,reflecting major evolutionary steps.These are previewedhere, and detailsare addedin the modulesthat follow (Figure 17.3A). B. Two lineagesof plants arose,most likely from charophyceans,=400 mya. One of these lineagesgave rise to modernbryophytes. The otherlineage gave rise to vascularplants. C. Like other plants, bryophytes have a cuticle and embryosthat develop within gametan- gia. However,many bryophyteslack vasculartissue for waterconduction and internal support.Like their algal ancestors,bryophytes have flagellated spenn and dependon water for reproduction(Figure 17.38). D. Vascular plants have xylem and phloem that transportwater and nutrients and provide support (Figure 17.3C).In addition,these plants have embryonic development within gametangia. E. About 360 mya, vascularplants split into two lineages.One of theselineages gave rise to seedlessplants and the other gaverise to seedplants. Ferns are a modern exampleof a seedlessvascular plant and use a haploid spore for reproduction. The leaves(fronds) developfrom stemsthat grow along the ground (Figure 17.3C).Ferns are found in shadytemperate forests and are most diverse in the tropics. G. Seedplants makeup =90Voof all living plant species.Adaptations responsible for the successof this group include seedsthat provide the embryonicplant with a protective coating and a food supply.These plants also produce pollen, vehicles that transfernon- flagellated spenn to the female parts of plants. H. The earliest seedplants to appearwere the gJrmnosperms(naked seed). The nameof theseplants is basedon their seedsnot beingcontained within a fruit. Gymnosperms, along with seedlessplants, were dominantfor over 200 million years.The largestliving group of gymnospermsare the conifers. L Flowering plants (angiosperms) evolvedfrom the seedplant line =130 mya. Flowers increasethe efficiency of pollination and developinto fruils that protect seedsand increasethe efficiencyof seeddispersal. The majority of modernplant speciesare angiosperms. Preview: Angiospermsffucture is discussedin detail in Chapter31. II. Alternation of Generations and Plant Life Cycles Module 17.4 Haploid and diploid generationsalternate in plant life cycles. A. Review: Ulva hfe cycle (Figure 16.24C);human life cycle(Figure 8.13). B. Plant life cyclesalternate between multicellular, diploid (2n) andhaploid (1n) adults, unlike animals that are diploid as adults and producesingle-celled haploid gametes (Figure 17.4). c. Sporophytesgrow from diploid zygotesand producespores by meiosis. D. Gametophytesgrow from haploid sporesand producegametes by mitosis. E. Alternation of generations provides two chancesto producelarge numbersof offspring, zygotes,and spores. F. Major changesfrom the algal
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