2 Learning Objective 1What are some environmental challenges of living on land?How do some plant adaptations meet these challenges?
3 Colonization of Land by Plants Required anatomical, physiological, and reproductive adaptationsWaxy cuticleprotects against water lossStomatafor gas exchange needed for photosynthesis
4 Alternation of Generations 1 2 parts of plant life cyclehaploid gametophyte generationdiploid sporophyte generationGametophyte plantproduces gametes by mitosisgametes fuse (fertilization) to form zygote (first stage of sporophyte generation)
6 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION SporeSpermEggHAPLOID (n) GAMETOPHYTE GENERATIONMeiosisFertilizationDIPLOID (2n) SPOROPHYTE GENERATIONFigure 27.2: The basic plant life cycle.Plants have an alternation of generations, spending part of the cycle in a haploid gametophyte stage and part in a diploid sporophyte stage. Depending on the plant group, the haploid or the diploid stage may be greatly reduced.ZygoteEmbryoSporophyteFig. 27-2, p. 582
7 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION SpermEggFertilizationSporeMeiosisDIPLOID (2n) SPOROPHYTE GENERATIONSporophyteZygoteEmbryoFigure 27.2: The basic plant life cycle.Plants have an alternation of generations, spending part of the cycle in a haploid gametophyte stage and part in a diploid sporophyte stage. Depending on the plant group, the haploid or the diploid stage may be greatly reduced.Stepped ArtFig. 27-2, p. 582
8 Alternation of Generations 2 Zygote develops into multicellular embryoprotected and nourished by gametophyteMature sporophyte plantdevelops from the embryoproduces sporogenous cells (spore mother cells)
9 Alternation of Generations 3 Sporogenous cells undergo meiosis to form sporesfirst stage in gametophyte generation
10 KEY CONCEPTSPlants undergo an alternation of generations between multicellular gametophyte and sporophyte generations
11 Gametangia 1 Most plants have multicellular gametangia with protective jacket of sterile cells surrounding gametes
12 Gametangia 2 Antheridia Archegonia gametangia that produce sperm cells gametangia that produce eggs
14 Developing sperm cells Sterile cellsAntheridiumFigure 27.3: Plant gametangia.Shown are generalized moss gametangia.Fig. 27-3a, p. 583
15 Egg Archegonium Sterile cells Fig. 27-3b, p. 583 Figure 27.3: Plant gametangia.Shown are generalized moss gametangia.Fig. 27-3b, p. 583
16 Vascular Transport System In ferns and other vascular plantsxylem conducts water and dissolved mineralsphloem conducts dissolved sugar
17 KEY CONCEPTSAdaptations to life on land that have evolved in plants include a waxy cuticle to prevent water loss; multicellular gametangia; stomata; and for most plants, vascular tissues containing lignin
18 Learning Objective 2From which green algal group are plants hypothesized to have descended?Describe supporting evidence
19 Charophytes Plants probably arose from charophytes a group of green algaeBased on molecular comparisons of DNA and RNA sequencesclose match between charophytes and plants
21 NONVASCULAR BRYOPHYTES VASCULAR SEEDLESS PLANTS VASCULAR SEED PLANTSGymnospermsClub mossesAngiospermsHornwortsLiverwortsMossesFernsEvolution of seedsFigure 27.4: Plant evolution.Cladograms such as this one represent an emerging consensus that is open to change as new discoveries are made. Although the arrangement of nonvascular, seedless vascular, and seed plant groupings is widely recognized, the order in which the hornworts, liverworts, and mosses evolved is not yet resolved.Evolution of dominant sporophyte, vascular tissueEvolution of cuticle, multicellular gametangia, multicellular embryosGreen algal ancestorFig. 27-4, p. 584
22 KEY CONCEPTSBiologists infer that plants evolved from aquatic green algal ancestors known as a charophytes
23 Insert “Evolutionary tree for plants” plant_tree_v2.swf
24 Explore plant evolution by clicking on the figure in ThomsonNOW.
25 Learning Objective 3What features distinguish bryophytes from other plants?
26 Bryophytes Nonvascular (lack xylem and phloem) unlike other land plantsDominant gametophyte generationunlike other plantsSporophytes remain permanently attachednutritionally dependent on gametophytes
27 Learning Objective 4What are the three phyla of bryophytes?
28 Mosses (Phylum Bryophyta) Gametophytes are green plants that grow from a filamentous protonema
29 Liverworts (Phylum Hepatophyta) Many gametophytes are flattened, lobelike thalli (others are leafy)
30 Hornworts (Phylum Anthocerophyta) Have thalloid gametophytes
31 Fig. 27-5, p. 585 Figure 27.4: Plant evolution. Cladograms such as this one represent an emerging consensus that is open to change as new discoveries are made. Although the arrangement of nonvascular, seedless vascular, and seed plant groupings is widely recognized, the order in which the hornworts, liverworts, and mosses evolved is not yet resolved.Fig. 27-5, p. 585
32 Nonvascular bryophytes seed plants Vascular seedless plantsVascularNonvascular bryophytesseed plantsVascularFigure 27.4: Plant evolution.Cladograms such as this one represent an emerging consensus that is open to change as new discoveries are made. Although the arrangement of nonvascular, seedless vascular, and seed plant groupings is widely recognized, the order in which the hornworts, liverworts, and mosses evolved is not yet resolved.Green algal ancestorFig (1), p. 585
33 KEY CONCEPTSMosses and other bryophytes lack vascular tissues and do not form true roots, stems, or leaves
34 Learning Objective 5 Describe the life cycle of mosses Compare their gametophyte and sporophyte generations
35 Mosses 1 Green moss gametophyte Fertilization bears archegonia / antheridia at top of plantFertilizationsperm cell fuses with egg cell in archegonium (zygote)
36 Mosses 2 Zygote grows into embryo develops into moss sporophyte attached to gametophyte
37 Mosses 3 Meiosis When spore germinates occurs within capsule of sporophyteproduces sporesWhen spore germinatesgrows into a protonemaforms buds that develop into gametophytes
39 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION Antheridia at the tip of the gametophyte shootGametophyte plantsBuds on protonema1Antheridia with sperm cellsSpore germinatesSpores released6ProtonemaSperm cellHAPLOID (n) GAMETOPHYTE GENERATIONArchegonium with egg2MeiosisFertilizationDIPLOID (2n) SPOROPHYTE GENERATION5Figure 27.6: The life cycle of mosses.The gametophyte generation is dominant in the moss life cycle. After sexual reproduction, the sporophyte grows out of the gametophyte. See text for a detailed description.CalyptraZygoteCapsule4Sporogenous cells that undergo meiosis3SporophyteEmbryoGametophyte plantFig. 27-6, p. 586
41 Capsule Seta Foot Fig. 27-7, p. 587 Figure 27.7: Moss sporophytes. Each consisting of a foot, seta, and capsule, the sporophytes grow out of the top of the gametophytes. Spores are produced within the capsule. Shown is the haircap moss (Polytrichum commune).Fig. 27-7, p. 587
43 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION AntheridiophoreArchegoniophoreMale thallusGermination of spores and development of young gametophyte1Female thallusAntheridia with sperm cells5Gemmae cupSpores releasedSperm cellMale and female gametophyte plantsHAPLOID (n) GAMETOPHYTE GENERATIONArchegonia with eggs2FertilizationMeiosisDIPLOID (2n) SPOROPHYTE GENERATION4FootFigure 27.8: The life cycle of the common liverwort (Marchantia polymorpha).The dominant generation is the gametophyte, represented by separate male and female thalli. The stalked, umbrella-shaped structures are the antheridiophores, with antheridia that produce sperm cells, and the archegoniophores, with archegonia that each bear an egg cell. See text for a detailed description.SetaZygoteTissue derived from archegoniumCapsuleEmbryoSporogenous cells that undergo meiosis3SporophyteFig. 27-8, p. 588
44 Insert “Moss life cycle” moss_life_cycle_v2.swf
46 Watch the life cycles of the mosses and liverworts by clicking on the figures in ThomsonNOW.
47 Learning Objective 6What features distinguish seedless vascular plants from algae and bryophytes?
48 Seedless Vascular Plants Have adaptations that algae and bryophytes lackvascular tissuesdominant sporophyte generationReproduction depends on wateras transport medium for motile sperm cells (as in bryophytes)
49 Learning Objective 7What are the two phyla of seedless vascular plants?
50 Club Mosses (Phylum Lycopodiophyta) Sporophytes consist of roots, rhizomes, erect branches, and microphylls (leaves)
51 Vascular supply to enation Microphyll (one vein) StemMicrophyllVascular tissueEnationVeinSmooth stemEnationVascular supply to enationMicrophyll (one vein)Figure 27.10: Evolution of microphylls and megaphylls.Dichotomous branching (in b) is branching into two equal halves. Webbing (in b) is the evolutionary process in which the spaces between close branches become filled with chlorophyll-containing cells.Fig a, p. 590
53 Green algal ancestor Vascular seedless plants Nonvascular bryophytes Vascular seed plantsFigure 27.11: Club mosses.(a, Redrawn from M. Hirmer, Handbuch der Paläobotanik, R. Olderbourg, Munich, 1927.)Green algal ancestorFig (1), p. 591
54 Strobilus Leaves (microphylls) Fig. 27-11 (a-b), p. 591 Figure 27.11: Club mosses.(a, Redrawn from M. Hirmer, Handbuch der Paläobotanik, R. Olderbourg, Munich, 1927.)Fig (a-b), p. 591
55 Ferns (Phylum Pteridophyta) Largest and most diverse group of seedless vascular plantsFern sporophyte consists of a rhizome that bears fronds and true rootsIncludes whisk ferns and horsetails
62 Underside of enlarged mature gametophyte (prothallus) Germination of spores and development of young gametophyteEgg45ArchegoniumSpores releasedRhizoids3AntheridiumSporangiumHAPLOID (n) GAMETOPHYTE GENERATIONSperm cellMeiosisFertilizationCells within sporangia undergo meiosisDIPLOID (2n) SPOROPHYTE GENERATIONSorus (cluster of sporangia)Zygote26Figure 27.13: The life cycle of ferns.Note the clearly defined alternation of generations between the gametophyte (prothallus) and sporophyte (leafy plant) generations. See text for a detailed description.Frond1Leaf of young sporophyteDevelopment of the sporophyteLeaf cross sectionHaploid prothallusFiddleheadRoot of young sporophyteRootsRhizomeUnderside of a frondFern (mature sporophyte)Fig , p. 593
63 Whisk FernsSporophytes have dichotomously branching rhizomes and erect stemslack true roots and leaves
64 Vascular seedless plants Nonvascular bryophytes Vascular seed plants Figure 27.14: The sporophyte of Psilotum nudum, a whisk fern.The stem is the main organ of photosynthesis in this rootless, leafless, vascular plant. Sporangia, which are initially green but turn yellow as they mature, are borne on short lateral branches directly on the stems.Green algal ancestorFig a, p. 594
65 Aerial stem with scalelike outgrowths SporangiaAerial stem with scalelike outgrowths(no leaves)Figure 27.14: The sporophyte of Psilotum nudum, a whisk fern.The stem is the main organ of photosynthesis in this rootless, leafless, vascular plant. Sporangia, which are initially green but turn yellow as they mature, are borne on short lateral branches directly on the stems.Fig b, p. 594
66 Horsetails Sporophytes have hollow, jointed roots, rhizomes, aerial stemsleaves reduced to megaphylls
67 Dichotomous end branches Thicker main stemDichotomous end branchesEqual branchesVascular tissueThinner side branchFigure 27.10: Evolution of microphylls and megaphylls.Dichotomous branching (in b) is branching into two equal halves. Webbing (in b) is the evolutionary process in which the spaces between close branches become filled with chlorophyll-containing cells.Dichotomously branching stemsOvertopping(unequal branching)Planation (branching in same plane)Webbing of side branch systemMegaphyll (many veins)Fig b, p. 590
69 Nonvascular bryophytes seedless plants Vascular Vascular seed plants Green algal ancestorFigure 27.15: Horsetails.(a, Redrawn from L. Emberger, Les Plantes Fossiles, Masson et Cie, Paris, 1968.)Fig a, p. 594
70 Strobilus Vegetative shoots Reproductive shoots Fig. 27-15b, p. 594 Figure 27.15: Horsetails.(a, Redrawn from L. Emberger, Les Plantes Fossiles, Masson et Cie, Paris, 1968.)Reproductive shootsFig b, p. 594
72 KEY CONCEPTSIn club mosses and ferns, lignin-hardened vascular tissues that transport water and dissolved substances throughout the plant body have evolved
73 Learning Objective 8 Describe the life cycle of ferns Compare sporophyte and gametophyte generations
74 Fern Sporophytes Roots, rhizomes, leaves are megaphylls Leaves (fronds) bear sporangia in clusters (sori)Meiosis in sporangia produces haploid spores
75 Fern Gametophyte Fern Gametophyte (prothallus) develops from haploid sporebears both archegonia and antheridia
76 Insert “Fern life cycle” fern_life_cycle_v2.swf
77 Watch the life cycle of the ferns by clicking on the figure in ThomsonNOW.
78 Learning Objective 9What is the difference between the generalized life cycles of homosporous and heterosporous plants?
79 Homospory Production of one kind of spore in bryophytes, most club mosses, most ferns including whisk ferns and horsetailsSpores give rise to gametophyte plantsproduce both egg cells and sperm cells
80 Heterospory 1Production of two kinds of spores (microspores and megaspores)in some club mosses and fernsin all seed plants
82 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION MegasporeGametophyteArchegoniumMicrosporeAntheridiumHAPLOID (n) GAMETOPHYTE GENERATIONSpermEggMeiosisFertilizationDIPLOID (2n) SPOROPHYTE GENERATIONMicrosporocyteFigure 27.16: The basic life cycle of heterosporous plants.Two types of spores, microspores and megaspores, are produced during the life cycle of heterosporous plants.ZygoteMegasporocyteMicrosporangiumEmbryoMegasporangiumSporophyteFig , p. 595
83 Heterospory 2 Microspores Megaspores give rise to male gametophytes that produce sperm cellsMegasporesgive rise to female gametophytes that produce eggs
85 HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION Male gametophyte develops inside microspore wallSingle antheridium in male gametophyte produces many sperm cells3Ruptured megaspore wallMicrospores5Sperm cellArchegonium containing eggFemale gametophyte develops and protrudes from megaspore wall4Longitudinal section through archegoniumMegasporesHAPLOID (n) GAMETOPHYTE GENERATIONEggMeiosisFertilizationMicrosporangiumwith microsporocytesDIPLOID (2n) SPOROPHYTE GENERATIONFigure 27.17: The life cycle of spike moss (Selaginella).Spike moss is heterosporous, producing two types of spores in one strobilus. The megaspores develop into female gametophytes, and the microspores become male gametophytes. See text for a detailed description.Megasporangium with megasporocyteFemale gametophyteStrobilusFirst leaves1Leaf (microphyll)StemZygoteStemLongitudinal section through strobilus6RootRootYoung sporophyte (attached to female gametophyte)Mature sporophyteFig , p. 596
86 Evolution of Heterospory Essential step in evolution of seedsRhyniaAglaophyton