The Plant Kingdom:Seedless Plants Chapter 27
Learning Objective 1 • What are some environmental challenges of living on land? • How do some plant adaptations meet these challenges?
Colonization of Land by Plants • Required anatomical, physiological, and reproductive adaptations • Waxy cuticle • protects against water loss • Stomata • for gas exchange needed for photosynthesis
Alternation of Generations1 • 2 parts of plant life cycle • haploid gametophyte generation • diploid sporophyte generation • Gametophyte plant • produces gametes by mitosis • gametes fuse (fertilization) to form zygote (first stage of sporophyte generation)
Gametophyte Spore Sperm Egg HAPLOID (n) GAMETOPHYTE GENERATION Meiosis Fertilization DIPLOID (2n) SPOROPHYTE GENERATION Zygote Embryo Sporophyte Fig. 27-2, p. 582
Gametophyte Spore Sperm Egg HAPLOID (n) GAMETOPHYTE GENERATION Meiosis Fertilization DIPLOID (2n) SPOROPHYTE GENERATION Zygote Embryo Sporophyte Stepped Art Fig. 27-2, p. 582
Alternation of Generations2 • Zygote develops into multicellular embryo • protected and nourished by gametophyte • Mature sporophyte plant • develops from the embryo • produces sporogenous cells (spore mother cells)
Alternation of Generations3 • Sporogenous cells undergo meiosis to form spores • first stage in gametophyte generation
KEY CONCEPTS • Plants undergo an alternation of generations between multicellular gametophyte and sporophyte generations
Gametangia 1 • Most plants have multicellular gametangia • with protective jacket of sterile cells surrounding gametes
Gametangia 2 • Antheridia • gametangia that produce sperm cells • Archegonia • gametangia that produce eggs
Developing sperm cells Sterile cells Antheridium Fig. 27-3a, p. 583
Egg Archegonium Sterile cells Fig. 27-3b, p. 583
Vascular Transport System • In ferns and other vascular plants • xylem conducts water and dissolved minerals • phloem conducts dissolved sugar
KEY CONCEPTS • Adaptations 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
Learning Objective 2 • From which green algal group are plants hypothesized to have descended? • Describe supporting evidence
Charophytes • Plants probably arose from charophytes • a group of green algae • Based on molecular comparisons of DNA and RNA sequences • close match between charophytes and plants
VASCULAR SEEDLESS PLANTS NONVASCULAR BRYOPHYTES VASCULAR SEED PLANTS Gymnosperms Angiosperms Club mosses Hornworts Liverworts Mosses Ferns Evolution of seeds Evolution of dominant sporophyte, vascular tissue Evolution of cuticle, multicellular gametangia, multicellular embryos Green algal ancestor Fig. 27-4, p. 584
KEY CONCEPTS • Biologists infer that plants evolved from aquatic green algal ancestors known as a charophytes
Insert “Evolutionary tree for plants” plant_tree_v2.swf
Learning Objective 3 • What features distinguish bryophytes from other plants?
Bryophytes • Nonvascular (lack xylem and phloem) • unlike other land plants • Dominant gametophyte generation • unlike other plants • Sporophytes remain permanently attached • nutritionally dependent on gametophytes
Learning Objective 4 • What are the three phyla of bryophytes?
Mosses (Phylum Bryophyta) • Gametophytes are green plants that grow from a filamentous protonema
Liverworts (Phylum Hepatophyta) • Many gametophytes are flattened, lobelike thalli (others are leafy)
Hornworts(Phylum Anthocerophyta) • Have thalloid gametophytes
Vascular seedless plants Nonvascular bryophytes Vascular seed plants Green algal ancestor Fig. 27-5 (1), p. 585
KEY CONCEPTS • Mosses and other bryophytes lack vascular tissues and do not form true roots, stems, or leaves
Learning Objective 5 • Describe the life cycle of mosses • Compare their gametophyte and sporophyte generations
Mosses 1 • Green moss gametophyte • bears archegonia / antheridia at top of plant • Fertilization • sperm cell fuses with egg cell in archegonium (zygote)
Mosses 2 • Zygote • grows into embryo • develops into moss sporophyte attached to gametophyte
Mosses 3 • Meiosis • occurs within capsule of sporophyte • produces spores • When spore germinates • grows into a protonema • forms buds that develop into gametophytes
Antheridia at the tip of the gametophyte shoot Gametophyte plants Buds on protonema 1 Antheridia with sperm cells Spore germinates Spores released 6 Protonema Sperm cell HAPLOID (n) GAMETOPHYTE GENERATION 2 Archegonium with egg Fertilization Meiosis DIPLOID (2n) SPOROPHYTE GENERATION 5 Calyptra Zygote Capsule 4 3 Sporogenous cells that undergo meiosis Sporophyte Embryo Gametophyte plant Fig. 27-6, p. 586
Capsule Seta Foot Fig. 27-7, p. 587
Antheridiophore Archegoniophore Male thallus Germination of spores and development of young gametophyte 1 Antheridia with sperm cells Female thallus 5 Gemmae cup Spores released Sperm cell Male and female gametophyte plants HAPLOID (n) GAMETOPHYTE GENERATION Archegonia with eggs 2 Fertilization Meiosis DIPLOID (2n) SPOROPHYTE GENERATION 4 Foot Seta Zygote Tissue derived from archegonium Embryo Capsule Sporogenous cells that undergo meiosis 3 Sporophyte Fig. 27-8, p. 588
Insert “Moss life cycle” moss_life_cycle_v2.swf
Insert “Marchantia, a liverwort” liverwort.swf
Watch the life cycles of the mosses and liverworts by clicking on the figures in ThomsonNOW.
Learning Objective 6 • What features distinguish seedless vascular plants from algae and bryophytes?
Seedless Vascular Plants • Have adaptations that algae and bryophytes lack • vascular tissues • dominant sporophyte generation • Reproduction depends on water • as transport medium for motile sperm cells (as in bryophytes)
Learning Objective 7 • What are the two phyla of seedless vascular plants?
Club Mosses (Phylum Lycopodiophyta) • Sporophytes consist of roots, rhizomes, erect branches, and microphylls (leaves)