acellular slime mold 1 cellular slime mold CHAPTER 29 Plant Diversity I How plants colonized land Land plants evolved from green algae Charophytes have been identified as the closest relatives of land plants 2 Shared characteristics include cellulose synthesizing protein complexes see fig 29 2 peroxisome enzymes structure of flagellated sperm formation of phragmatoplasts preceding cell plate formation The charophytes and plant share some common traits however there are some major differences The algae traits include Most or all of life cycle in water tidal forms No vascular tissue No leaves stomata or cuticle Variation in dominant form of the life cycle o In some sporophyte is dominant o In some gametophyte is dominant Sporophyte and gametophyte can be heteromorphic or isomorphic o Heteromorphic referring to a condition in the life cycle of plants and certain algae in which the sporophyte and gametophyte generations differ in morphology o Isomorphic referring to alternating generations in plants and certain algae in which the sporophytes and gametophytes look alike although they differ in chromosome number There are four derived trait which appear in some maybe most land plants Alternation of generations and multicellular dependent embryos Apical meristems plant tissue that remains embryonic as long as the plant lives allowing for indeterminate growth Walled spores produced in sporangia Multicellular gametangia Most plants go through a life cycle that involves an alternation of generations see fig 13 6b In this life cycle the diploid phase produces a sporophyte spore producing plant that produces haploid spores by meiosis The spores grow into the gametophyte multicellular haploid from that produces haploid gametes by mitosis The haploid gametes unite and develop into sporophytes that produces gametes These gametes fuse during fertilization to form a diploid zygote that then grows into another sporophyte 3 In addition to the characteristics noted above the plant kingdom shows a range of traits that appeared as plants made the transition from their origins in water onto the land Some of these new traits are Anchoring mechanism Conducting vessels Increased support mechanism External protection Mechanism for gas exchange Roots Phloem Xylem and Lignin Cuticle Stomata Xylem and Phloem are parts of the plants vascular tissue system a transport system formed by xylem and phloem throughout a vascular plant Xylem transports water and minerals phloem transports sugars the products of photosynthesis They are vessels that transport water minerals nutrients especially sugars and hormones throughout the plant Plants with this trait are vascular plants plant with vascular tissue include all living plant species except liverworts mosses and hornworts Lignin is a material that is added to the cell walls of woody plants It 4 increases the stiffness of the cells and allows better support for the leaves It is a hard material embedded in the cellulose matrix of vascular plant cell walls that provides structural support in terrestrial species Cuticle is a layer of waxy material on the epidermal layer of plants that helps prevent water loss or desiccation Stomata stoma singular are openings in the surface usually underside of a leaf which allow gas exchange but limit water loss As plants moved to land two main categories of land plants arose see table 29 1 Nonvascular Bryophytes Vascular Tracheophytes The evolution to land provide advantages Sunlight unfiltered by water and plankton More abundant CO2 Higher concentration of nutrients in soil Great opportunity for adaptive radiation Few herbivores and pathogens Nonvascular Plants The nonvascular plants did not develop all of the characteristics required for a complete terrestrial existence and therefore remain closely linked to water No vascular tissue No true root but they have rhiziods a long tubular single cell or filament of cells that anchors bryophytes to the ground Unlike roots rhizoids are not composed of tissues lack specialized conducting cells and do not play a primary role in water and mineral absorption No true stems or true leaves Semi aquatic freshwater Require water for sexual reproduction Cuticle in some moss species and stomata in some hornwort and moss sporophytes Protective structure for gametes o Archegonium the female gametanguim a moist chamber in which gametes develop and antheridium the male gametangium a moist chamber in which gametes develop Since these plants lack vascular tissue they rely on diffusion to move water nutrients etc This limits their size and where they can grow 5 Three of the Divisions of nonvascular plants are see table 29 1 Liverworts small herbaceous nonvascular plant that is a member of the phylum Hepatophyta Hornworts a small herbaceous nonvascular plant that is a member of the Mosses a small herbaceous nonvascular plant that is a member of the phylum Anthocerotophyta phylum Bryophyta In all three bryophyte phyla gametophytes are the dominant stage of the life cycle During the haploid phase of the life cycle the gametophytes produce archegonia singular archegonium and antheridia singular antheridium see fig 29 8 These structures produce and protect the gametes until mating During mating the sperm swim or are splashed from the antheridia to the archegonia Bryophyte sporophytes grow from the zygote directly out of the gametophyte archegonium The sporophyte has a Foot the portion of a bryophyte sporophyte that gathers sugars amino acids water and minerals from parent gametophyte via transfer cells Seta elongated stalk of a bryophyte sporophyte Capsule the sporangium of a bryophyte moss liverwort or hornwort The remaining main category of land plants the vascular plants shows additional characteristics Vascular tissue o Xylem and Phloem Roots Leaves Lignin Vascular plants have 2 types of vascular tissue Xylem conducts most of the water and minerals upward Phloem distributes sugars amino acids and other organic products in 6 varying directions Roots Leaves Anchor vascular plants Absorb water and nutrients from the soil Increase surface area for capturing more sunlight The first vascular plants to evolve were the seedless vascular plants see fig 29 13 Recognize the groups like non vascular plants and seedless vascular plant while they share common features are not clades The term used to refer to these groups is grade Grade The seedless vascular plants share some common characteristics Produce spores not seeds
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