(acellular slime mold) (cellular slime mold )CHAPTER 29: PlantDiversity I: How plants colonized land- Land plants evolved from greenalgae- Charophytes have been identifiedas the closest relatives of landplants1Shared characteristics include:- cellulose synthesizing protein complexes (see fig 29.2)- peroxisome enzymes- structure of flagellated sperm- formation of phragmatoplasts preceding cell plate formationThe 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 cycleo In some sporophyte is dominant o In some gametophyte is dominant- Sporophyte and gametophyte can be heteromorphic or isomorphico Heteromorphic: referring to a condition in the life cycle of plants and certain algae in which the sporophyte and gametophyte generations differ in morphologyo Isomorphic: referring to alternating generations in plants and certain algae in which the sporophytes and gametophytes look alike, although they differ in chromosome numberThere 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 gametangiaMost 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.2The 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. 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 Roots Conducting vessels Xylem and Phloem Increased support mechanism Lignin External protection Cuticle Mechanism for gas exchange 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 3increases 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 helpsprevent water loss or desiccation.- Stomata (stoma singular) are openings in the surface (usually underside) ofa leaf, which allow gas exchange but limit water loss. As plants moved to land two main categoriesof land plants arose (see table 29.1): - Nonvascular - Bryophytes- Vascular - TracheophytesThe evolution to land provide advantages- Sunlight unfiltered by water andplankton- More abundant CO2- Higher concentration of nutrients in soil- Few herbivores and pathogens- Great opportunity for adaptive radiationNonvascular PlantsThe nonvascular plants did not develop all ofthe characteristics required for a completeterrestrial existence and therefore remainclosely linked to water.- No vascular tissue- No true root but they have rhiziods (along, tubular single cell or filament ofcells that anchors bryophytes to theground. 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 gameteso 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.4Three 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 phylum Anthocerotophyta- Mosses: : a small herbaceous, nonvascular plant that is a member of the phylum BryophytaIn 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 andprotect the gametes untilmating. During mating, thesperm swim (or are splashed)from the antheridia to thearchegonia.Bryophyte sporophytes growfrom the zygote directly outof the gametophytearchegonium.The sporophyte has a:- Foot (the portion of abryophyte sporophytethat gathers sugars,amino acids, water, andminerals from parentgametophyte via transfercells)- Seta (elongated stalk ofa bryophyte sporophyte)- Capsule (the sporangiumof a bryophyte, moss,liverwort, or hornwort)The remaining main category of land plants, the vascular plants, shows additional characteristics:- Vascular tissueo Xylem and Phloem- Roots - Leaves- LigninVascular plants have 2 types of vascular tissue5Xylem: conducts most of the water and minerals upwardPhloem: distributes sugars, amino acids, and other organic products in varying directionsRootsAnchor vascular plantsAbsorb water and nutrients from the soilLeavesIncrease surface area for capturing more sunlightThe first vascular plants to evolve were the seedless vascular
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