Chapter 29 Life plants enabled other life forms to survive on land Plants supply oxygen and ultimately end up as food They also create habitats by stabilizing soil 29 1 LAND PLANTS EVOLVED FROM GREEN ALGAE MORPHOLGOICAL AND MOLECULAR EVIDENCE Chorophytes are said to said to be the closest living relatives due to Rings of Cellulose synthesizing proteins o Both Plants and Chorophytes have distinctive circular rings of protein in plasma membrane Structure of flagellated sperm resemble each other Formation of a phragmoplast o A group of microtubule s known as phragmoplast forms between daughter nuclei of dividing cell A cell plate then develops in the middle of phragmoplast in the dividing cell and gives rise to new cross wall that separates daughter cells Studies from nuclear and chloroplast genes from a wide range of plants and algae indicate that that charophytes are the closest living relatives of land plants ADAPTATIONS ENABLING THE MOVE TO LAND Many carophyte algae live in shallow water that is prone to drying and as a result natural selection selected for a layer of durable polymer called SPOROPOLLENIN which prevents exposed zygotes from drying out The accumulation of such adaptations may have allowed plants to colonize land Land allowed for bright sunlight and more CO2 and nutrients However there was less water and lack of structural support Derived Traits of Plants A series of 5 traits that are found in land plants but not charophyte algae may have allowed them to live on dry land The epidermis in many species has a CUTICLE which is a waxy covering that prevents dehydration STOMATA are specialized pores that support photosynthesis by allowing CO2 and O2 to get exchanged Stomata also are the main avenue for evaporation and close when it is hot and dry Alternation of Generations All plants alternate between gametophytes and sprophytes life cycles This is found in all algae but not the algae closest to land plants charophytes GAMETOPHYTES are named for their production by mitosis of haploid gametes that fuse during fertilization forming diploid zygotes Mitosis of the zygote results in diploid sporophytes Meiosis in a sporophyte results in haploid cells that can develop into a new organism Diagram of 614 Multicellular Dependent Embryos Multicellular plant embryos develop from zygotes that are retained within the tissues of the female parent The parental tissues protect and provide nutrients to the embryo Specialized placental transfer cells enhance the transfer of nutrients to the embryo through plasma membrane and cell wall This has caused land plants to be called embryophytes Walled Spores Produced in Sporangia The polymer sporopollenin makes the walls of plant spores tough and resistant enabling them to be dispersed through dry air Sporangia is a multicellular organ that produces spores from sporocytes spore mother cells that undergo meiosis and produce haploid spores Sporangia that produce spores with sporopollenin enriched walls are key adaptations Charophytes produce spores but they lack sporangia and sporopollenin Multicellular Gametangia Gametangia multicellular organs that produced gametes separate plants from algal ancestors Female gametangia are called archegonia and produce a single non motile egg The male gametangia is called the antheridia and release sperm into environment Fertilization occurs in the archegonia Apical Meristems This helps expose plants to environmental resources These are regions of cell division a found in the tips of roots and shoots The cells produced can differentiate into outer epidermis other internal tissues and leaves This allows plants to grow in order to have regions under the soil for nutrients and water and above the ground for CO2 and light THE ORIGIN AND DIVERSIFICATION OF PLANTS The algae from which land plants evolved include many unicellular species and small colonial species What distinguishes spores of plants from the ones in algae and fungi is that they are different in chemical composition and the structure of the walls One way to distinguish groups of plants is whether or not they have an extensive system of vascular tissue a cell network that brings water and nutrients NONVASCULAR PLANTS are known as BRYOPHYTES but they do not form a monophyletic group VASCULAR PLANTS which form a clade can be broken into 2 smaller clades LYCOPHYTES AND MONILOPHYTES These two classes are seedless vascular plants but do not form a clade A group that that does not form a clade but has common biological features is called a GRADE A third clade of vascular plants consists of SEED PLANTS which have an embryo packed inside a protective coat This clade is broken into GYMNOSPERMS naked seeds AND ANGIOSPERMS flowering plants 27 3 MOSSES AND OTHER NONVASCULAR PLANTS HAVE LIFE CYCLES DOMINATED AND GAMETOPHYTES Nonvascular plants Bryophytes are broken into 3 phyla of small herbaceous plants LIVERWORTS MOSSES HORNWORTS Researchers believe that Bryophytes were the first to diverge from the common ancestor of land plants BRYOPHYTE GAMETOPHYTES Unlike the vascular plants in all 3 bryophyte phyla the haploid gametophytes are the dominant stage of the life cycle Sporophytes are only there for a short period Moss spores produce a mass of green branched one cell thick filaments known as protoema that aids in the absorption of water or minerals which help produce buds Each bud produces gamete producing gametophores The protonema and gametophores make the body of the moss gametophytes Due to thin body parts and lack of a vascular system Bryophyte gametophytes form tree hugging carpets which are very thin Delicate rhizoids not composed of tissues lack specialized conducting cells and anchor gametophytes In addition Gametophytes can form multiple gametangia each of which produce gametes and is protected by a tissue Each archegonium produces an egg while antheridium produces many sperm Bryophyte sperm need water to swim and as a result many bryophyte species are found in moist environments BRYOPHYTE SPOROPHYTES Cells contain green plastids and photosynthetic when sporophytes are young A sporophyte cannot live independently and remains attached to the gametophyte Embedded in the archegonium the foot absorbs nutrients from the gametophyte the seta stalk conducts materials to the sporangium capsule which uses them to produce spores by meiosis Bryophyte sporophytes can produce enormous numbers of spores The upper part of the capsule known as the peristome features a