Chapter 29 Notes Plant Diversity I How Plants Colonized Land Land plants enabled other life forms to survive on earth Concept 29 1 Land Plants Evolved From Green Algae Green algae called charophytes are the closest relative of land plants MORPHOLOGICAL AND MOLECULAR EVIDENCE Plants have cell walls made of cellulose and so do green algae dinoflagellates and brown algae Present day algae share the following distinctive traits with land plants RINGS OF CELLULOSE SYNTHESIZING PROTEINS These rings synthesize the cellulose microfibrils of the cell wall In contrast noncharophyte algae have linear sets of proteins that synthesize cellulose STRUCTURE OF FLAGELLATED SPERM FORMATION OF A PHRAGMOPLAST A group of microtubules known as the phragmoplast forms between the daughter nuclei of a dividing cell A plate then develops in the middle of the phragmoplast across the midline of the dividing cell Cell plate gives rise to a cross wall that separates the daughter cells ADAPTATIONS ENABLING THE MOVE TO LAND In charophytes a layer of durable polymer called SPOROPOLLENIN prevents zygotes from drying out DERIVED TRAITS OF PLANTS CUTICLE the covering on the epidermis that consists of wax and other polymers preventing desiccation drying out also provides protection from microbial attack STOMATA main avenues by which water exits the plant In hot dry conditions stomata close minimalizing water loss Mycorrhizal fungi form extensive networks of filaments through the soil and transfer nutrients to their symbiotic plant partner THE ORIGIN AND DIVERSIFICATION OF PLANTS VASCULAR TISSUE cells joined into tubes that transport water and nutrients throughout the plant body NONVASCULAR PLANTS do not have an extensive transport system liverworts mosses and hornworts Informally called Bryophytes SEEDLESS VASCULAR PLANTS Lycocytes club mosses and their relatives Monilophytes ferns and their relatives SEED an embryo packaged with a supply of nutrients inside of a protective coat GYMNOSPERMS naked seed seeds that are not enclosed in chambers ANGIOSPERMS all flowering plants seeds develop inside chambers that originate in flowers Concept 29 2 Mosses and Other Nonvascular Plants have Life Cycles Dominated by Gametophytes Liverworts hornworts and mosses were the earliest lineages to have diverged from the common ancestor of land plants BRYOPHYTE GAMETOPHYTES Gametophytes are dominant stage of life cycle Usually larger and longer living than sporophytes Germinating moss spores characteristically produce a mass of green branched one cell thick filaments known as a PROTONEMA has a large surface area that enhances absorption of water and minerals Each budlike growth has an apical meristem that generates a gamete producing structure known as a GAMETOPHORE RHIZOIDS delicate long tubular single cell structures or filaments of cells that anchor gametophytes Rhizoids aren t composed of cells and they lack specialized conducting cells ARCHEGONIUM produces one egg ANTHERIDIUM produces many sperm In mosses these two are usually carried out on separate male and female gametophytes Flagellated sperm swim through water and enter the archegonia Eggs remain in archegonia BROOD BODIES small plantlets that detach from the parent plant and grow into new genetically identical copies of their parent BRYOPHYTE SPOROPHYTES Contain plastids that are usually green and photosynthetic when the sporophytes are young The two cannot live independently Sporophyte dependent on gametophyte Bryophytes have smallest sporophytes of all extant plants Typical bryophyte sporophyte consists of a foot a seta and a sporangium FOOT absorbs nutrients from gametophyte SETA or stalk conducts these materials to the sporangium or CAPSULE CAPSULE uses them to produce spores by meiosis PERISTOME a ring of interlocking tooth like structures featured at the upper part of the capsule teeth are open under dry conditions and are closed when it is moist Liverworts do NOT have stomata Feather moss Pleurozium harbor nitrogen fixing cyanobacteria that increase the availability of nitrogen in the ecosystem One wetland genus Sphagnum or peat moss is often a major component of partially decayed organic material known as PEAT Concept 29 3 Ferns and other Seedless Vascular Plants were the First Plants to Grow Tall Vascular plants dominate most of the landscapes today Sperm of ferns and all other seedless vascular plants are flagellated and swim through a film of water to reach eggs ORIGINS AND TRAITS OF VASCULAR PLANTS Main traits that characterize living vascular plants are life cycles with dominant sporophytes transport in vascular tissues called xylem and phloem and well developed roots and leaves including spore bearing leaves called sporophylls TRANSPORT IN XYLEM AND PHLOEM XYLEM conducts most of the water and minerals includes tracheids TRACHIEDS tube shaped cells that carry water and minerals up from the LIGNIFIED cell walls are strengthened by the polymer lignin PHLOEM has cells arranged into tubes that distribute sugars amino acids or Lignified vascular tissue enabled vascular plants to grow tall Tall plants outcompete short plants because access to sunlight is needed for Spores of tall plants can disperse further than those of short plants ROOTS organs that absorb water and nutrients from the soil They also roots other organic compounds photosynthesis EVOLUTION OF ROOTS anchor vascular plants EVOLUTION OF LEAVES LEAVES increase the surface area of the plant body and serve as the primary photosynthetic organ of vascular plants All of the lycophytes have and only the lycophytes have microphylls and megaphylls of vascular tissue MICROPHYLLS small often spine shaped leaves supported by a single strand MEGAPHYLLS leaves with a highly branched vascular system Typically larger and therefore support greater photosynthetic productivity SPOROPHYLLS AND SPORE VARIATIONS SPOROPHYLLS modified leaves that bear sporangia Fern sporophylls produce clusters of sporangia called SORI usually on the underside of the sporophylls Groups of sporophylls form cone like structures called STROBILI Most seedless vascular plant species are homosporous HOMOSPOROUS have one type of sporangium that produces one type of spore which typically develops into a bisexual gametophyte as in most ferns HETEROSPOROUS has two types of sporangia and produces two kinds of spores megaspores and microspores MEGASPORES develop into female gametophytes MICROSPORES develop into male gamteophytes CLASSIFICATION OF SEEDLESS
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