Introduction: Pioneers In a New World• Transition from water -> land began in the precambrian period with cyanobacteria (green algae)• Developed into world’s 1st plants• Adaptations necessary for survival on land - Obtaining and preserving water - Reproduction
23.1: Trends In Plant Evolution • Vascular plants: most diverse plants w/ internal tissue systems that conduct water and solutes through roots, stems and leaves • Seedless vascular plants: whisk ferns, lycophytes, horsetails, ferns • Gymnosperms: seed-bearing vascular plants – Cycads, ginkgos, gnetophytes, conifers • Angiosperms: vascular plants w/ flowers and seeds – Magnoliids, eudicots, monocots • Bryophytes: nonvascular plants – Liverworts, hornworts, mosses • Root systems: underground absorptive structures of a cumulatively large surface area – Rapidly take up soil water and mineral ions – Anchor for plants • Shoot systems: stems and leaves absorb energy from sun, CO2 from the air – Developed taller/branched stems after developing the capacity to synthesize/deposit lignin in cell walls • Xylem: vascular tissue that distributes water and dissolved ions in plants • Phloem: vascular tissue that distributes dissolved sugars and other photosynthetic products
23.1: Trends In Plant Evolution • Cuticle: protective waxy coat that helps conserve water on hot, dry days • Stomata (stoma): tiny openings across surfaces of leaves and some stems to control CO2 absorption and restrict evaporative water loss • Gametophytes: gamete-producing bodies that dominate the haploid phase of algal life cycles – mostly aquatic plants • Sporophyte: multicelled diploid plant body • After a diploid zygote undergoes mitosis->Forms spores: haploid resting cells – fertilization could be timed with suitable environmental conditions – Diploid dominance is an adaptation to land • Heterospory: plants that produce 2 types of spores (both seedless an seed- bearing) • Homospory: plants that produce one type of spore • Pollen grains: cellular structures that become mature, sperm-bearing male gametophytes – Microspores that reach eggs via air currents, insects, and birds – Contributed to radiation of seed-bearing plants to high/dry habitats • Seed: an embryo sporophyte, nutritious tissues, and outer coat; Developed from female gametophytes
23.2: The Bryophytes • Species of mosses, liverworts, hornworts – Adapted to moist habitats – Mosses, however, can be found in deserts as well • Sensitive to air pollution • Most common • Nonvascular: leaf/stem/root parts lack a xylem or phloem – Instead, have rhizoids: elongated cells/threadlike absorptive structures that attach the gametophytes to the soil, and absorb water and minerals • Show three features that were adaptive during the transition to land – 1. Cuticle: stomata to prevent water loss – 2. Cellular jacket around parts that produce sperm/eggs: holds in moisture – 3. Embryo sporophyte: sporophytes that begin life inside a female gametophyte • Sporophytes remain attached to the gamete-producing body for nutrition (do not disperse) • Mosses (most common) – Gametophytes grow in clusters to form cushiony mounds, or grow in branched patterns on tree trunks (humid conditions) – Eggs and sperm develop in gametangia at shoot tips of familiar moss plants – After fertilization, the zygote develops into a mature sporophyte • Develop a sporangium: stalk and jacketed structure where spores develop • o Examples • Peat mosses: used to soak up water (5x more than cotton), used as antiseptic, and also burned for electricity • peat bogs: moist mats of the remains of peat mosses
23.3: Existing Seedless Vascular Plants• Whisk ferns, lycophytes, horsetails, and ferns• Different from bryophytes b/c sporophytes that develop independently of gametophytes – sporophytes that have well-developed vascular tissues – larger, longer-lived sporophyte phase of its life cycle• Sporophytes can live on land, while gametophytes cannot• Lycophytes: small club mosses on the forest floor – “ground pines” – sporophytes with true roots, stems, small leaves with vascular tissue – strobili (strobilius) bear spores that germinate, forming small, free-living gametophytes • heterosporous• Whisk ferns: not true ferns; resemble whisk brooms – have rhizomes: short, branched, mainly horizontal absorptive stems that grow underground – no leaves, made of scale-like branches – popular ornamental plants common to tropical/subtropical areas• Horsetails – sporophytes have rhizosomes – scalelike leaves whorl around a hollow, photosynthetic stem – spores produced inside cone-shaped clusters of leaves at shoot tip – found in streambank muds and other disrupted habitats• Ferns – have rhizosomes and fronds: aerial leaves that coil into what resembles a fiddlehead – sporangia: clusters of spores on the lower surface of the fronds
23.4: Ancient Carbon Treasures• Lycophyte trees: giant club mosses that developed during the Carboniferous era – strobili that produced 8 billion microspores or hundreds of megaspores – 40m tall• 20m tall horsetails• Many swamp forests had sediments that compressed undecayed remains of plants into peat mosses – Pressure transformed the peat into coal: a renewable fossil fuel
23.5: The Rise Of Seed-Bearing Plants• Most successful vascular plants because independent of water for fertilization – Seed ferns, gymnosperms, angiosperms• Different than seedless vascular plants because: – Microspores: develop into pollen grains to carry sperm to female structures (pollination) – Megaspores: develop within ovules: female reproductive structures that, when mature, produce seed• § female gametophyte, nutrient rich tissue, jacket of cell layers (to develop a seed coat) – Traits to conserve water: Thicker cuticles, stomata underneath leaves• Pre-Carboniferous: dominated by seed ferns (simlar to progymnosperms): earliest seed-producing plants
23.6: Gymnosperms-Plants With “Naked” Seeds• Gymnosperm sporophyte stages are conspicuous trees and shrubs; the seeds are rather unprotected ("naked seeds") perched at the surface of reproductive parts.• Conifers (Coniferophyta) – The conifers (cone-bearers) are woody trees with needlelike or scalelike leaves. – Most are evergreens, some are deciduous. – Produce true cones: repro. structures in clusters of papery/wood-like scales that bear exposed to ovules on upper surface• Lesser Known Gymnosperms – Cycads (Cycadophyta) • These palmlike trees flourished during the Mesozoic era, but only about 100 species still exist--confined to the tropics and subtropics. • They bear massive cone-shaped strobili that produce either pollen (transferred by air currents or insects) or ovules. – Ginkgos (Ginkgophyta) • From the diversity of this group during the Mesozoic, only one species has survived. • They are remarkably hardy, showing resistance to insects, disease, and air pollutants. – Gnetophytes (Gnetophyta) are the most unusual gymnosperms; they live in tropical and desert areas.
23.7: A Closer Look At The Conifers• Pine Life Cycle – The pine tree produces two kinds of cones: • Male cones produce sporangia which yield microspores that develop into pollen grains (male gametophyte). • Female cones produce ovules that yield megaspores (female gametophyte). – Pollination is the arrival of a pollen grain on the female reproductive parts, after which a pollen tube grows toward the egg. – Fertilization, which is delayed for up to a year, results in a zygote that develops into an embryo within the conifer seed.• Deforestation and the Conifers – Although conifers still dominate in certain climates, their slow reproductive pace puts them at a disadvantage compared to angiosperms. – However, deforestation by clear-cutting for their commercial value has put them at even greater risk.
23.8: Angiosperms - Flowering, Seed-Bearing Plants• Characteristics of Flowering Plants – Only angiosperms produce specialized reproductive structures called flowers. • Of all the divisions of plants, angiosperms ("vessel seed") are the most successful and most diverse. • Most flowering plants coevolved with pollinators--insects, bats, birds, etc. – There are three major groups of flowering plants: • Magnoliids include magnolias, avocados, nutmeg, and black pepper plants. • Eudicots include familiar shrubs, trees (except conifers), and herbaceous plants. • Monocots include grasses, lilies, and the major food-crop grains.• Representative Life Cycle--A Monocot – The diploid sporophyte has extensive root and shoot systems; it also retains and nourishes the gametophyte. – Embryos are nourished by the endosperm within the seeds, which are packaged inside fruits.
23.9: Seed Plants And People• Artificial selection of plants led to the development of domesticated grains including wheat and barley (11,000 yrs ago)• Different trees have been used for their wood pliability (paper, furniture, rope)
Works CitedStarr, Cecie and Ralph Taggart. Biology: The Unity and Diversity of Life. 10th Ed. Belmont: Brooks/Cole, 2004. Print.