Chapter 30 Evolution of seed Plants Seed embryo and its food supply surrounded by a protective coat o Key adaptation that helped seed plants become dominant producers on land Seeds and Pollen Grains are Key Adaptations for life on land Common to all seed plants reduced gametophytes heterosporous 3 ovules and pollen grains o Provided new ways for seed plants to cope with drought and exposure to UV light o Advantages of reduced gametophytes Gametophytes can develop from spores in sporangia protecting them from environment drying out and UV radiation and allowing them to get nutrients from sporophyte o Heterospory the rule among seed plants Heterosporous make 2 types of spores Megasporangium has one megaspore that develops into an egg Most seedless plants are homosporous o Ovules and production of eggs Microsporangium microspores that develop into many sperm Seed plants retain the megasporangium within the sporophyte Integument layer of sporophyte tissue that envelopes and protects the megasporangium Gymnosperms have 1 integument Angiosperms have 2 integuments Ovule made up of megasporangium megaspore and integuments Female gametophyte inside makes eggs o Pollen and production of sperm Pollen grain develops from microspore male gametophyte in a pollen wall Pollen wall made of polymer sporopollenin Pollination transfer of pollen to the part of the seed plant with the ovule Pollen germinates into a pollen tube Pollen eliminates the dependence on water Can be carried long distances by wind animals Sperm carried directly to eggs by pollen tubes Evolutionary advantage of seeds o After fertilization the zygote develops into a sporophyte embryo o The who ovule becomes a seed Embryo with food supply and protective coat o Spores could survive adverse conditions Small size could easily disperse o Seeds can be dormant for years Have a supply of stored food Can be carried long distances Gymnosperms Bear naked seeds Naked seeds on sporophylls modified leaves that usually from strobili cones Progymnosperms transition species of seedless vascular plants o Archaeopteris heterosporous tree with woody stem but didn t bear seeds Dryer climate of the Permian period favored gymnosperms o Amphibians replaced by reptiles o Lycopetes horsetails and ferns replaced by gymnosperms o Gymnosperms well adapted to drier conditions because of pollen and seeds but also that they had thick cuticles and needle shaped leaves Phylum cycadophyta large cones and palm like leaves Phylum ginkgophyta ginkgo Bilbao the only surviving species Phylum gnetophyta grouped based on molecular data o 3 genera Welwitschia have strap like leaves Ephedra desert shrubs Gnetum tropical trees shrubs and vines Leaves look similar to flowering plants Fruit look like angiosperm fruits Phylum coniferophyta o Spruce fir pine and redwood o Cover vast regions in northern latitudes o Largest of the gymnosperm phyla o Many are large trees o Most evergreens o Lifestyle of a pine Sporangia on scale like structures densely packed in cones Heterosporous Staminate cones microsporocytes make microspores through meiosis that develop into pollen Ovulate cones megasporocytes make megaspores that develop into eggs Mature gametophytes kept in sporangia 3 years from start to seed Scales of cone separate and seeds are dispersed by wind Reproductive Adaptations of Angiosperms include Flowers and Fruits Characteristics of Angiosperms o Flower specialized shoot used for reproduction Pollinated by wind and animals Up to 4 rings of modified leaves Sepals base of flower green and enclose flower before it opens Petals brightly colored and attract pollinators wind pollinated lack bright colors o Sepals and petals are sterile floral organs Stamen produce microspores that develop into male gametophyte containing pollen grain o Filament stalk o Anther terminal sac where pollen is made Carpel make megaspores and female gametophytes o Stigma sticky part of carpel that receives pollen o Style connects carpel to ovary Ovary 1 or more ovules which develop into seeds when fertilized o Fruit mature ovary and sometimes other parts Fleshy wall pericarp softens during ripening Dry some split at maturity Ways to disperse seeds Wind water animals ingested carried Angiosperm life cycle o Flower makes male gametophytes sperm from microspores and female gametophytes eggs from megaspores Each male gametophyte has 2 haploid cells Generative cell divides to make 2 sperm Tube cell makes pollen tube Embryo sac female gametophyte only made up of a few cells o Pollination when the pollen gets to the sticky stigma Cross pollination pollen transferred between different individuals of the same species Enhances genetic variability Pollen grain germinates Tube cell makes a pollen tube down the carpel through the micropyle and deposits sperm o Micropyle pore in integuments of the ovule Double fertilization one sperm fertilizes the egg to make a diploid zygote while the other fertilizes 2 polar bodies to make a triploid endosperm Ovule develops into a sporophyte embryo with a root and 1 or 2 cotyledons seed leaves o Triploid cells develop into endosperm tissue rich and other food for the embryo Double fertilization prevents wasted energy on infertile ovules Gnetophytes sometimes do double fertilization but 2 embryos are formed Angiosperm evolution o Fossil angiosperms petals sepals Angiosperm phylogeny Archaefructus sinensis have anthers and seeds in closed carpels but no Can be used to infer traits of common ancestor Probably woody o Gymnosperms are a monophyletic group o Angiosperm phylogeny depends on working out when clades diverged from each other o Developmental patterns in angiosperms 1 integument in gymnosperms 2 in angiosperms Developmentally similar to gymnosperms at the genetic level Angiosperm diversity o Originally divided into monocots and dicots Dicots now divided into Eudicot true dicots Basal angiosperms flowering plants of oldest lineages Magnoliids evolved later Monocots 1 cotyledon Parallel Vascular tissue scattered Root system Pollen grain with 1 opening Petals in Multiples of 3 Embryos Leaf venation Stems Roots Pollen Eudicot 2 cotyledons Netted Vascular tissue arranged in ring Tap root usually present Pollen grain q 3openings Evolutionary links between angiosperms and animals o Interactions between plants and animals have resulted in reciprocal evolution Flowers Petals in multiples of 4 or 5s o Bilateral symmetry flower petals symmetrical in 1 direction Makes it more likely
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