Chapter 30 Lecture - Seed Plant Evolution PDF

2/11/22 2 The Evolution of Seed Plants Seed plants first appeared 305–465 MYA Evolved from spore-bearing plants known as progymnosperms SEED PLANTS Success attributed to evolution of seed Protects and provides food for embryo Allows the “clock to be stopped” to survive harsh periods before germinati...

2/11/22 2 The Evolution of Seed Plants Seed plants first appeared 305–465 MYA Evolved from spore-bearing plants known as progymnosperms SEED PLANTS Success attributed to evolution of seed Protects and provides food for embryo Allows the “clock to be stopped” to survive harsh periods before germinating Later development of fruits enhanced dispersal Chapter 30 1 1 2 3 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Seed plants produce 2 kinds of S to red fo o d gametophytes Male gametophytes In teg u m en t (seed co at) E m b ryo Pollen grains Dispersed by wind or a pollinator No need for water Seed Embryo protected by integument right: © Biology Media/Photo Researchers, Inc. 300 µm Female gametophytes Develop within an ovule Enclosed within diploid sporophyte tissue in angiosperms An extra layer or two of sporophyte tissue Hardens into seed coat Megasporangium divides meiotically inside ovule to produce haploid megaspore Megaspore produces egg that combines with sperm to form zygote Also contain food supply for embryo 3 4 5 6 Coniferophyta Cycadophyta Gnetophyta Ginkophyta Anthophyta Plants with “naked seeds” There are four living groups Coniferophytes Cycadophytes Gnetophytes Ginkgophytes Angiosperms Gymnosperms Gymnosperms Five Phyla of Extant Seed Plants Ferns and Allies Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. All lack flowers and fruits of angiosperms All have ovule exposed on a scale 6 5 6 1 2/11/22 7 8 Pines More than 100 species, all in the Northern hemisphere Produce tough needlelike leaves in clusters Leaves have thick cuticle and recessed stomata to retard water loss Leaves have canals with resin to deter insect and fungal attacks Conifers (phylum Coniferophyta) Most familiar gymnosperm phylum Pines, spruces, firs, cedars, and others Coastal redwood – Tallest living vascular plant Bristlecone pine – Oldest living tree Found in colder and sometimes drier regions of the world Conifers are sources of important products Timber, paper, resin, and taxol (anti-cancer) 7 8 9 P o llen M icro sp o res Pine reproduction Male gametophytes (pollen grains) A ir b lad d er P o llin atio n M icro sp o re m o th er cell Develop from microspores in male cones by meiosis SIS MEIO 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S cale Female pine cones form on the upper M eg asp o re P o llen tu b e S p erm P o llen tu b e IS OS MIT (15 m o n th s FE RT ILIZ AT ION M eg asp o re m o th er cell branches of the same tree n 2n P o llen - Female cones are larger, and have woody scales Two ovules develop on each scale Each contains a megasporangium b earin g co n e O vu late (seed -b earin g ) co n e after p o llin atio n ) Z yg o te S p o ro p h yte Each will become a female gametophyte MITOSIS S eed lin g MITOSIS S ectio n o f seed (seco n d year), P in e sh o w in g em b ryo em b ed d ed in m eg ag am eto p h yte seed 9 10 11 12 Female cones usually take 2 or more seasons to mature During the first spring, pollen grains drift down between open scales Pollen grains drawn down into micropyle Scales close Pollen tube is digesting its way through Mature male gametophyte has 2 sperm 15 months after pollination, pollen tube reaches archegonium and discharges contents 11 Slow-growing gymnosperms of tropical and subtropical regions Sporophytes resemble palm trees Female cones can weigh 45 kg Have largest sperm cells of all organisms! A year later, female gametophyte matures Cycads (phylum Cycadophyta) One sperm unites with egg = zygote Other sperm degenerates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. © Luca Invernizzi Tetto/agefotostock 12 2 2/11/22 13 14 Gnetophytes (phylum Gnetophyta) Ginkgophytes (phylum Ginkgophyta) Only gymnosperms with Only one living species Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. vessels in their xylem Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. remains Contain three (unusual) Ginkgo biloba genera Flagellated sperm Welwitschia Ephedra Gnetum Dioecious Male and female reproductive structures form on different trees b. © Juan Carlos Muñoz/agefotostock 13 c. © Robert Gustafson/Visuals Unlimited 14 15 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Angiosperms Ferns and Allies Flowering plants Ovules are enclosed in diploid tissue at the time of pollination Carpel, a modified leaf that covers seeds, develops into fruit Angiosperm origins are a mystery Gymnosperms Origins as early as Angiosperms 145–208 MYA Oldest known angiosperm in the fossil record is Archaefructus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ovules (seeds) Carpel (fruit) Ovules Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fruits Paired stamens Cross section © David Dilcher and Ge Sun Modified leaf with ovules Folding of leaf protects ovules Fusion of leaf margins 123435$.67,)89$:$;33#*,33)