Botany BIO 201 Notes 4-18
Botany BIO 201 Notes 4-18 BIOL 201
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This 6 page Class Notes was uploaded by Sarah Martin on Friday April 22, 2016. The Class Notes belongs to BIOL 201 at Kansas State University taught by Dr. Ari Jumpponen in Spring 2016. Since its upload, it has received 10 views. For similar materials see Organismic Biology in Biology at Kansas State University.
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Date Created: 04/22/16
BIO 201 Notes 4/18 Gymnosperms cont... 4 extant phyla: 1)Cycadophyta: tropical cyads; palm-like leaves; flagellated sperm 2)Ginkgophyta: 1 species: Ginkgo biloba; flagellated sperm; heart-shaped leaves; deciduous (turns bright yellow before leaves drop); dioecious; pollen delivers sperm to ovule then eggs engulf the sperm cell; outside layer of seed stinks 3)Pinophyta: conifers; most successful because of sunken stomata to reduce water loss; drought resistant; thick cuticles; however, the more water they retain, the less CO2 they can take in because there is no room 4)gnetophyta: gnetophytes; 3 genera: a)Ephedra: weight loss supplement because it raises metabolism and heart rate however, bad side effect that caused heart attacks b)Gnetum: c)Welwitschia: basal meristem (pushes leaves out from the bottom); central concave woody stem; attempts double fertilization which could make closely related to angiosperms with a common ancestor; also things that could make them closely related to angiosperms: vessels (not tracheids) in xylem and aborted ovule in pollen cone suggesting monoecious (potentially bisporangiate) ancestor; most angiosperms are monoecious ?) Megasporocyte... resides in megasporangium so no A, no B, yes C, no D, it is the mother cell so not E Angiosperms: ?) Angiosperms: all of the above: have seeds, flowers, endosperm, and double fertilization; E all of the above Welwitschia: produces only 2 leaves every 100 yrs; most similar to angiosperms; absorbs moisture through fog because it is a desert plant; dioecious; Welwitschia may represent an intermediate species during the evolution of Double Fertilization; Where the endosperm (3n) is NOT used as “food” for the germinating seed; Is Welwitschia a gymnosperm or angiosperm? gymnosperm because it doesn't produce any flowers ?) Angiosperms replaced gymnosperms because... feasible A Small dinosaurs ate the gymnosperms, no B Angiosperms were insect pollinated, no C An asteroid wiped the gymnosperms out, YES D A or B, no E B or C Origins: late Cretaceous (125 mya); cool, dry uplands; emergence of angiosperms probably coincided with dino extinction; Angiosperm dominance: Dinos: large herbivores were replaced by smaller ones that ate different plants and angiosperms reproduce faster; Insect pollination: greater accuracy and energy conservation Cycadeoids: extinct seed plants; extinct at the end of the cretaceous (with dinos); bisporangiate (protected reproduction); almost flower-like Most gymnosperms had male and female sporangia in different cones; cycadeoids bisporangiate; Welwitschia had an abortive ovule and almost double fertilization (bisporangiate?); angiosperms have male and female parts in one flower + double fertilization Competing hypothesis of the origins: 2nd pushes the timeline back to 200 mya while the 1st claims that 120 mya was when they emerged; Darwin says that sudden and abundant emergence in the fossil record is a mystery Potential common ancestor: not flashy; bisporangiate; double fertilization; Ceratophyllum looks like early flowering plants: acquatic; monoecious; single- chambered carpel; bisporangiate strobilus of the cycadeoids from 4/22 Angiosperms cont. Angiosperms are flowering plants Seed: enclosed in carpel, carpel resembles a leaf that has folded over and fused at the margins, develops from ovule in the carpel Pistil composed of 1,2, or more carpels Ovary becomes the fruit: great advantage because of dispersal Phylum Magnoliophyta: 2 big classes: Magnoliopsida: dicots, 2 cotyledons, DNA suggests 2 or potentially more dicot groups Liliopsida: monocots, single cotyledon Flower is modified stem with modified leaves Most primitive flowers: long receptacle, many spirally arranged flower parts that are separate and not differentiated into sepals and petals, flattened and numerous stamens and carpels Heterosporous Sporophyte dominant Female gametophyte enclosed within sporophyte tissue and reduced to only a few cells Male gametophyte only has 3 nuclei: tube cell nuclei and 2 sperm with one each micro and mega gametophytes are greatly reduced compared to non-flowering vascular plants Structure and function of a flower: Stamen: microspore producing organ Anthers: fused, microspore-containing chambers Filament: supports anthers Pistil: megaspore-producing organ Stigma: area capturing the pollen Style: elevates stigma to enhance pollination Ovary: swollen base of the pistil, contains ovules Ovule: More later Petals (corolla): odor + color to attract the pollinators, shape to make sure that the pollen sticks Sepals (calyx): protect the inner flower parts prior to opening Receptacle: tip of the flower stalk upon which the other parts are attached Peduncle: the main axis of an inflorescence on which individual flowers arise - stem Stamens deliver pollen: stigma receives pollen and holds it until fertilization has taken place How the female gametophyte is developed: Diploid megasporocyte differentiates in ovule. Undergoes meiosis and produces four haploid megaspores. Three degenerate. Remaining cell enlarges and nucleus divides to produce 8 nuclei (without walls). Outer two layers of ovule differentiate into integuments that later become seed coat. Micropyle at one end of ovule 8 nuclei form two groups, 4 near each end of cell. One nucleus from each group migrates to cell middle and forms central cell. Cell walls form around remaining six nuclei. Egg and two synergids closest to micropyle Three antipodals at opposite end - No apparent function Female gametophyte (megagametophyte, embryo sac) = large sac containing 8 nuclei and 7 cells How the male gametophyte is developed: Formation of male gametophytes in anthers. Four patches, corresponding to pollen sacs, of microsporocyte cells differentiate in anther. Each microsporocyte undergoes meiosis to produce quartet of haploid microspores. Microspores undergo three important changes: Divide once by mitosis to form a small generative cell inside the larger tube cell Nucleus of tube cell = vegetative nucleus Members of each quartet of microspores separate. Wall becomes two-layered. Outer layer = exine Finely sculptured Contains chemicals that may react with chemicals in stigma Generative nucleus will later divide to produce two sperm. Pollination - Transfer of pollen grains from anther to stigma Self-pollination - Pollen grains germinate on stigma of same flower. Fertilization - Union of sperm and egg Pollination by insects, wind, water, animals or gravity. Mature male gametophyte = germinated pollen grain with its vegetative nucleus and two sperms within tube cell Fertilization and development of the seed: After pollination, male gametophyte may not develop unless pollen grain is: From a different plant of the same species. From a variety different from that of the receiving flower. Pollen tube grows between cells of stigma and style until it reaches ovule micropyle. Vegetative nucleus stays at tips of pollen tube, while generative cell lags behind and divides into two sperm. Pollen tube enters female gametophyte, destroying synergid in the process, and discharges sperms. C answer for pic. where fertilization (?) takes place Pollen isn't mature until it produces a pollen tube
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