Angiosperms and course summary Lecture #18 Seed evolution and changing life cycles Homospory, heterospory and the seed habit Homospory Land plant life cycles Produce 1 size of spore Exosporic gametophyte development Free living gametophytes with multicelluar sex organs-antheridia and archegonia Free sporing plants (=shed their spores from the sporangia) Need water for spore germination, gametophyte development and fertilization to take place Heterospory Produce 2 sizes of spores (megaspores and microspores) Endosporic gametophyte development (inside of spore wall) Free sporing plants Only need water for fertilization as gametophytes develop inside the spore wall Seed habit - gymnosperms • Plants produce 2 sizes of spores • Endosporic gametophytes • Megasporangium never sheds its megaspore – i.e., it is not free sporing • Has eliminated the need for water in the completion of the life cycle • New to seed plants-the integument, pollen tubes that deliver the pollen to the archegonia or close to it. Cycads-swimming sperm Conifers-non-flagellate sperm Nucellar apex Cycads & Ginkgo have multiflagellate sperm Pinus microgametophyte development Seed habit- angiospermy • Plants produce 2 sizes of spores • Endosporic gametophytes • Megasporangium never sheds its megaspore – i.e., it is not free sporing • Seeds – double integumented megasporangium enclosed in a carpel • The megagametophyte has no archegonia and only one egg • The microgametophyte is only 3 cells total (vs. 6 cells in pines and 5 cells in cycads, 32 cells in heterosporous plants like Selaginella) Characters of angiosperms • Carpel encloses the seeds • Double integument for seed • Flowers – determinate stem tip with leaves and modified leaves that bear the pollen and seeds • 7-celled, 8 nucleate megagametophyte (= embryo sac) 3 antipodals, 2 synergids, 1 egg, large central cell with 2 nuclei • 3-celled microgametophyte tube cell (pollen tube) and 2 sperm-each sperm used • Double fertilization egg + sperm = zygote polar nuclei + sperm= endosperm Angiosperm Ovule Central cell Nucellus 7 celled embryo sac = megagametophyte Angiosperm Ovule Double fertilization Central cell 2 sperm Nucellus Pollen tube 7 celled embryo sac = megagametophyte Primary endosperm nucleus 3n (degenerate) xx x (degenerate) x x Zygote 2n 2n 2n 3n Capsella mature embryo l.s. Pollination in Angiosperms . The transfer of pollen from the anther to the stigma . Pollination droplet Integument Megaspore Ovule enclosed in carpel Pollination in gymnosperms Nucellus The transfer of pollen from the pollen sac to the micropyle of the seed/ovule Parts of a typical gymnosperm seed micropyle outer layer of the integument= sarcotesta stony layer=sclerotesta inner layer=endotesta nucellar beak pollen chamber nucellus=megasporangium archegonial chamber archegonium with egg Cycad ovule megagametophyte Angiosperm Ovule Central cell Nucellus 7 celled embryo sac = megagametophyte Angiosperm life cycle Text book, Pages 472-473; Also, see self-test exercise on course web site Today’s Lab a series of demonstration slides on the angiosperm life cycle 18 stations (17 from Lilium life cycle –a monocot and 1 from Capsella life cycle that we saw last lab – a dicot) Use this as a review, and to see these stages on slides No drawings today Final Exam: March 19, 8:00 a.m. 1070 Cordley Hall • Exam will cover all material taught in the course • Exam will emphasize material not covered in exams 1 and 2 • Exam will be of the same structure as previous exams • Exam will cover Labs 13-17 in detail (seed plants) • Exam will cover lectures 13-18 in detail (seed plants)- i.e., Feb. 17- Mar 12 lectures on course website Please use the extra material available on the website links: Hydrasperman Reproduction Life Cycle of an Angiosperm (also, reviews of fern life cycle and Equisetum (homospory) are available there)
© Copyright 2024