Seed Plants: Gymnosperms and Angiosperms

1. Chapter 27 : Plant Kingdom: Seed Plants

2. Seeds • Multicellular young plant with embryonic root, stem and its leaves • Develop from fertilized egg, female gametophyte and its tissues • Protected by seed coat • Embryonic sporophyte

3. Gymnosperms and Angiosperms bear seeds • Seed develops from ovule (megasporangium and its enclosed structures) • Layers of sporophyte tissue surrounding and enclosing megasporangium make the integuments • Seed coat develops from integuments after fertilization

4. Fig. 30-3-1 Integument Spore wall Immaturefemale cone Megasporangium(2n) Megaspore (n) (a) Unfertilized ovule

5. Gymnosperms and Angiosperms • Vascular tissue • Xylem and phloem • Alternation of generations • Dominant sporophyte, gametophyte reduced • No free-living gametophytes • Dependent on sporophyte • All heterosporous: microspores and megaspores

6. Gymnosperms • “naked seed” • Pine, spruce, fir, hemlock, Gingko • 4 phyla • Coniferophyta – conifers • Gingkophyta – gingko • Cycadophyta – cycads • Gnetophyta – gnetophytes (unusual)

7. Conifers • Pine, spruce, fir, hemlock • Most familiar • Woody • Produce annual secondary tissue (wood +bark) • Wood (secondary xylem) • Tracheids – long, tapering cells with pits; water and dissolved nutrient minerals move between cells

8. Fig. 30-5h Douglas fir

9. Fig. 30-5i European larch

10. Fig. 30-5j Bristlecone pine

11. Fig. 30-5k Sequoia

12. Fig. 30-5l Wollemi pine

13. Fig. 30-5m Common juniper

14. Resin – produced by conifers • Viscous, clear • Protection – insects, fungi • Collects in resin ducts (roots, stems, leaves) • Produced and secreted by cells lining resin ducts

15. Needles - conifers • Long, narrow, tough, leathery • Pines – clusters; 2-5 needles • American arborvitae – scalelike and cover stem • Most evergreen • Few deciduous – Dawn redwood, larch, bald cypress

16. Conifers continued • Most monoecious – separate male and female reproductive parts – different locations, same plant • Parts borne in strobili called cones

17. Ecological importance • Food and shelter – animals • Roots – hold soil, prevent erosion • Wood – building, paper, medicine, turpentine, resins • Landscape design – trees, wreaths

18. Pines • Pine tree – mature sporophyte • Heterosporous – microspores and megaspores produced in separate cones • Male cones - < 1 cm; lower branches; spring • Female cones – woody; familiar; year round; upper branches; bear seeds; vary in size

19. Male cone (pollen cone) • Composed of sporophylls = leaflike structures – bear sporangia on underside • Base of each sporophyll = 2 microsporangia (contain numerous sporocytes) • Each microsporocyte  meiosis  4 haploid microspores  reduced male gametophyte (pollen grain) • Each pollen grain: 4 cells + 2 large air sacs (buoyancy , wind) • 1- generative cell • 1- tube cell • 2 - degenerate

20. Male Pine Pollen Cone

21. Pine Pollen Cone

22. Female cone (seed cone) • Each cone scale – 2 megaporangia on upper surface • Megasporangium  meiosismegasporocyte 4 haploid megaspores • 1 megaspores  mitosis  female gametophyte  egg • Other 3 cells degenerate

23. Female Pine Cones

24. Pine Ovulate Cone

25. Pine Ovule

26. Pollination • Pollen to female cones • Spring - week to 10 days • Then pollen cones wither and drop • Pollen grains adhere to sticky surface (produced by ovule when ready)

27. Conifer adaptation • Eliminate need for external water for sperm transport • Instead  air and pollen tube

28. Fig. 30-6-4 Key Haploid (n) Ovule Diploid (2n) Ovulatecone Megasporocyte (2n) Integument Pollencone Microsporocytes(2n) Megasporangium(2n) Maturesporophyte(2n) Pollengrain Pollengrains (n) MEIOSIS MEIOSIS Microsporangia Microsporangium (2n) Survivingmegaspore (n) Seedling Archegonium Femalegametophyte Seeds Foodreserves(n) Spermnucleus (n) Seed coat(2n) Pollentube Embryo(2n) FERTILIZATION Egg nucleus (n)

30. Cycads • Phylum Cycadophyta • Seed cones ; compound leaves • Important Triassic period • Tropical • Resemble palms • Lifecycle like pines BUT • Dioecious (seed cones – female plants; pollen cones – male plants) • Motile sperm cells

31. Fig. 30-5a Cycas revoluta

32. Gingkoes • Phylum Gingkophyta • Single living species – Gingko biloba • China and Japan • Resistant air pollution  cities • Deciduous • Dioecious, flagellated sperm, no cones • Female trees – fleshy seed covering  rancid butter • Medicinal – neurological function; memory

33. Fig. 30-5b Ginkgo bilobapollen-producing tree

34. Fig. 30-5c Ginkgo bilobaleaves and fleshy seeds

35. Gnetophytes • Phylum Gnetophyta • More advanced • Vessel elements in xylem • Cone clusters resemble flower clusters • Lifecycle resembles angiosperms • 3 genuses – Genus Ephedra - ephedrine

36. Fig. 30-5d Gnetum

37. Fig. 30-5e Ephedra

38. Fig. 30-5f Welwitschia

39. Fig. 30-5g Ovulate cones Welwitschia

40. Angiosperms • Phylum Anthophyta • “seed enclosed in a case or vessel” (fruit) – ovules are protected • Flowering (sexual reproduction) – double fertilization • Vascular - vessel elements; sieve tube members • Most successful – almost every habitat • Corn, oak, lilies, cacti, apples, grass, palms

41. Angiosperm importance • Food crops – our survival • Wood – lumber • Fibers – cotton, linen • Medicine – codeine • Products – rubber, tobacco, coffee, chocolate, aromatic oils

42. 2 classes of Angiosperms : Monocots and Dicots • Monocotyledones – palms, grasses, orchid, iris, onion, lilies • Mostly herbaceous • Long, narrow leaves – parallel veins • Flower parts – 3’s • Single cotyledon • Endosperm present

43. Fig. 30-13e Orchid

44. Fig. 30-13e1 Pygmy date palm (Phoenix roebelenii)

45. Fig. 30-13f

46. Fig. 30-13g Barley Anther Stigma Ovary Filament

47. Dicotyledones – oaks, roses, mustards, cacti, blueberries, sunflowers • More diverse • Herbaceous or woody • Leaves vary in shape (broader) – netted veins • Flower parts - 4’s or 5’s • 2 cotyledons • Endosperm absent

49. Fig. 30-13h California poppy

50. Fig. 30-13i Pyrenean oak