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Life on Earth Kingdom Plantae Part IV The Seed Plants: Gymnosperms.

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Presentation on theme: "Life on Earth Kingdom Plantae Part IV The Seed Plants: Gymnosperms."— Presentation transcript:

1 Life on Earth Kingdom Plantae Part IV The Seed Plants: Gymnosperms

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3 Origin of the Seed Female Gametophyte Scenario Megasporangium produces only one functional megaspore Megaspores are not released from the plant Megaspore develops into the female gametophyte within the old megasporangium

4 Origin of the Seed (cont.) Archegonia are formed with egg cells and fertilized in situ Embryo (new sporophyte) develops surrounded by female gametophyte tissue and old megasporangium wall (nucellus)

5 Origin of the Seed (cont.) Megasporophyll surrounds the structure and acts as integument (seed coat) The mature ovule (seed) is released from the plant (old sporophyte)

6 Origin of Pollen Male Gametophyte Scenario Micorsporophylls produce microsporangia Microspores (N) are not released from the microsporangium but divide to form a 4- celled microgametophyte (pollen grain) Four cells are 2 prothallial cells, 1 generative cell and 1 tube cell

7 Pine Pollen

8 Origin of Pollen (cont.) Pollen grains (male gametophytes) are released from the “strobilus” or “cone” The pollen grains germinate forming a pollen tube The generative cell divides to form sperm nuclei which travel down the pollen tube to fertilize the egg

9 Why evolve seeds and pollen? Embryo is well protected in the seed coat Seeds can be “dormant” and wait for suitable growth conditions Transfer of pollen (male to female) does not require water like sperm

10 Why evolve seeds and pollen? (cont.) Embryo has a ready supply of nutrients for early development (female gametophyte tissue) A seed is an excellent dispersal unit (wind, animals)

11 Seed Plant Divisions Gymnosperms –plants with “naked” seeds not found in a fruit –includes 4 Divisions Angiosperms –seed plants with “hidden” seeds, i.e. formed inside a fruit –only one Division

12 Gymnosperms Coniferophyta Cycadophyta Ginkgophyta Gnetophyta

13 Division Coniferophyta Most species are monoecious, woody perennials producing cones Some are deciduous, most are evergreen with needle- like leaves Extended life cycle (3 years)

14 Primary vs. Secondary Growth Primary tissues are derived from meristems –Zones of cell division in root tips, shoot tips, axillary buds etc. –Primary growth generally creates elongation of stems, branches, and roots or creates reproductive organs

15 Primary vs. Secondary Growth (cont.) Secondary tissues are derived from cambia –Cambial activity generally causes increase in girth of the plant (root, stem) –Woody plants develop 2 cambia: vascular cambium (producing secondary xylem and phloem) cork cambium (producing “bark” layers)

16 Pine Anatomy (stem) PITH RESIN DUCT VASCULAR CAMBIUM SECONDARY XYLEM SECONDARY PHLOEM

17 Wood Sections RADIAL TANGENTIAL TRANSVERSE Wood Rays

18 Pine Needles

19 Pine Life Cycle Trees produce both male (staminate) and female (ovulate) cones Male cones are usually lower on the tree to assist with out-crossing Pollination takes place in the spring when female cones are small (about 1/2 inch)

20 Pine Life Cycle (cont.) Development of the mature ovule with archegonia takes more than a year Pollen tube digests its way slowly through the nucellus to the archegonium for fertilization Nearly another year is required before the embryo is mature and the female cone opens to release the seeds

21 Pine Life Cycle

22 Pinus (male and female cones )

23 Male Cone (longitudinal Section)

24 Conifer Diversity Highly diverse in both Northern and Southern Hemispheres –Includes pine, spruce, hemlock, fir, Douglas fir, yew, juniper, cypress, sequoia, larch, podocarps, araucarias and others

25 Taxodium (bald cypress)

26 Giant Sequoia Taxus (yew) with female cones

27 Sequoia and Sequoiadendron

28 Araucaria family –Wollemi “pine,” discovered living in Australia, 1994, known from Jurassic fossils

29 Aucariaceae ( Southern Hemisphere ) Norfolk Island Pine

30 Division Cycadophyta Perennial, dioecious plants with coarse palm-like leaves Female cones are often very large Only 10 genera known - many with highly restricted ranges, primarily tropical Produce flagellated sperm

31 Cycas revoluta and C. media With “female cone” and seeds

32 Dioon edule

33 Encephalartos

34 Division Ginkgophyta Ginkgo biloba only species Probably extinct in the wild (originally from China) Separate male and female trees (dioecious)

35 Division Ginkgophyta (cont.) Female ovules produce butyric acid (plant males!) Male trees produce small, fleshy pollen cones; motile sperm are produced Tolerates air pollution well

36 Ginkgo biloba

37 Ginkgo Leaves and Ripe Ovules

38 Division Gnetophyta Gnetum, Ephedra (Mormon Tea) and Welwitschia very different organisms Have vessels in the xylem Do not produce multicellular archegonia Have double fertilization Ephedra male cones

39 Gnetophyta (cont.) Gnetum is a genus of tropical vines with flowering plant-like leaves Ephedra is a desert shrub with several species in the SW United States (called Mormon Tea) Welwitschia mirabilis is a bizarre, tap- rooted, perennial plant of the desert areas of SW Africa

40 Ephedra nevadensis

41 Welwitschia mirabilis Habitat view in SW Africa

42 Welwitschia mirabilis in Namib Desert, Namibia

43 Welwitschia mirabilis -female (with ovulate cones)

44 Welwitschia mirabilis - male (with staminate cones)

45 Gnetum With Ovules

46 Importance of Gymnosperms Major source of lumber for construction Primary source of pulp for paper manufacture Many ornamentals Source of resins for turpentine, rosin (“naval stores”) Juniper (“berries”) used to flavor gin Source of amber and even lemon flavoring Anticancer drug taxol from Pacific yew bark/ English yew leaves

47 Importance of Gymnosperms TAXOL: 31 years from “bark” to “business” Originally took 4 trees to produce a single human dose! Now, using leaves of common English yew, a synthetic process makes the drug.


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