Chapter 30. Plant Diversity II The Seed Plants

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Marilyn James
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1 Chapter 30 Plant Diversity II The Seed Plants

2 The rise of the seed plants Recall that our discussions on terrestrial plants up until this point have focused on a transition from the aquatic green algae to the non-vascular bryophytes to the seedless vascular plants We have seen the evolutionary trend of the removal of water from the plants life cycle (though not necessarily the removal of the needs of water to sustain life in plants) Recall that the bryophytes were dominated by the gametophyte portion of the life cycle and the seedless plants were dominated by the sporophyte HOWEVER both groups were HOMOSPOROUS

3 A shift from homospory to heterospory led to the development of the seed, as two different spore types produce two different gametophytes Microspores microgametophytes Megaspores megagametophytes Though the microgametophytes are smaller than the megagametophytes THEY are BOTH smaller than the gametophytes of the bryophytes and seedless vascular plants This miniaturization allows for important evolutionary innovations in the seed plants: The gametophytes can be protected by the sporophyte s tissues from environmental stress We can remove water from the life cycle

Within the sporophyte Ovule Integument surrounds and protects ;opening (micropyle) Megasporangium meiosis megaspores megagametophyte Microsporangium

5 Within the sporophyte Ovule Integument surrounds and protects ;opening (micropyle) Megasporangium meiosis megaspores megagametophyte Microsporangium meiosis microspores microganmetophyte (pollen grain) Fertilization sperm (usu. non-flagellated) + egg = zygote (2n) embryo Integument seed coat Ovule seed!!!!

6 There is an evolutionary advantage to reproduction with seeds: Seed is protected by seed coat Embryo inside of seed is supplied nutrients From female gametophyte tissue or endosperm (flowering plants) Seeds are able to cope with harsh environmental conditions can withstand a period of hot, dry, cold Seeds may be dispersed by several agents away from parent plant

7 Two groups of seed plants Gymnosperms naked seed Angiosperms enclosed seed

8 Gymnosperms Phylum Cycadophyta the cycads 130 spp. Large cones (modified leaves that bear the sporangia) palm-like leaves

9 Gymnosperms Phylum Ginkgophyta Only 1 extant species, Ginkgo biloba (the maidenhair tree) Fan-like leaves Popular ornamental in cities tolerates air pollution well

10 Gymnosperms Phylum Gnetophyta 75 spp. Only three genera In North America Ephedra, mormon tea produces ephedrine

11 Gymnosperms Phylum Coniferophyta The conifers all produce cones (modified leaves that bear sporangia) Most diverse phylum 600 spp.

in cooler climates Evergreen Some of the largest (>

12 Gymnosperms Phylum Coniferophyta Most conifers have modified leaves needles Water conservation measure Live in cooler climates Evergreen Some of the largest (> 110m) and oldest (4,600 years old) living things today are conifers

13 Life cycle of typical conifer, Pinus

15 Angiosperms A better lifestyle Modified leaves to produce flowers (still contain sporagnia!!)

16 Ovule seed Ovary fruit Fruits aids in the dispersal of the seeds (which they contain) Dispersal mechanisms Wind Animals seed coat protects seed from digestive tract Some seeds need to have the seed coat scarified (weakened) to allow for germination Some seeds are only allowed to germinate after they have passed through the digestive tract of an animal!!!

18 Angiosperms Life cycle of typical flowering plant

20 Angiosperms Life cycle of typical flowering plant Important key points Double fertilization Sperm + egg = zygote (2n) Sperm + polar nuclei = endosperm (3n) Pollination transfer of pollen grains to stigma of pistil Wind Animals Reward for animals efforts Pollen, nectar, floral parts are food sources Is there another way to reward an animal????

21 Many plants and their animal pollinators have evolved together and are dependant on one another (coevolution)

22 Classification of Angiosperms Phylum Anthophyta >250,000 spp. Two classes Class Monocotyledones MONOCOTS Class Eudicotyledones EUDICOTS Most successful group of plants WHY????

24 Benefits of flowering plants Food Medical uses Lumber/timber Clothing Recreation

Biology Slide 1 of 28

Biology Slide 1 of 28 Biology 1 of 28 2 of 28 22-4 Seed Plants Seed plants are the most dominant group of photosynthetic organisms on land. 3 of 28 22-4 Seed Plants Seed plants are divided into two groups: Gymnosperms bear