Plants II Chapter 30 - WCJCfacultyweb.wcjc.edu/users/kevind/documents/BIOL_1407... · 2020. 12....
Transcript of Plants II Chapter 30 - WCJCfacultyweb.wcjc.edu/users/kevind/documents/BIOL_1407... · 2020. 12....
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Chapter 30
Plant Diversity II – The Seed Plants
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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
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• 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
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• 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!!!!
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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
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Two groups of seed plants
Gymnosperms – “naked seed”Angiosperms – “enclosed seed”
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Gymnosperms
• Phylum Cycadophyta – the cycads– 130 spp.– Large cones (modified leaves that bear the sporangia)– “palm-like” leaves
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Gymnosperms
• Phylum Ginkgophyta– Only 1 extant species, Ginkgo biloba (the maidenhair tree)– Fan-like leaves– Popular ornamental in cities – tolerates air pollution well
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Gymnosperms
• Phylum Gnetophyta– 75 spp.– Only three genera– In North America – Ephedra, mormon tea produces ephedrine
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Gymnosperms
• Phylum Coniferophyta– The conifers – all produce cones (modified leaves that bear
sporangia)– Most diverse phylum – 600 spp.
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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
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Life cycle of typical conifer, Pinus
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Angiosperms• A better lifestyle
– Modified leaves to produce flowers (still contain sporagnia!!)
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• 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!!!
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Life cycle of typical flowering plantAngiosperms
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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????
Angiosperms
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Many plants and their animal pollinators have evolved together and are dependant
on one another (coevolution)
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Classification of Angiosperms
• Phylum Anthophyta– >250,000 spp.
• Two classes– Class Monocotyledones – MONOCOTS– Class Eudicotyledones – EUDICOTS
• Most successful group of plants– WHY????
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Benefits of flowering plants
• Food• Medical uses• Lumber/timber• Clothing• Recreation