Chap 30 plant diversity 2-st-2011

Chap 30 plant diversity 2-st-2011 - Plant Diversity II The...

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Plant Diversity II: Plant Diversity II: The Evolution of Seed Plants The Evolution of Seed Plants
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Overview of seed plant evolution There were three (3) major reproductive adaptations in the evolution of seed plants. 1) Reduction of gametophyte (Gametophytes of seed plants are microscopic, so they can exist within the sporophyte ). 2) Seeds became an important means of dispersal. -Protect the seed, have specialized structures for dispersal 1) Pollen (Sperm cells) eliminated the liquid-water requirement for fertilization. -Can be transported by wind, animals
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1) Reduction of the gametophyte continued with the evolution of seed plants . In seed plants, the very small female (1N) gametophyte develops from spores retained in the sporangia of the (2N) sporophyte. [diploid- if one allele is defective, the other can take over] Delicate female gametophytes are protected from environmental stress. Embryos that are produced are also protected from stress. Why reduced and not eliminated? [ ploid] If there is a deleterious mutation, gametophyte will not survive genes will not be passed on Defective alleles are taken out of the population
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Three variations on gametophyte/sporophyte relationships
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Seeds became an important means of dispersal . Seeds are resistant to environmental stress, and are multi- cellular complex structures that consist of a sporophyte embryo, a food supply [endosperm, well developed in angiosperm], and a protective coat. The embryo develops from the fertilized egg retained within the sporangium. The sperm is carried (produced by) a pollen grain released from a sporangium. Some seeds need time for the seed coat to degenerate,
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Chap 30 plant diversity 2-st-2011 - Plant Diversity II The...

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