Chapter 30 - Chapter 30 - Plant Diversity II: The Evolution...

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Chapter 30 - Plant Diversity II: The Evolution of Seed Plants Chapter 30 Plant Diversity II: The Evolution of Seed Plants Lecture Outline Overview: Feeding the World The seed arose about 360 million years ago. o Seed plants, including gymnosperms and angiosperms, have come to dominate modern landscapes and make up the great majority of plant biodiversity. Agriculture, the cultivation and harvest of plants (especially angiosperms), began 13,000 years ago. o Humans began the cultivation of plants independently in various regions, including the Near East, East Asia, Africa, and the Americas. o This was the single most important cultural change in the history of humanity, and it made possible the transition from hunter-gatherer societies to permanent settlements. Concept 30.1 The reduced gametophytes of seed plants are protected in ovules and pollen grains A number of terrestrial adaptations contributed to the success of seed plants. o These adaptations include the seed, the reduction of the gametophyte generation, heterospory, ovules, and pollen. Bryophyte life cycles are dominated by the gametophyte generation, while seedless vascular plants have sporophyte-dominated life cycles. The trend to gametophyte reduction continued in the lineage of vascular plants that led to seed plants. o Seedless vascular plants have tiny gametophytes that are visible to the naked eye. o The gametophytes of seed plants are microscopically small and develop from spores retained within the moist sporangia of the parental sporophyte. In seed plants, the delicate female gametophyte and the young sporophyte embryo are protected from many environmental stresses, including drought and UV radiation. o The gametophytes of seed plants obtain nutrients from their parents, while the free- living gametophytes of seedless vascular plants must fend for themselves. Heterospory is the rule among seed plants. Nearly all seedless plants are homosporous, producing a single kind of spore that forms a hermaphroditic gametophyte. o Seed plants likely had homosporous ancestors. All seed plants are heterosporous, producing two different types of sporangia that produce two types of spores.
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o Megasporangia produce megaspores, which give rise to female (egg-containing) gametophytes. o Microsporangia produce microspores, which give rise to male (sperm-containing) gametophytes. Seed plants produce ovules. In contrast to the few species of heterosporous seedless vascular plants, seed plants are unique in retaining their megaspores within the parent sporophyte. Layers of sporophyte tissue, integuments, envelop and protect the megasporangium. o Gymnosperm megaspores are surrounded by one integument. o
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This note was uploaded on 08/23/2011 for the course BIO 101 taught by Professor Taylor during the Spring '11 term at University of West Georgia.

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Chapter 30 - Chapter 30 - Plant Diversity II: The Evolution...

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