seed plants final

seed plants final - Biology 5B Seed Plants Overview:...

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Unformatted text preview: Biology 5B Seed Plants Overview: Transforming the World Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems A seed consists of an embryo and nutrients surrounded by a protective coat CONCEPT: Seeds and pollen grains are key adaptations for life on land In addition to seeds, the following are common to all seed plants Reduced gametophytes Heterospory Ovules Pollen Advantages of Reduced Gametophytes The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte CONCEPT: Seeds and pollen grains are key adaptations for life on land In addition to seeds, the following are common to all seed plants Reduced gametophytes Heterospory Ovules Pollen Advantages of Reduced Gametophytes The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Reduced, independent (photosynthetic and free-living) Gametophyte Sporophyte (2 n ) Sporophyte (2 n ) Gametophyte ( n ) Sporophyte Example Gametophyte ( n ) Dominant Dominant Dominant Reduced, dependent on gametophyte for nutrition Mosses and other nonvascular plants Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) PLANT GROUP Gymnosperm Angiosperm Microscopic female gametophytes ( n ) inside ovulate cone Microscopic male gametophytes ( n ) inside pollen cone Sporophyte (2 n ) Sporophyte (2 n ) Microscopic female gametophytes ( n ) inside these parts of flowers Microscopic male gametophytes ( n ) inside these parts of flowers Heterospory: The Rule Among Seed Plants The ancestors of seed plants were likely homosporous, while seed plants are heterosporous Megasporangia produce megaspores that give rise to female gametophytes Microsporangia produce microspores that give rise to male gametophytes Ovules and Production of Eggs An ovule consists of a megasporangium, megaspore, and one or more protective integuments Megasporangium (2 n ) Megaspore ( n ) (a) Unfertilized ovule Integument Spore wall Immature female cone Gymnosperm megaspores have one integument Angiosperm megaspores usually have two integuments Pollen and Production of Sperm Microspores develop into pollen grains , which contain the male gametophytes Pollination is the transfer of pollen to the part of a seed plant containing the ovules Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Male gametophyte (within a germinated pollen grain) ( n ) Female gametophyte ( n ) (b) Fertilized ovule Micropyle Pollen grain ( n ) Spore wall Discharged sperm nucleus ( n ) Egg nucleus ( n ) The Evolutionary Advantage of Seeds A seed develops from the whole ovule A seed is a sporophyte embryo, along with its food supply,...
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This note was uploaded on 06/07/2009 for the course BIOL 05 taught by Professor Helen during the Spring '09 term at UC Riverside.

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seed plants final - Biology 5B Seed Plants Overview:...

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