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Ch 30 - Plant Diversity II (1 slide per page)-1

2 campbell et al 8 derived traits vascular seed

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Unformatted text preview: lar Seed plants Reduced Gametophyte Gymnosperms Sporophyte Sporophyte (2n) (independent) Microscopic male gametophytes (n) inside anthers of flowers (dependent) Se ed No nva sc ula Se ed les s Gametophyte r Degree of Life Stage Microscopic female gametophytes (n) in ovulate cones (dependent) Angiosperms Evolutionary trend towards reduced gametophyte Microscopic male gametophytes (n) in pollen cones (dependent) Sporophyte (2n) (independent) Microscopic female gametophytes (n) inside ovules of flowers (dependent) Reduced gametophyte dependent on sporophyte (seed plants: gymnosperm and angiosperms) (vs. non-vascular plants where sporophyte dependent on gametophyte) Figure 30.2 (Campbell et al) 9 Derived Traits Heterospory Homosporous: • Sporophyte produces 1 kind of spore inside of a sporangium • Germinates into a bisexual (usually) gametophyte • Homospory occurs in most seedless plants Megaspore = female spore Microspore = male spore Figure on page 613 (Campbell et al) Heterosporous • Sporophyte produces one megaspore (♀) inside of each megasporangium and many microspores (♂) inside of each microsporangium • Micro- and megaspores germinate into separate MALE and FEMALE gametophytes • Heterospory occurs in ALL seed plants and a few seedless plants 11 Evolutionary advantages of a miniaturized gametophyte stage: 1. Female gametophyte (which produces the egg) is provided with nutrition by sporophyte 2. Female gametophyte is protected from environmental stress, including desiccation and UV radiation, by sporophyte. 3. No need for water to reproduce since male gametophyte (and its sperm) are so small and can be dispersed by wind long distances in a small capsule (a pollen grain) directly to the female gametophyte. - allows for colonization of dry places...
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