Homospory vs. Heterospory The principal difference between homospory and heterospory is the separation of sexes at different points in the life cycle, –female gametes in ovules, –male gametes in pollen grains, heterospory promotes outcrossing among plants, since microspores may drift farther from the sporophyte than megaspores.
Ferns vascular diploid dominant homosporous motile gametes seedless + water dependent Branched sporophyte not dependent on gametophyte at maturity. reduced, naked... Fig. 29.23
Sporophyte vs. Gametophyte self defense, anti-desiccant, large, branched sporophyte capable of producing more spores, diploid organism has a greater capacity for complex growth, –two copies of every gene, haploid diploid –mutation do not necessarily hinder development (i.e. one good copy and one mutant copy in a diploid). w/ mutant gene
Heterosporous “primitive” In these plants, a sporophyte produces two types of sporangia, –microsporangia contain microspore mother cells, each of which undergoes meiosis, forming microspores, –megasporangia contain megaspore mother cells, each of which undergoes meiosis, forming megaspores. Selagenella microsporangia megasporangia sporophyll: (phyll: leaf)
Gymnosperms vascular diploid dominant heterosporous nonmotile gametes naked seeds not water dependent
Gymnosperm Seeds naked embryos Ovule (immature): megasporangium “surrounded” by integument. When mature, an ovule becomes a seed.
Pollen gymnosperms Outer layer of pollen is made impermeable by a cyclic alcohol “sporopollenin”, –winged for wind dispersal, –lots of pollen is produced, and randomly reaches the micropyle of receptive ovules. Lodgepole pine Pinus contorta
Angiosperms vascular diploid dominant heterosporous nonmotile gametes seeds w/ 3n endosperm not water dependent
Monocots/Dicots Monocot: Petals are in multiples of three Leaf veins run parallel Vascular bundles in the stem are dispersed Dicot: Petals are in multiples of four or five Leaf veins are branched Vascular bundles in the stem are arranged in a ring
Corn is a fruit! Types of fruit: Simple = single flower, single ovary Aggregate = single flower, multiple ovaries Multiple = multiple flowers, ovaries fuse together A fruit is a mature ovary that develops after the egg has been fertilized. Each kernel is a simple fruit