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Chapter 30: Plant Diversity II: The Evolution of Seed Plants. Free-Living Gametophytes. Reduced Gametophytes. Some Seed-Bearing-Plant Anatomy. Megasporangium gives rise (meiotically) to megaspores Integument envelopes, protecting the megasporangium
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Megasporangium gives rise (meiotically) to megaspores • Integument envelopes, protecting the megasporangium • An ovule consists of integument surrounding a megasporangium which in turn surrounds a megaspore • The female gametophyte develops mitotically from the megaspore • The female gametophyte gives rise mitotically to the female gamete, the egg • Once fertilized the egg develops into an embryonic sporophyte • The sporophyte embryo surrounded by the parental megagametophyte which, in turn, is surrounded by grandparental sporophyte tissue is a seed Ovules
Seeds (are complicated) Gametophyte (haploid parent) Sporophyte (next generation) Sporophyte (grandparent)
Gymnosperms Gymnosperms have seeds and vasculature but not flowers nor fruit
Gymnosperms “Gymnosperms are plants that have “naked” seeds that are not enclosed in ovaries. Their seeds are exposed on modified leaves that usually form cones.” p. 593, Campbell & Reece (2005)
Pollen & Heterospory This is pollen!
Pollen freed plants from flagellated sperm so no more need for water for fertilization to take place Pollen & Pollen Tube
Grains of Pollen Seed-bearing plants disseminate their sperm/male gametophyte as pollen Pine pollen
Overall this life cycle takes about three years (not including growth to sexual maturity of the resulting tree) Gymnosperm Life Cycle
Angiosperms Angiosperms are vascular plants that produce seeds via flowers and distribute those seeds via fruit
Male part A Flower Female part
Flying Penises! One of the great advantages of flowering is the potential for pollination by animals
Fruit “A fruit typically consists of a mature ovary, although it can include other flower parts as well…”
“…As seeds develop from ovules after fertilization, the wall of the ovary thickens. A pea pod is an example of a fruit, with seeds (mature ovules, the peas)…” Various Fruits
Even More Fruits “…encased in the ripened ovary (the pod). Fruit protects dormant seeds and aid in their dispersal.” p. 598, Campbell & Reece (2005)
Embryo Sac: 7-Cell Gametophyte Synergids …antipodal cells… Egg Double fertilization is of these two cells Formation of embryo sac: the angiosperm female gametophyte Polar Nuclei