Chapter 30 – Plant Diversity II:  Chapter 30 – Plant Diversity II:  The Evolution of Seed PlantsThe Evolution of Seed Plants

I.  Overview of seed plant evolution There were three (3) major reproductive adaptations in the evolution of seed plants

A.  Reduction of the gametophyte continued with the evolution of seed plants

1.  In seed plants, the very small female gametophyte develops from spores retained in the sporangia of the sporophyte. Why??

a.  Delicate female gametophytes are protected from environmental stress. Nourished by the sporophyte.

b.  Embryos that are produced are also protected from drought and UV radiation.                       

2.  Gametophytes of seed plants are microscopic, so they can exist within the sporophyte.

 

Figure 30.1c (p. 598, ed. 6; Fig. 30.2, p.592, ed. 7) – Three variations on gametophyte/sporophyte relationships.

B.  Seeds became an important means of dispersal                        1.  Seeds are resistant to environmental stress, multicellular, complex structures that consist of a sporophyte embryo, a food supply, and a protective coat. 2.  The embryo develops from the spore retained within the sporangium. 

 3.  All seed plants are heterosporous Female spores give rise to female gametes; male spores give rise to male gametes.                                    a.  The megasporangia produce megaspores (female) and the microsporangia produce microspores (male). 4.  The megasporangium is enveloped by layers of tissue called integuments.  The whole structure (integuments + megasporangium) is called the ovule.  Figure 30.2 (p. 599) – From ovule to seed (ed. 6); Fig. 30.3, p. 593, Ed. 7). **Know the structures and sequence in Figure 30.2**

            C.  Pollen (Sperm cells) eliminated the liquid-water requirement for fertilization                        1.  Pollen travels by air or on animals.  It eliminates the need for water to be present during fertilization.

D.  Two clades of seed plants Figure 30.4 (p. 601) – Hypothetical phylogeny of the seed plants.                                      

II.  Gymnosperms            A.  Mesozoic era was the age of gymnosperms1.  Gymnosperms were the most common plants during the Mesozoic era (the age of dinosaurs).             B.  Four phyla of extant gymnosperms Figure 30.5 (p. 602) – Phylum Ginkgophyta:  Ginkgo biloba.Figure 30.6 (p. 602) – Phylum Cycadophyta: cycads.Figure 30.7 (p. 603) – Phylum Gnetophyta.Figure 30.8 (p. 604) – Phylum Coniferophyta:  A sampling of conifer diversity.  **Know the common names of phyla discussed**

For ed. 7 - Fig. 30.4, p. 394-5.

1.  Gymnosperms are vascular plants that bear naked seeds – seeds not enclosed in specialized chambers. 

      Examples:  Ginkgo, Cycads, Gnetophyta (Welwitschia, Gnetum, Ephedra), and Conifers (Common names)

            C.  Life cycle of a pine demonstrates the key reproductive adaptations of seed plants                        Figure 30.9 (p. 605, ed 6; Fig. 30.6, p. 597, ed. 7) – The life cycle of a pine.              

1.  The tree is the sporophyte. 2.  Female gametophyte develops within the sporangium. 3.  Pollen cone has microsporangium that develops into pollen (male gametophyte). 4.  After fertilization, the embryo develops and is surrounded by food reserves and a seed coat. 5.  Embryo grows to produce a new sporophyte.

2.  Angiosperms are flowering plants that form seeds inside a protective chamber called an ovary.

                                   A.  Systematists are identifying angiosperm clades                        1.  Monocots are angiosperms that possess one embryonic seed leaf (cotyledon). 2.  Dicots are angiosperms that possess two embryonic seed leaves (cotyledons). 3.  However, Angiosperms are still being divided into new taxonomic groups as we learn more about them.

B.  The flower is the defining reproductive adaptation of angiosperms                        1.  Flowers are made up of four types of modified leaves sepals, petals, stamens, and carpels.                                    a.  Stamens are the male reproductive organs that produce microspores. b.  Carpels are female reproductive organs that produce megaspores. Figure 30.13 (p. 608, ed. 6; Fig. 30.7, p. 598, ed.7) – The structure of a flower.                                    **Know the different flower parts**

 2.  A fruit is a mature ovary                                   a.  Protect dormant seeds. b.  Fruit aids in seed dispersal.                     - Wind dispersal                     - Attachment and transportation                     - Consumption – berries contain seeds to be passed in feces Figure 30.16 (p. 609) – Fruit adaptations that enhance seed dispersal.

            C.  Life cycle of an angiosperm                        1.  Mature plant is the sporophyte 2.  Some plants easily self-pollinate, but most have mechanisms to ensure cross-pollination.   3.  Male gametophytes reach female gametophytes by producing a pollen tube.      Figure 30.17 (p. 611, ed.6; Fig. 30.10, p. 600, ed.7) – The life cycle of an angiosperm.

 D.  Angiosperms dominated the earth at the end of the Mesozoic era                        1.  Radiation of angiosperms represents the transition from Mesozoic to Cenozoic E.  Angiosperms and animals have affected one another’s evolution                        1.  Coevolution is the mutual influence on the evolution of two different species interacting with each other and reciprocally influencing each other’s adaptations.                                    a.  Pollinator-plant relationships

IV.  Plants and Human Welfare

A.  Agriculture is almost totally dependent on angiosperms             B.  Plant diversity is a nonrenewable resource                        1.  Many medicines are obtained from plant materials Table 30.2 (p. 613) – A sampling of medicines derived from plants. 

 2.  Deforestation eliminates Biodiversity, which cannot be regained.