CHAPTER 30: PLANT DIVERSITY II the evolution of seed plants

Common to all seed plants: - Reduced (miniature) Gametophytes - protects egg-containing gametophytes from environmental stress - enables dependent gametophytes to obtain nutrients from sporophyte - Heterospory - megasporangia -> single, functional megaspore ( female gametophyte) - microsporangia -> vat numbers of microscpores (male gametophyte)

Heterospory.

Common to all seed plants: - Ovules - feamle gametophyte is developed - Pollen - male gametophyte

Gymnosperm evolution -dominance when drier climate favored spread of gymnosperms (Carboniferous ecosystem) -needle-shaped leaves

- angiosperm structure specialized for sexual reproduction - carpel: megasporphyllis (female) - stamen: microsporophyllis (male)

Fruits - Typically consists of ovary, may include other parts - Develops after pollination triggers hormonal changes, causes ovary to grow - wall of ovary: pericarp - seed dispersal: wind, water, animals (cling to fur), edibility (feces)

Angioperm Life Cycle - Double fertilization - 2 sperms : one fertilizes egg, other fuses with two nuclei in the large central cell of the female gametophyte - Divide into endosperm, tissue rich in food reserves - Function: 1)synchronizes development of food storage with development of embryo 2) prevents flowering plants from wasting nutrients on infertile ovules ovule -> seed -> embryo -> root and seed leaves (cotyledons)

Angioperm Life Cycle.

Angiosperms..... Evolution: Archaefructus liagoningenis - closest relative of all angiosperms - mostly male hypothesis: ovules developed on microsporophyllis from mutations in the (separate) pollen producing and ovule producing structures Diversity: Monocots (1 cotyledon) and Eudicots ("true dicots", 2 cotyl.) -basal angiosperms, magnoloids Plant-pollinator relationships - coevolution, both benefit

Human welfare -Use seed plants for food, fuel, wood and medicine -Reliance makes preservation of plant diversity critical -Growing population: threat to plant diversity

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Role of Ovaries and Ovules in flowering plants - The ovary is the structure where seed plants hold their megaspores. A plant can have only one ovary but many ovules as ovules account for the covering of the megaspores within the ovary. The megaspore is protected by tissues called integuments. What appears as a membrane around the megaspore is called a megasporangium. The entire structure protects, and provides nutrients for the megasporum until it is fertilized. The ovary provies an environment where the ovule can thrive as well as mature into a seed.

How many sperm are in a mature pollen grain in the flowering plants? 16,17,18 Each pollen grain has two haploid cells or sperm cells. During fertilization, the sperm nuclei have two fates : Sperm 1- fertilizes egg and forms a diploid zygote Sperm 2- fuses into the large central cell of the female gametophyte This process is called double fertilization which actually only occurs in angiosperms.

What is the chromosome ploidy of the endosperm? and How does it come about? 19 Two endosperms enter the ovule the nuclei endosperm enters the egg- they are haploid cells. Process? Microsporangium are found within the anthers of a flower. Microspores are held in the microsporangium until they are dispersed. The microspores then form pollen grains (which contain the endosperms) Each pollen grain has one endosperm which undergoes meiosis creating two sperm for every generative pollen grain cell.

So, what is the function of an endosperm? 20 Endosperms fertilize the egg of a flower allowing the zygote to grow into a seed. The seed is then able to germinate and grow into a sporophyte plant. Without the sperm, there is a break in the cycle and new generation of sporophyte plants cannot exist.

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