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Plant Reproduction

Plant Reproduction. AP Biology Unit 5. Alternation of Generations. All land plants can exist in two different multicellular forms Sporophyte (2n) Gametophyte (n) In a life cycle, plant generations alternate between sporophyte and gametophyte Each form gives rise to the other form.

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Plant Reproduction

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  1. Plant Reproduction AP Biology Unit 5

  2. Alternation of Generations • All land plants can exist in two different multicellular forms • Sporophyte (2n) • Gametophyte (n) • In a life cycle, plant generations alternate between sporophyte and gametophyte • Each form gives rise to the other form

  3. Sporophyte vs. Gametophyte • Sporophyte (2n) • Diploid, multicellular form of a plant • Forms haploid spores through meiosis • Gametophyte (n) • Haploid, multicellular form of a plant • Forms gametes through mitosis

  4. Alternation of Generation

  5. How is this different from other organisms? • In other organisms (like humans) the haploids are unicellular (sperm and egg) • In plants both forms (sporophyte and gametophyte) can be multicellular

  6. Evolution of Plant Reproduction • Each type of plant has a dominant form (sporophyte or gametophyte) • Dominant form = the “plant” we think of • As plants have evolved, there have been changes to relationship between sporophyte and gametophyte

  7. Gametophyte/Sporophyte Relationships • 3 different possibilities • Larger gametophyte, sporophyte is dependent on it • Larger sporophyte, gametophyte is independent • Larger sporophyte, gametophyte is dependent

  8. Question… • What trend do you see between the evolution of plants (from nonvascular  vascular; nonseed  seed plants) and the alternation of generations? • As plants have evolved, the gametophyte has become more reduced, sporophyte has become more dominant

  9. Reproductive Organs • Archegonium • Female sex organ  produces egg • Antheridium • Male sex organ  produces sperm

  10. Vascular Plants: Homosporous vs. Heterosporous • Vascular plants have sporophylls • modified leaves that produce sporangia (which become spores) • Homosporous plants • Most ferns • Heterosporous plants • All seed plants (angiosperms and gymnosperms) and some seedless plants

  11. Water vs. Wind • Mosses and Ferns require water to help the sperm reach the egg. • Seed plants no longer require water to reproduce • Pollen (male gametophyte) can be carried by wind, animals, etc.

  12. Gymnosperm Life Cycle • Sporophyte is the dominant form • Heterosporous • Have “naked” seeds – nothing around the seed • Cones are either male (contain pollen) or female (contain ovule)

  13. Flower Anatomy • The flower is the reproductive organ of an angiosperm • Female part = Carpel • Consists of the stigma, style, and ovary • Male part = Stamen • Consists of anther and filament

  14. Angiosperms • Dominant form is the sporophyte • Heterosporous • Male gametophyte = pollen grain • Female gametophyte = embryo sac

  15. Female Gametophyte • The megaspore will go through MITOSIS to create a series of different cells in the female gametophyte • Cells involved in fertilization are • Egg (n)– haploid • Polar nuclei (2n) – 2 nuclei in one cell

  16. When the pollen grain lands on the stigma, it will extend a pollen tube down the style to get to the egg Specific cells in the pollen tube go through mitosis to form 2 sperm Sperm will enter

  17. Double Fertilization • Angiosperm fertilization actually consists of 2 separate fertilization events = double fertilization • Both sperm in the pollen tube are used • One sperm fertilizes the egg  diploid zygote (2n) forms • The other sperm fertilizes the polar nuclei (2n)  forms triploid endosperm (3n)

  18. Double Fertilization • Double fertilization is unique to angiosperms • Through this process, resources are used most efficiently since endosperm can only develop in a fertilized ovule. • Endosperm = starchy material that serves as nutrition for the growing embryo

  19. Other Post-Fertilization events • Embryo develops (diploid) • Seed coat forms • Ovary develops into fruit around the seed

  20. Germination and Seedling Formation • Seeds are dormant until they begin germination • When conditions are right, seeds will begin to germinate to form a seedling. • Germination starts with imbibition—when water enters the seed and triggers enzymes that are needed for growth.

  21. Seed Benefits • What are the evolutionary benefits of seeds? • Dispersal- embryo can travel far from parent • Protection- seed coat protects embryo • Dormancy- can wait until conditions are favorable to germinate • Storage- food for the embryo can be stored inside seed (ex. endosperm)

  22. Monocots vs. Eudicots • Most angiosperms can be classified as either Monocots or Eudicots

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