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Chapter 38: Plant Reproduction and Development

Chapter 38: Plant Reproduction and Development. Flowers. Sexual organs of Angiosperms. Develop from compressed shoots with four whorls of modified leaves. Flower Whorls 1. Sepals 2. Petals 3. Stamens 4. Carpels. Sepals. Whorl of sterile leaf-like structures. May be brightly colored.

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Chapter 38: Plant Reproduction and Development

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  1. Chapter 38:Plant Reproduction and Development

  2. Flowers • Sexual organs of Angiosperms. • Develop from compressed shoots with four whorls of modified leaves. • Flower Whorls 1. Sepals 2. Petals 3. Stamens 4. Carpels

  3. Sepals • Whorl of sterile leaf-like structures. • May be brightly colored. • Function • Protect other flower parts. • Attract pollinators.

  4. Whorl of sterile flower parts. Often brightly colored. Function Attract pollinators. Petals

  5. Male reproductive flower structure. Function Produce pollen (sperm). Stamens

  6. Anther - pollen producing sac. Filament - stalk. Stamen Structure

  7. Carpel • Female reproductive flower structure. • Also called pistil. • Function • Produce embryo sac (eggs). • Carpel Structure • Stigma – receives the pollen. • Style – stalk. • Ovary – contains the ovules. • Ovule • A rudimentary seed before fertilization.

  8. Flowers • Are highly variable in form, shape, and color. • Not all flowers contain the same combination of whorls.

  9. Flower Variations • Complete Flowers - have all four whorls. • Incomplete Flowers – less than all four whorls. • Perfect Flowers - have stamens and carpels. • Imperfect Flowers - have stamens or carpels.

  10. Staminate and pistillate flowers are on the same plant. Ex: corn Tassel – staminate flowers Ears – carpellate flowers Monoecious Plants

  11. Dioecious Plants • Have staminate or pistillate flowers, but not both. • Ex: Holly, Ginkgo • Comment - "Seedless" plants may be a staminate plant. • Ex: male Ginkgo

  12. Pollen Development • Pollen is the male gametophyte. • Starts with a 2N cell called a microsporocyte.

  13. Microsporocyte • Undergoes meiosis and produces 4 Microspores (1N). • Each Microspore undergoes mitosis and produces a pollen grain, which is the male gametophyte.

  14. Special cell wall. Tube Nucleus (cell). Generative Nucleus (cell) which will divide and produce two sperm nuclei. Mature Pollen Grain

  15. Embryo Sac Development • The Embryo Sac is the female gametophyte. • Starts with a megasporocyte (2N). • Megasporocyte • Undergoes meiosis and produces 4 Megaspores (1N). • Three of the megaspores abort, leaving only one to develop into the embryo sac.

  16. Megaspore • Undergoes three rounds of mitosis to produce a “sac” with 8 nuclei. • The nuclei may wall off or may remain as part of a large cell. • Embryo Sac • 3 Antipodal cells. • 2 Polar nuclei (1 cell) • 2 Synergid cells • 1 Egg cell

  17. Pollination: The transfer of pollen from a stamen to the stigma. • Pollen Vectors • Bees Flies • Butterflies Moths • Birds Beetles • Bats Wind

  18. The flower is usually highly adapted to the pollen vector. Ex: Colors Rewards Scents Shape Comment

  19. The union of egg and sperm to produce a zygote (2N). Fertilization

  20. Angiosperms • Have double fertilization. 1. Egg + sperm  zygote 2. Polar nuclei + sperm  Endosperm • Endosperm • Is Triploid (3N) tissue that will be used as a nutrition source for the embryo.

  21. After Fertilization • Zygote  Embryo • Ovule  Seed • Ovary  Fruit

  22. Embryo Development • Root/shoot polarity set with 1st cell division. • Mature embryo has all three primary tissues, apical meristems etc. • Endosperm • Monocots - large tissue. • Dicots - transfer the energy over to the embryo's two cotyledons.

  23. Seed Coat • Formed from the integuments of the ovule. • Hard layer to protect the seed. • Fruit • A mature ovary. • Sometimes includes other plant parts. • Ex: apple

  24. Protect the seeds. Aid in seed dispersal. Fruit Types Fleshy: soft ovary walls. Dry: hard ovary walls. Fruit Functions

  25. Fruit Types • Simple Fruit: from a single ovary. • Ex: Peach, Cherry • Aggregate Fruit: from a flower with multiple carpels. • Ex: Raspberry • Multiple Fruit: develops from several flowers into one structure. • Ex: Pineapple

  26. Seeds • Contain a miniature plant. • Main dispersal mechanism for plants. • Embryo is often “dormant” when the seed is mature.

  27. Seed Dormancy • When a seed is not actively growing. • Used to increase the chances that the plant will develop when conditions are favorable. • Usually controlled by plant hormones. • May require changes in temperature, moisture, etc. before growth will continue.

  28. Imbibition • The absorption of water by a seed. • First step in seedling growth. • Causes “swelling” which ruptures the seed coat. • Starts metabolism to resume growth.

  29. Germination • The continuation of growth of the plant within a seed. • Root usually emerges first. • Shoot tip must break through the soil surface.

  30. Role of Light • Light is the usual clue that the shoot has broken above ground. • Light causes many growth changes in the shoot • Ex. Leaves to expand • Stem elongation rate decreases

  31. Asexual Reproduction • Offspring produced by mitosis. • Also called “cloning”.

  32. Fragmentation of the plant body so that new plants are formed. Ex: Cuttings Grafting Offshoots Normal Method

  33. Tissue Culture. Clumps of cells grow into embryoids which can be used to regenerate whole plants. Often used in genetic engineering of plants. High-Tech Methods

  34. Protoplast Fusion. A "naked" plant cell (no cell wall). Used to create new hybrids

  35. Plants • Frequently use both sexual and asexual reproduction depending on the environment. • Asexual - stable • Sexual - unstable

  36. Plant Development • Growth: increase in size • Development: changes in body form and structure. • Plant Problems • Determining the direction of cell growth because of the cell wall.

  37. Control Mechanism • Cytoskeleton: determines the direction of cell expansion. • Cellulose Microfibrils: are arranged in parallel strips as guided by microtubules in the cell membrane.

  38. Cell Expansion • Increase in cell size is usually caused by turgor pressure. • Direction of cell increase is at right angles to the cellulose mircofibrils.

  39. Cell Differentiation • Depends on the control of gene expression. • (review previous chapters on this topic)

  40. The development of specific structures in specific locations. Important in plants since cells don’t usually migrate. Pattern Formation Juvenile Mature

  41. Positional Information • Gradients of chemicals that provide clues of position of cells to each other. • Ex: why some cells develop into shoots and others into roots.

  42. Organ-Identity Genes • Genes for normal organ development. • Used in positional information to determine which organ the cells should develop into.

  43. Example • The combination of three genes that give rise to the flower parts. • A  sepals • A + B  petals • B + C  stamens • C  carpels

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