Chap. 4 plant reproduction final
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  • 1. Chapter 4. Plant Reproduction KEY CONCEPT All plants alternate between two phases in their life cycles. AP Biology 2005-2006
  • 2. Plant life cycles alternate betweenproducing spores and gametes.  A two-phase life cycle is called alternation of generations.  haploid phase  diploid phase  alternates SPOROPHYTE PHASE between fertilization the two GAMETOPHYTE meiosis PHASEAP Biology
  • 3. Animal vs. Plant life cycle Animal Plant multicellular multicellular sporophyte 2n 2n gametes spores 1n 2n unicellular multicellular gametes gametophyte 1n 1nAP Biologyalternation of generations
  • 4. Alternation of generations diploid haploidAP Biology 2005-2006
  • 5. Evolutionary trends  Alternation of generations  dominant haploid plant  bryophytes - mosses  dominant diploid plant  pteridophytes - ferns  gymnosperm - conifers  angiosperm - flowering plants  Evolutionary advantage?  reduction of gametophyte protects delicate egg & embryo in protective sporophyte AP Biology
  • 6. Gametophytes of seed plants Gymnosperm Angiosperm  male gametophyte  male gametophyte  pollen in male cone  pollen in anthers of flower  female gametophyte  female gametophyte  develops in female  develops in ovaries cone of flower  seed  seed  naked in cone  protected in ovary  ovary wall can develop into fruitAP Biology
  • 7.  The sporophyte is the dominant phase for seed plants.AP Biology
  • 8. Gymnosperm life cycle female gametophyte in cone male gametophyte in pollen sporophyte in seedAP Biology
  • 9. Angiosperm life cycle male gametophyte in pollen female gametophyte in ovary sporophyte in seed AP Biology
  • 10. Reproduction in angiosperm  Sporophyte plant produces unique reproductive structure = the flower  male gametophyte = pollen grain  develop within anthers of flower  female gametophyte = embryo sac  develop within ovaries of flower  pollination by wind or animals brings pollen grain to female gametophyte  fertilization takes place within ovary  double fertilization = embryo & endosperm  seeds contain sporophyte embryo  development of seeds in ovary  ovary develops into fruit around the seedAP Biology
  • 11. FlowersAP Biology
  • 12. Flower  Modified shoot with 4 rings of modified leaves  sepals  petals  stamens  male  carpals  femaleAP Biology
  • 13. Male & female parts of flowerAP Biology
  • 14. Parts of flower  Male  stamens = male reproductive organs  stamens have stalks (filament) & terminal anthers which carry pollen sacs  pollen sacs produce pollen  pollen grain = gametophyte  sperm-producing structureAP Biology
  • 15. Parts of flower  Female  carpels = female reproductive organs  ovary at the base  slender neck = style  within the ovary are 1 or more ovules  within ovules are embryo sacs  female gametophyte = embryo sac  egg-producing structure AP Biology
  • 16. Fertilization in Angiosperms  When pollen grain lands on stigma it begins to grow pollen tube.  Nucleus within pollen grain divides and forms 2 sperm nuclei  Pollen tube contains tube nucleus and 2 sperm nuclei  Pollen tube grows into style and eventually reaches ovary and enters ovule AP Biology
  • 17. Fertilization in Angiosperms  Inside embryo sac, two fertilizations occur  One sperm nuclei fuses with egg nucleus to produce diploid zygote – grows into plant embryo  Second sperm nucleus fuses with two polar nuclei to form triploid (3N) cell – food tissue known as endosperm. AP Biology
  • 18. stigma embryo sac pollen tube endosperm (3n) ovary zygote (2n) ovule micropyleAP Biology
  • 19. Fertilization (recap)  Pollination  pollen released from anthers is carried by wind or animals to land on stigma  pollen grain produces a pollen tube  pollen tube grows down style into ovary & discharges 2 sperm into the embryo sac  1 sperm fertilizes egg = zygote  zygote develops into embryo  ovule develops into a seed  ovary develops into a fruit containing 1 or more seedsAP Biology
  • 20. Pollination “syndromes” Butterfly Hummingbird Generalist Hawk moth Bee AP Biology
  • 21. Self-pollinationWhy? Guarantees seeds (no need for mates or pollinators) May save resources if flowers are smaller Maximizes transmission of own genesWhy not? Inbreeding depression - short-term cost Loss of genetic diversity - long-term cost An evolutionary dead end? - very long-term costAP Biology
  • 22. Preventing self-pollination  Various mechanisms  stamens & carpels may mature at different times  arranged so that animal pollinator won’t transfer pollen from anthers to stigma of same flower  biochemical self-incompatibility = block pollen tube growth AP Biology
  • 23. Fertilization takes place within theflower. Male gametophytes, or pollen grains, are produced in the anthers. – male spores produced in anthers by meiosis – each spore divides by mitosis to form two haploid cells – two cells form a single pollen grain pollen grain AP Biology
  • 24. One female gametophyte can form in each ovule of a flower’s ovary.  four female spores produced in ovule by meiosis  one spore develops into female gametophyte  female gametophyte contains seven cells  one cell has two nuclei, or polar nuclei  one cell will develop into an eggAP Biology
  • 25.  Pollination occurs when a pollen grain lands on a stigma. pollen tube sperm stigma – one cell from pollen grain forms pollen tube – other cell forms two sperm that travel down tube AP Biology
  • 26.  Flowering plants go through the process of double fertilization. female gametophyte egg sperm polar nuclei ovuleAP Biology
  • 27. Flowering plants go through the process of double fertilization. endosperm – one sperm fertilizes the egg seed coat – other sperm unites with polar nuclei, forming endosperm – endosperm provides food supply for embryo embryo AP Biology
  • 28.  Each ovule becomes a seed. The surrounding ovary grows into a fruit. AP Biology
  • 29. Fertilization in flowering plants  Double fertilization  2 sperm from pollen  1 sperm fertilizes egg = diploid zygote  1 sperm fuses with 2 polar nuclei to form 3n endosperm  endosperm = food tissue in seed  coconut milk  grainsAP Biology
  • 30. Fertilization in flowering plants  Development of the new sporophyte AP Biology
  • 31. Plant embryo endosperm seed coat cotyledons ovary wall embryoAP Biology
  • 32. Fruit  Fruit is a mature ovary  seeds develop from ovules  wall of ovary thickens to form fruit  fruits protect dormant seeds & aid in their dispersalAP Biology
  • 33. Seed dispersal • Why disperse?AP Biology
  • 34. Seed dispersal • Why disperse? • sample more (better?) sites for germination/growth • avoid predation or disease • avoid competitionAP Biology
  • 35. Seed dispersal  Plants produce enormous numbers of seeds to compensate for low survival rate  a lot of genetic variation for natural selection to screenAP Biology 2005-2006
  • 36. Seeds and Seed GerminationAP Biology
  • 37. Seed structureAP Biology
  • 38. Seed DormancyAP Biology
  • 39. Dormancy  Metabolism falls  Number of organelles per cell falls  Dehydration – water content falls  Vacuoles in cells deflate  Food reserves become dense crystalline bodiesAP Biology
  • 40. Maintaining dormancy  Physical barriers The seed coat (testa) is waxy = waterproof and impermeable to oxygen  Physical state – dehydrated  Chemical inhibitors present e.g. salts, mustard oils, organic acids, alkaloids  Growth promoters absentAP Biology
  • 41. Seed viability  Viability: When a seed is capable of germinating after all the necessary environmental conditions are met.  Average life span of a seed 10 to 15 years.  Some are very short-lived e.g. willow (< 1 week)  Some are very long-lived e.g. mimosa 221 years  Conditions are very important for longevity  Cold, dry, anaerobic conditions  These are the conditions which are maintained in seed banksAP Biology
  • 42. Germination: The breaking of dormancyThe growth of the embryo and its penetration of the seed coat Break down of barriers Abrasion of seed coat (soil particles) Decomposition of seed coat (soil microbes, gut enzymes) Cracking of seed coat Change in physical (fire) state - rehydration Destruction and dilution of inhibitors Light, temperature, water Production of growth AP Biology promoters
  • 43. Seeds begin to grow whenenvironmental conditions are favorable.  Seed dormancy is a state in which the embryo has stopped growing. – Dormancy may end when conditions are favorable. – While dormant, embryo can withstand extreme conditions. AP Biology
  • 44. Seed GerminationAP Biology
  • 45.  Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat – embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to embryo AP Biology
  • 46.  Germination begins the growth of an embryo into a seedling.  water causes seed to swell and crack coat  embryonic root, radicle, is first to emerge  water activates enzymes that help send sugars to embryo – embryonic shoot, plumule, emerges nextAP Biology
  • 47.  Germination begins the growth of an embryo into a seedling.  water causes seed to swell and crack coat  embryonic root, radicle, is first to emerge  water activates enzymes that help send sugars to embryo  embryonic shoot, plumule, emerges next – leaves emerge lastAP Biology
  • 48.  Once photosynthesis begins, the plant is called a seedling. AP Biology
  • 49. Germination STAGE EVENTSPREGERMINATION (a) Rehydration – imbibition of water. (b) RNA & protein synthesis stimulated. (c) Increased metabolism – increased respiration. (d) Hydrolysis (digestion) of food reserves by enzymes. (e) Changes in cell ultra structure. (f) Induction of cell division & cell growth.GERMINATION (a) Rupture of seed coat. • Emergence of seedling, usually radicle first.POST GERMINATION (a) Controlled growth of root and shoot axis. (b) Controlled transport of materials from food stores to growing axis. (c) Senescence (aging) of food storage tissues.AP Biology
  • 50. Any Questions??AP Biology
  • 51. Aaaaah… Structure-Function yet again!AP Biology