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Chapter 31 Plant Reproduction


									Plants reproduce sexually, often relying
on pollinators to bring sperm and egg
The sporophyte (diploid) develops from
the zygote by mitosis; it consists of
roots, stems, leaves, and flowers
Meiosis of cells within flowers produces
the small haploid gametophytes, which
in turn produce either sperm or eggs.
 The specialized parts of the flower grow
  from the modified end of the floral shoot –
  the receptacle.
    Sepals: (collectively called the calyx) are
     the outermost green, leaflike parts.
    Petals (collectively called the corolla) are
     the colored parts of located between the
     reproductive structures and the sepals.
 Flowers differ from the other tissues of
  the plant in their fragrance and colors
  (Carotenoids and anthocyanins), which
  are attractive to pollinators.
 Male parts – called stamens are located
  inside the corolla
   Stamen consist of a slender stalk (filament)
    capped with an anther
   Inside the anthers are pollen sacs in which pollen
    grains develop

   Look at the previous picture to see the male parts
    in a diagram
 Female parts are located in the central part of
  the flower
   Carpel is the vessel-shaped structure with an
    expanded lower chamber (ovary), slender column
    (style) and upper surface (stigma) for pollen
   In ovary eggs develop, fertilization occurs and
    seeds mature.

   Refer to diagram
 Perfect flowers have both male and female
  parts (may or may not be on the same plant)
 Imperfect flowers is missing one of the sex
 In anthers, each diploid “mother” cell divides by
  meiosis to form four haploid microspores.
 Each microspores will divide to form pollen
 One cell in each pollen grain will produce the
  sperm; the other will form the pollen tube
 In carpel, a mass of tissue forms an ovule (potential
  seed) enclosed by integuments.
 A diploid “mother” cells divides by meiosis to produce
  haploid megaspores, one of which will undergo mitosis
  three times to produce a cell with eight nuclei
 The nuclei migrate resulting in an embryo sac (female
  gametophyte) with seven cells; one cell has two nuclei
  and will become the endoperm (nutrition for embryo);
  another cell will be the egg
 Pollination is the transfer of pollen to the surface
  of the stigma by the actions of insects, birds, or
  other agents.
 In germination, a pollen tube forms producing a
  path that the two sperm will follow to the ovule.
 When the pollen tube reaches an ovule, it
  penetrates the embryo sac, and the two sperm
  are released.
   One sperm fuses with the egg nucleus to form a
    diploid zygote
   The other sperm nucleus fuses with the two
    endoperm nuclei to yield a triploid “Primary
    endosperm cell” that will nourish the young
    sporophyte seedling.
 The zygote undergoes repeated divisions to
  form an embryo sporophyte as a part of an ovule
  and is accompanied by formation of fruit.

 Cotyledons (seed leaves) develop for the
  purpose of utilizing the endosperms during
 From zygote to embyro, the plant supplies
  nutrition until the time when the connection
  between the ovule and ovary wall is broken
 The mature ovule integuments thicken inot seed
  coats around the seed (a mature ovule
  containing embryo and food reserve)
 Embryo is inactive
 Seed dehydrates (5 -15% water)
 Embryo surrounded by endosperm, enlarged
  cotyledons or both
 A fruit mature ovary with seeds (ovules) inside;
  they may be classified as simple aggregate,
  multiple or accessory.
 The pericarp of a fruit consists collectively of
  endocarp (around the seed), mesocarp (fleshy
  portion), and exocarp (the skin)
 Immature fruit protects the seed (green, bitter,
  sour, etc.)
 Mature fruit aids in dispersal (colorful and tasty)
 Forms from ovary
 Does not provide nutrient for seeds
 Seeds have coevolved with particular dispersing
  agents – currents of air or water, or animals passing
   Example: Pericarp of maple seeds extends out like wings
    to catch the wing and be transported
   Some fruits are dispersed by sticking on animal bodies or by
    passing through the digestive tract to be deposited in the
 Humans are perhaps the grand dispersing agents by
  virtue of the long distances to which they carry seeds
 Seed frequently undergo a period of dormancy.
 Requires water, oxygen, and warm temperatures
 Root emerges first. WHY AGAIN?
 Vegetative growth modes includes: runners,
  rhizomes, corms, tubers, and bulbs.
 Parthenogenesis, embryo development from an
  unfertilized egg, can produce new orange plants.
 Vegetative propagation (“Cuttings”) can result in
  new plants produced from leaves that form
 Tissue Culture propagation can result in whole
  plants produced from a group of cells.

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