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.