Plant Reproduction
Alternation of Generations
Mosses - gametophyte is the
dominant form of the plant
Ferns, gymnosperms and
angiosperms - sporophyte is the
dominant form of the plant
Sexual reproduction in
angiosperms
Flower parts
sepals - outer whorl or ring
protect the other parts of the
developing flower
petals - next whorl
animal pollinated plants have
brightly colored petals
wind pollinated plants usually
have small or absent
sepals/petals
Stamens - next whorl; male
reproductive structures
consist of:
-anther (produce microspores
that develop into pollen grains)
-filament (supports the anther)
Carpels - innermost whorl; female
reproductive structures
pistil (one or more fused carpels)
-ovary - enlarged base of pistil
-style - stalklike
-stigma -top, sticky or with hairs to
trap pollen grains
Gametophytes develop
within the reproductive
structures
-female gametophyte (embryo sacs) form
within the ovary of the pistil
Megasporangium surrounded by two
integuments, each with a micropyle
-contains a megaspore mother cell,
which undergoes mitosis to produce
four haploid megaspores
-one megaspore undergoes three
mitotic divisions, which produces a cell
with eight haploid nuclei
-one nuclei from each end (pole)
migrate to center and become polar
nuclei
-one cell nearest to micropyle enlarges
and become the egg
-two cells on either side of egg help
attract pollen tube toward the egg
-the integuments and embryo sac are
now a mature ovule, which may
develop into a seed
-male gametophyte (pollen grains) form
within the anthers of the stamens
An anther contains four microsporangia
(pollen sacs)
-microspore mother cells each produce
four haploid microspores
-each microspore undergoes mitosis to
produce two haploid cells that do not
separate (pollen grain)
-the larger of the two cells is the tube
cell (forms pollen tube)
- the smaller of the two cells is the
generative cell, which will divide by
mitosis to form two sperm
Pollination
-occurs when pollen grains are
transferred from an anther to a stigma
-self-pollination - involves one flower,
flowers on the same plant, or flowers
from two genetically identical plants
-cross-pollination - involves two
genetically different plants
-self-pollinated due to structure of flower
-pollen dispersed by water
-pollen dispersed by air (wind)
*depends on:
release of large amounts of pollen
ample air circulation
proximity of plants to which pollen is
transferred
dry weather
-pollinated by animals
-have bright flowers, distinctive
odors, nectar (sugar solution)
-pollinators include bats, bees,
beetles, moths, butterflies,
mosquitoes, monkeys, and
hummingbirds
Fertilization
-union of haploid gametes resulting in
diploid zygote
-a pollen grain must land on a stigma,
absorb moisture, and germinate (form a
pollen tube)
-pollen tube grow through stigma and
style toward the ovary
-enter ovule in ovary through micropyle
-two sperm travel through pollen tube
and reach the egg
-double fertilization is unique to
angiosperms
*one sperm fuses with the egg to form
diploid zygote
*one sperm fuses with two polar nuclei,
and then eventually develops into
endosperm (provides nourishment for
the embryo)
Dispersal of fruits and
seeds
Fruits and seeds are dispersed by:
-animals (carried or eaten)
-wind (tiny or with “parachutes”)
-water (contain air chamber)
-forcible discharge (pod dries and
breaks open)
-gravity
Fruit types
A fruit is a mature ovary.
Fruits protect seeds, aid in their dispersal,
and delay sprouting of seeds.
Classified based on:
-how many pistils or flowers form the
fruit
-whether the fruit is dry or fleshy
p. 619 Table 30-1
Structure of seeds
A seed is a plant embryo surrounded by a
protective coat called the seed coat.
Seed structure differs between monocots,
dicots, and gymnosperms.
-dicot - two cotyledons which store
nutrients (no endosperm)
*plumule - shoot tip with embryonic
leaves
*epicotyl - between plumule and
cotyledons
*hypocotyl - cotyledons to radicle
*radicle - embryonic root
-monocot - one cotyledon and endosperm
*absorbs nutrients from endosperm
-gymnosperm - sporophyte embryo with
needle-like cotyledons, surrounded by
the tissue of the female gametophyte
which functions as a source of nutrients
for the embryo
Seed germination
A seed will not germinate (sprout)
until it is exposed to certain
environmental conditions.
Many seeds experience dormancy (a
state of reduced metabolism;
growth and development do not
occur).
Conditions needed for germination:
-water - softens seed coat, activates
enzymes that convert starch in
cotyledons into simple sugars
-oxygen - needed for cellular respiration
-light - some seeds need light
-temperature - within a certain range
-extreme conditions - pass through
digestive system of animal
Corn (monocot)
1. Appearance of radicle
2. Shoot begins to grow
-cotyledon remains underground
Bean (dicot)
1. Appearance of radicle
2. Hypocotyl curves and becomes
hook-shaped
3. Hypocotyl straightens after it
breaks through the soil
4. Embryonic leaves unfold
(cotyledons shrink and fall off)
Asexual Reproduction
Production of individual without
union of gametes
-clones
-vegetative reproduction (leaves,
stems, roots) - table 30-2 p. 623
Propagation by humans
Cuttings
-roots form from a piece of stem, or
shoots form on a piece of root
(houseplants, ornamental trees and
shrubs, some fruit crops)
Layering
-roots form on stems where they make
contact with the soil (raspberries)
Grafting
-joining of two or more plant parts to
form a single plant
-bud or small stem of one plant is
attached to the roots or stem of a
second plant (vascular cambiums must
be aligned)
-commercial fruit and nut trees, many
ornamental trees and shrubs
Tissue culture
-production of new plants from
pieces of tissue placed on a sterile
nutrient medium
-commercial production of orchids,
houseplants, cut flowers, fruit
plants, and ornamental trees,
shrubs, and nonwoody plants