Transcript Understanding Our Environment

Plant Reproduction
Chapter 42
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Rise of the Flowering Plants
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Virtually all our food is
derived, directly or
indirectly, from flowering
plants.
 Also sources of
medicine, clothing, and
building materials.
Much of early angiosperm
evolution may have taken
place in patches of drier or
unfavorable habitat in the
interior of Gondwanaland.
 Outcrossing may have
been important in early
success.
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Evolution of the Flower
•
Pollen matures within the
anthers and is transported to the
stigma of another flower.

When pollen reaches the
stigma, it germinates, and a
pollen tube grows down,
carrying sperm nuclei to the
embryo sac.
-
Seed matures within
ripening fruit.
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Evolution of the Flower
•
Characteristics
 A complete flower has four
whorls, while an incomplete
flower lacks at least one.
- Calyx, composed of
sepals, makes up
outermost whorl.
- Petals collectively make
up the corolla.
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Evolution of the Flower
Characteristics
Male part:
Stamens collectively compose
androecium.
Stamens made up of filament and
anther.
•
Female part:
Gynoecium refers to the collection
of female parts in a flower.
Single or fused carpels also
referred to as simple or
compound pistils.
Ovules produced in pistil’s
swollen ovary.
Style - Slender neck.
Stigma - Pollen-receptive
structure.
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Evolution of the Flower
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Trends in Floral Specialization
 Separate floral parts have fused.
 Floral Parts have been lost or reduced.
- Resultant of natural selection and
artificial breeding.
Trends in Floral Symmetry
 Many flowers of advanced groups are
bilaterally symmetrical.
- Often associated with advanced
pollination systems.
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Formation of Angiosperm Gametes
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Plant sexual life cycles are characterized by
an alternation of generations.
 Diploid sporophyte gives rise to haploid
gametophyte generation.
- Male gametophytes
(microgametophytes) - Pollen grains
- Female gametophyte
(megagametophyte) - Embryo sac
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Formation of Angiosperm Gametes
•
Angiosperms have separate
structures for reproduction .
Similar to animals, except:

Male and female structures
usually occur together in the
same individual flower.

Angiosperm reproductive
structures are not permanent
parts of the adult individual.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Formation of Angiosperm Gametes
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Pollen Formation
 Each pollen sac contains specialized chambers enclosing
microspore mother cells.
- Undergo meiosis to form four haploid microspores.
 Pollen grain shapes are specialized for specific
flower species.
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Formation of Angiosperm Gametes
•
Embryo Sac
 Megaspore mother cell found within each
ovule.
- Undergoes meiosis to produce four
haploid megaspores.
 Usually only one survives and the other
three are absorbed by the ovule.
 Remaining megaspore undergoes
mitosis and produces eight haploid
nuclei enclosed in an embryo sac.
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Pollination
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Pollination - Pollen is placed on the stigma.
 Early seed plants pollinated passively.
Pollination by Animals
 Bees - Initially locate food sources by odor,
and then orient on a flower by its shape,
color, and texture.
- May drive coevolution.
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Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Pollination
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Other Insects
 Butterflies
 Moths
 Beetles
Birds
 Many plants produce large amount of nectar to
attract birds.
- Hummingbirds
 Red colors tend to attract birds, while
carotenoids tend to attract insects because they
are visible in the UV range.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Pollination
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Other Animals
 Bats
 Rodents
 Monkeys
Wind-Pollinated Angiosperms
 Typically have small, greenish, odorless
flowers with reduced or absent corollas.
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Self-Pollination
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Two basic reasons for self-pollination.
 Ecologically advantageous as they do not
need to be visited by animals, and thus do
not have to expend energy producing
attractants.
 Produces more uniform progeny than
outcrossing.
- Well-adapted to particular habitats.
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Self-Pollination
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Factors Promoting Outcrossing
 Dioecious plants produce only ovules or
only pollen on a single individual.
 Monoecious produce both on same plant.
 Dichogamous - Functional stamens and
pistils present on same plant, but reach
maturity at different times.
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Self-Pollination
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Self-incompatibility results when pollen and
stigma recognize each other as genetically
related and pollen tube growth is blocked.
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Fertilization
Double Fertilization results in two key developments:
 Fertilization of the egg.
 Formation of endosperm.
Pollen grains adhere to the stigma and grow a pollen tube that pierces the style.
 Grows until it reaches the ovule in the ovary.
Tip of pollen tube bursts and releases two sperm cells.
 One fertilizes the egg cell forming a zygote.
 The other cell fuses with two polar nuclei located at the center of the embryo
sac.
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Asexual Reproduction
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Vegetative Reproduction - New plants are
cloned from adult parts.
 Runners
 Rhizomes
 Suckers
 Adventitious Plantlets
Apomixis - Embryos in seeds produced
asexually from the parent plant.
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Life Span of Plants
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Once established, plants live for highly
variable periods of time.
 Life span may or may not correlate with
reproductive strategy.
- Woody plants which have extensive
secondary growth, nearly always live
longer than herbaceous plants, which
have limited to no secondary growth.
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Life Span of Plants
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Annuals
 Annual plants grow, flower, and form fruits
and seeds within one growing season, and
then die when the process is complete.
- Grow rapidly under favorable conditions.
 Developing flowers or embryos use
hormones signaling nutrient
reallocation.
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Life Span of Plants
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Biennials
 Biennial plants have life cycles that take
two years to complete.
- Photosynthate stored in underground
storage organs during the first year.
- Flowering stems are produced during
the second year.
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Life Span of Plants
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Perennials
 Perennial plants grow year after year.
- Majority of vascular plants are perennial.
 Food is often stored in roots or
underground stems which can
become relatively large.
- Trees and shrubs generally flower
repeatedly.
 Deciduous or Evergreen.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Life Span of Plants
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Organ Abscission
 Abscission - Shedding of
leaves or petals.
- Dispense with nutrient
sinks.
 Shaded leaves,
petals
- Evergreens usually have
complete change of
leaves every two to seven
years.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Life Span of Plants
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Abscission involves changes in
abscission zone at the base of
the petiole.
 Young leaves produce
hormones that inhibit
development of specialized
layers of cells in the
abscission zone.
- Cells become
impregnated with suberin.
 Separation layer
develops on the side
of the leaf blade; cells
of the separation
layer divide, swell,
and become
gelatinous.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies