Plants and Pollinators

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Transcript Plants and Pollinators

Plant Reproduction and
Development
Chapter 28
Angiosperm
Life Cycles
• Dominant form is the
diploid sporophyte
mature
sporophyte
seed
• In flowers, haploid
spores formed by
meiosis develop into
gametophytes
fertilization
DIPLOID
HAPLOID
meiosis
(within
anther)
meiosis
(within
ovary)
gametes
(sperm)
microspores
(mitosis)
male
gametes
gametophyte
megaspores
(eggs)
(mitosis)
female
gametophyte
Flower
Structure
STAMEN
(male reproductive part)
filament
anther
CARPEL
(female reproductive part)
stigma
style
ovary
• Nonfertile parts
– Sepals
– Receptacle
• Fertile parts
– Male stamens
– Female carpels
ovary)
OVULE
(forms
within
ovary)
petal (all petals
combined are the
flower’s corolla)
sepal (all sepals
combined are the
flower’s calyx)
receptacle
Kinds of Flowers
• Perfect flowers
– Have both male and female parts
• Imperfect flowers
– Are either male or female
– Same plant may have both male and
female flowers
– Sexes may be on separate plants
Pollen Formation
• Each anther has four pollen sacs
• Inside the pollen sacs, cells undergo
meiosis and cytoplasmic division to form
microspores
• Microspores undergo mitosis to form
pollen grains
Egg Formation
• Ovules form inside the ovary of a flower
• Protective integuments form around the ovule
• Inside, cells divide by meiosis to form haploid
megaspores
• All megaspores but one disintegrate
Pollination
• Transfer of pollen grains to a receptive stigma
• Pollen can be transferred by a variety of
agents
• When a pollen grain lands on the stigma it
germinates
Seed Formation
• Fertilization of the egg produces a diploid
sporophyte zygote
• The zygote undergoes mitotic divisions to
become an embryo sporophyte
• Seed: A mature ovule, which encases an
embryo sporophyte and food reserves
inside a protective coat
Structure of a Seed
• Protective seed coat is derived from
integuments that enclosed the ovule
• Nutritious endosperm is food reserve
• Embryo has one or two cotyledons
– Monocot has one
– Dicot has two
Seed Dispersal
• Fruit structure is adapted to mode of dispersal
• Some modes of seed dispersal:
– Wind currents
– Water currents
– Animals
Asexual Reproduction
• New roots or shoots grow from
extensions or fragments of existing plants
• Proceeds by way of mitosis
• All offspring are genetically identical
(unless mutation occurs)
Natural Clones
• Forest of Quaking Aspen in Utah
– 47,000 trees are genetically identical shoots
– Roots are all interconnected
• Oldest known clone
– Ring of Creosote bushes in Mojave desert that is
11,700 years old
Seed Germination
• Process by which the plant embryo
resumes growth after seed dispersal
• Depends upon environmental factors
– Temperature
– Soil moisture
– Oxygen levels
Splitting the Seed Coat
• Imbibition
– Water molecules move
into a seed
• As water moves in, the
seed swells and the
coat ruptures
Growth of a Bean Plant
primary leaf
hypocotyl
two
cotyledons
primary
root
branch
root
Growth of a Corn Plant
Hormones and Development
• Genes governing the synthesis of
hormones are activated in some cells
but not others
• This can start different cell lineages
down different developmental pathways
• Hormones interact with other gene
products and with the environment to
affect growth and development