Transcript 22.1 Plant Life Cycles

22.1 Plant Life Cycles
KEY CONCEPT
All plants alternate between two phases in their life
cycles.
22.1 Plant Life Cycles
Plant life cycles alternate between producing spores and
gametes.
• A two-phase life cycle is called alternation of generations.
– haploid phase
– diploid phase
– alternates between
the two
SPOROPHYTE
PHASE
fertilization
meiosis
GAMETOPHYTE
PHASE
22.1 Plant Life Cycles
• The spore-producing plant is the mature sporophyte.
– sporophyte phase is diploid
– begins with fertilized egg
– spores produced through
meiosis
• The gamete-producing plant is the
mature gametophyte.
– gametophyte
phase is haploid
– begins with spore
– gametes
produced through
mitosis
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Life cycle phases look different among various plant
groups.
• Nonvascular plants have a dominant gametophyte phase.
– moss gametophytes look like green carpet
– moss sporophytes shoot up as stalklike structures
sporophyte (2n)
capsule
spores (1n)
gametophyte (1n)
22.1 Plant Life Cycles
• The sporophyte is the dominant phase for seedless
vascular plants.
– Fern spores form in sacs, sori, on underside of mature
sporophytes (fronds).
sporophyte (2n)
sori
22.1 Plant Life Cycles
– A fern gametophyte, or prothallus, produces sperm and
eggs.
gametophyte (1n))
rhizoid
– A zygote forms on the prothallus, growing into the
sporophyte.
22.1 Plant Life Cycles
• The sporophyte is the dominant phase for seed plants.
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pine trees are typical seed plant sporophytes
female spores produced in female cones
male spores produced in male cones
male spores develop into pollen grains, the male
gametophytes
female spores develop into female gametophytes that
produce eggs
sperm from pollen travel down pollen tube toward egg
fertilized egg develops into embryo
ovule develops into protective pine seed
22.1 Plant Life Cycles
• The sporophyte is the dominant phase for seed plants.
22.1 Plant Life Cycles
KEY CONCEPT
Reproduction of flowering plants takes place within
flowers.
22.1 Plant Life Cycles
Flowers contain reproductive organs protected by
specialized leaves.
• Sepals and petals are modified leaves.
– Sepals are outermost
layer that protects
developing flower
sepal
22.1 Plant Life Cycles
– Petals can help to attract animal pollinators
petal
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• A stamen is the male structure of the flower.
stamen
filament
anther
– anther produces pollen grains
– filament supports the anther
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• The innermost layer of a flower is the female carpel.
stigma
carpel
style
ovary
– stigma is sticky tip
– style is tube leading from stigma to ovary
– ovary produces female gametophyte
22.1 Plant Life Cycles
Flowering plants can be pollinated by wind or animals.
• Flowering plants pollinated when pollen grains land on
stigma.
• Wind pollinated flowers have small flowers and large
amounts of pollen.
22.1 Plant Life Cycles
• Animal pollinated flowers have larger flowers and less
pollen.
– many flowering plants pollinated by animal pollinators
pollen grains
– pollination occurs as animal feeds from flower to flower
– animal pollination more efficient than wind pollination
22.1 Plant Life Cycles
Fertilization takes place within the flower.
• Male gametophytes, or pollen grains, are produced in the
anthers.
– male spores produced in
anthers by meiosis
– each spore divides by
mitosis to form two
haploid cells
– two cells form a
pollen grain
single pollen grain
22.1 Plant Life Cycles
• One female gametophyte can form in each ovule of a
flower’s ovary.
– four female spores produced in ovule by meiosis
– one spore develops into female gametophyte
– female gametophyte contains seven cells
– one cell has two nuclei, or polar nuclei
– one cell will develop into an egg
22.1 Plant Life Cycles
• Pollination occurs when a pollen grain lands on a stigma.
pollen tube
sperm
stigma
– one cell from pollen grain forms pollen tube
– other cell forms two sperm that travel down tube
22.1 Plant Life Cycles
• Flowering plants go through the process of double
fertilization.
female
gametophyte
egg
sperm
polar nuclei
ovule
22.1 Plant Life Cycles
• Flowering plants go through the process of double
endosperm
fertilization.
– one sperm fertilizes
the egg
seed coat
– other sperm unites
with polar nuclei,
forming endosperm
– endosperm provides
food supply for
embryo
embryo
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• Each ovule becomes a seed.
• The surrounding ovary grows into a fruit.
22.1 Plant Life Cycles
KEY CONCEPT
Seeds disperse and begin to grow when conditions are
favorable.
22.1 Plant Life Cycles
Animals, wind, and water can spread seeds.
• Seeds dispersed by animals can have nutritious fruits or
fruits that cling.
22.1 Plant Life Cycles
• Seeds dispersed by wind can have wing- or parachutelike fruits.
Cypselae
Double samaras
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• Seeds dispersed by water can have fruits that float.
22.1 Plant Life Cycles
Seeds begin to grow when environmental conditions are
favorable.
• Seed dormancy is a state in which the embryo has stopped
growing.
– Dormancy may end
when conditions are
favorable.
– While dormant,
embryo can withstand
extreme conditions.
22.1 Plant Life Cycles
• Germination begins the growth of an embryo into a
seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
22.1 Plant Life Cycles
• Germination begins the growth of an embryo into a
seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
– embryonic shoot, plumule, emerges next
22.1 Plant Life Cycles
• Germination begins the growth of an embryo into a
seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
– embryonic shoot, plumule, emerges next
– leaves emerge last
22.1 Plant Life Cycles
• Once photosynthesis begins, the plant is called a seedling.
22.1 Plant Life Cycles
KEY CONCEPT
Plants can produce genetic clones of themselves
through asexual reproduction.
22.1 Plant Life Cycles
Plants can reproduce asexually with stems, leaves, or
roots.
• Asexual reproduction allows a plant to make copies of itself.
• Regeneration is one type of asexual reproduction.
– plants grow a new individual from fragment of parent
– occurs when piece of a stem, leaf, or root falls off parent
plant
22.1 Plant Life Cycles
• Vegetative reproduction is another type of asexual
reproduction.
– stems, leaves, or roots
attached to parent plant
produce new individuals
– specific adaptations
include stolons, rhizomes,
and tubers
22.1 Plant Life Cycles
Humans can produce plants with desirable traits using
vegetative structures.
• Vegetative propagation takes advantage of plants’ ability to
reproduce asexually.
• Humans use one plant with desirable traits to produce
many individuals.
– cutting of leaves or stems may grow new roots
– grafting joins the parts of
two plants together to form
a hybrid plant
22.1 Plant Life Cycles
KEY CONCEPT
Plant hormones guide plant growth and development.
22.1 Plant Life Cycles
Plant hormones regulate plant functions.
• Hormones are chemical messengers.
– produced in one part of an organism
– stimulates or suppresses activity in another part
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• Gibberellins are plant hormones that produce dramatic
increases in size.
– ending seed dormancy
– rapid growth of young
seedlings
– rapid growth of some
flower stalks
22.1 Plant Life Cycles
• Ethylene causes the ripening of fruits.
– some fruits picked before
they are ripe
– sprayed with ethylene to
ripen when reach
destination
22.1 Plant Life Cycles
• Cytokinins stimulate cytokinesis.
– final stage in cell division
– produced in growing roots, seeds, and fruits
– involved in growth of side branches
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• Auxins lengthen plant cells in the growing tip.
– stimulates growth of
primary stem
– controls some forms of
tropism
• A tropism is the movement
of plant in response to an
environmental stimulus.
22.1 Plant Life Cycles
Plants can respond to light, touch, gravity, and seasonal
changes.
• Phototropism is the
tendency of a plant to
grow toward light.
– auxins build up on
shaded side of stem
– cells on shaded
side lengthen
– causes stem to
bend toward light
22.1 Plant Life Cycles
• Thigmotropism is a plant’s response to touchlike stimuli.
– climbing plants and vines
– plants that grow in direction of constant wind
22.1 Plant Life Cycles
• Gravitropism is a plant’s response to Earth’s gravitational
pull.
– positive gravitropism is downward growth (roots)
– negative gravitropism is upward growth (shoots)
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• Some plants have rapid responses not involving growth.
– Some responses protect
plants from predators.
– Some responses allow
plants to capture food.
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• Photoperiodism is a response to the changing lengths of
day and night.
– triggers some plants to flower
– triggers fall colors/winter dormancy of deciduous trees