Transcript General Plant Life Cycle

Plant Life Cycles
Plant Evolution
• Descendants from green
algae (~450mya)
– Contain cellulose in cell
walls
– Contain chlorophyll
– Starch stored
• Land Plants Must Overcome
– Drying out
– Gas exchange
– Nutrient transport system
– Support
Land adaptations
• Cuticle: Waxy coating
prevents water loss
• Stomata: pores that
open/close to permit gas
exchange
• Roots & Stems: support
• Vascular system: tissue
that transports nutrients
– Nutrients & water go up
plant
– Sugars go down the
plant
General Plant Life Cycle
• Alternation of
generations
• Gametophyte
(haploid)
– Begins with spores
created by meiosis
– Mature
gametophyte
grows by mitosis
– Male & female
organs
– Sperm & egg
created
General Plant Life Cycle
• Sporophyte
(diploid)
– Begins when
sperm fertilizes
egg (zygote)
– Zygote divide by
mitosis to create
a mature
sporophyte
– Meiosis
produces
haploid cells
Mosses
• Nonvascular,
seedless
• Grow low to ground
to retain moisture
• Lack true leaves
– Leaf-like structures
only 1 cell thick
• Rhizoids anchor into
soil
• Early inhabitant of
new ecosystems
(succession)
• Gametophyte phase
– Dominant stage
– Carpet of moss
growing near ground
• Archegonium:
produces female egg
• Antheridium:
produces male
sperm
– Sperm swims through
water to fertilize egg
• Sporophyte phase
– Stalk grows up from
the gametophyte
– Sporangia houses
haploid spores
– Spores land and new
gametophyte grows
Moss Life Cycle
Ferns
• Seedless, vascular plants
– Vascular: allows taller growth
• Rhizoids: underground stems draw nutrients
• Fronds: leaves uncurl
– sporangia on underside
• Sori: sporangia
Fern Life Cycle
• Sporophyte phase
– Dominant stage
– Sporangia produces
haploid spores
– Spores released into air
• Gametophyte phase
– Spore grows into
prothallus
• Archegonium: produces
female egg
• Antheridium: produces male
sperm
– Sperm swims to egg
– Zygote begins sporophyte
stage
Conifers
• Seed advantages
– Don’t depend on
water
– Protects & nourishes
embryo
– Allow plants to grow in
new locations
• Conifers: woody cone
houses seeds
– Male cones: produce
pollen
– Female cones:
produce egg
• Pines, redwoods,
spruce, cedar
Conifer Life Cycle
• Sporophyte phase
– Cones grow on tree
– Female cones
• Megaspores inside
archegonia (gametophyte)
– Male cones
• Microspores (gametophyte)
released from antheridia
• sticks to archegonium
• Pollen tube grows from
pollen
• Sperm travels down pollen
tube (zygote/seed created)
• Sporophyte stage restarts
female
male
Flowers
• Reproductive
structure of flowering
plants
• Sepals
– outer ring of leaves
– protection
• Petals
– Inner ring of leaves
– Brightly colored to
attract pollinators
• Open petals & sepals
reveal male and
female structures
Flowers
• Female Carpal
– Inner most part
– Ovary: within the
base (female
gametophyte)
– Style: long stalk
– Stigma: sticky
tip, collects
pollen
• Male Stamen
– Surrounds carpal
– Filaments: long
stalks
– Anther: produces
pollen (male
gametophyte)
• 1) Flower matures and opens
• 2) Microscopes (male gametophytes) created in
the anthers
In the Anthers
• Meiosis makes 4 microspores
• In each microspore
– Nucleus splits in two
– 1 nucleus: forms pollen tube
– 1 nucleus: splits again to make 2 more nuclei
• 1 nucleus: fertilizes the egg
• 1 nucleus: fuses to make endosperm
• 3) Microspores continue to develop
• 4) Ovaries divide by meiosis to create
megaspore
In the Ovules
• Meiosis makes 4
megaspores (only 1
survives)
• In megaspore
– Mitosis creates 8 nuclei
– 1 nucleus: egg cell
– 2 nuclei: form embryo
sac
– 5 nuclei: disintegrate
Microspore lands on stigma
• 5 & 6) Pollen tube grows from pollen
– Two sperm nuclei follow down the pollen tube
• 7) Double fertilization:
– 1 sperm nuclei fuses w/ egg (zygote created)
– 1 sperm nuclei fuses w/ the embryo sac (endospore created)
• 8) Ovule hardens to form seed
Seed germinates
Fruit Production
• In the seed
– Embryo
– Endosperm
• Surrounding ovary grows into a
fruit
• Fruit attracts animals to eat and
spread the seeds
Fruit seeds in fox droppings
End of the Semester!