Transcript Gymnosperms P.P.

GYMNOSPERMS
REPRODUCTION AND LIFE
CYCLE
THE NAKED SEEDS
SPERMOPHYTA
(Gymno & Angio)
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seed plants
Vascular tissue
Use seeds for reproduction
Cell walls with cellulose
Don’t require water for reproduction
Dominant sporophyte
Microscopic gametophyte
BODY PLAN – Gymno only!
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Dominant diploid sporophyte
Have roots, stems, leaves, vascular tissue
Leaves = large or needle like
Have two types of cones
– Produce spores  gametophyte
• Gametophyte depends on sporophyte for nutrition
• Gametophyte = naked seed produced on outside of
cone
ADVANTAGES
• Transfer of pollen grains and development of
pollen tube eliminates the need for water for
sexual reproduction
• Gametophyte is very reduced and does not
develop in the soil as an independent generation,
instead the tiny gametophyte is contained and
protected within the moist reproductive tissue of
the sporophyte
• Evolution of the seed = protection of the dormant
embryo from drying out, cold …and is used to
disperse the seed to new habitats
DIVERSITY
CYCADS
• Grow in tropical and subtropical regions
• Look like palms except they have naked
seeds produced by big cones
• Abundant 300 million years ago
– were the food of herbivorous dinosaurs and the
fate of both of these groups of organisms was
probably closely linked.
DIVERSITY
GINKO
• This is a monotypic division, a single species of a
single genus, Ginkgo biloba the maidenhair tree..
Ginkgo biloba was preserved in the gardens of
Buddhist monasteries in China and Japan where it
was encountered by Westerners in the eighteenth
century. It has turned out to be a valuable street
tree because of its unusual foliage and tolerance of
pollution.
DIVERSITY
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CONIFER
Conifer leaves are needle or scale-like
often large and can dominate the plant
life in some ecosystems
their stems continue to expand in width
as well as length throughout the life of
the plant
The older parts of the stem become
woody, which provides a further
distinction from the seedless vascular
plants of which there are no surviving
woody representatives.
EX. Pine, Spruce, Cedar, Fir, Juniper…
THE CONIFER LIFE CYCLE
NAKED SEEDS  BIG TREES
The Dominant Sporophyte
• Diploid
• Produces male and female cones
BEGIN WITH DOMINANT
SPRORPHYTE = MATURE TREE
• The plant produces both male and female
cones
• MALE CONES ARE SMALL AND
PRODUCE POLLEN
GRAINS
FEMALE CONES ARE LARGE
The Male Cone
• Appears in the sring
• Cells in the cone divide by meiosis and
produce small haploid spores  pollen
grains
• Pollen Grain = immature male gametophyte
• Pollen grains are released into the air
Pollen grains
FEMALE CONES
• More familiar
• Larger spores form by meiosis = haploid
egg
• Female gametophyte stay inside tissue of
parent sporophyte
POLLINATION
• Pollen grain carried to female cone via wind
• When it arrives inside the female cone, each
pollen grain forms a tiny pollen tube
• Pollen Grain + Pollen Tube = Mature male
gametophyte
• Pollen tube grows into female gametophyte
until it reaches an egg
FERTILIZATION
• Occurs deep within the protective tissues of
the parent sporophyte
• A sperm nucleus from the pollen grain
unites with the egg  zygote
• In Pine it takes 15 months from pollination
to fertilization
DEVELOPMENT OF THE
EMBRYO
• Zygote cells undergo mitosis  embryo 
sporophyte plant
• Embryo surrounded by food storage tissue
(part of gametophyte)
• Protective coat of sporophyte tissue
develops around embryo and food
• By the time the food runs out, embryo has
chlorophyll and can make its own