Transcript Seed Reproduction

Pg. 109-119
The Importance of Pollen
and Seeds
• Oak, maple, and other shade trees are seed plants.
• All flowers are produced by seed plants. In fact, most
of the plants on Earth are seed plants.
• How do you think they became such a successful
group? Reproduction that involves pollen and seeds is
part of the answer.
Pollen
• In seed plants, some spores
develop into small structures
called pollen grains.
• A pollen grain is a small
structure produced by the
male reproductive organs
of a seed plant.
Pollen
• The sperm of seed plants are carried as part of the
pollen grain by gravity, wind, water currents, or
animals.
• The transfer of pollen grains to the female part of
the plant is called pollination.
• After the pollen grain reaches the female part of a
plant, sperm and a pollen tube are produced.
• The sperm moves through the pollen tube, then
fertilization can occur.
Seeds
• A seed consists of an
embryo, stored food,
and a protective seed
coat.
• The embryo has
structures that
eventually will produce
the plant’s stem, leaves,
and roots.
Seeds
• The stored food provides energy that is needed
when the plant embryo begins to grow into a plant.
• A new plant can develop more rapidly from a
seed than from a spore.
• The seed coat protects the seed from drying out.
Gymnosperm Reproduction
• Cones are the reproductive
structures of gymnosperms.
• Each gymnosperm species has
a different cone.
• The pine is a familiar
gymnosperm.
Cones
• A mature female cone consists of a spiral of
woody scales on a short stem. At the base of each
scale are two ovules.
• A female cone has 2 ovules where the eggs are
produced.
• Pollen grains are produced in the smaller male
cones.
Gymnosperm Seeds
• Pollen is carried from male cones to female cones
by the wind.
• To be useful, the pollen has to be blown
between the scales of a female cone.
• If the pollen grain and the female cone are the
same species, fertilization and the formation of a
seed can take place.
Angiosperm Reproduction
• All angiosperms have flowers.
• Most flowers have four main parts—petals, sepals,
stamen, and pistil.
Flower Parts and Functions
 Stamen – male




reproductive part of a
flower
Anther – where the
pollen is produced
Filament – supports the
anther
Petal – attracts insects
Sepal – protects the
flower bud
 Pistil – female
reproductive part of the
flower
 Stigma – sticky top part
that captures the pollen
 Style – pollen travels
down this tube to the
ovary
 Ovary – where eggs
(ovules) are located
Importance of Flowers
• The appearance of a plant’s
flowers can tell you
something about the life of
the plant.
• Large flowers with brightly
colored petals often attract
insects and other animals.
Importance of Flowers
• As they move about the flower, the animals get
pollen on their wings, legs, or other body parts.
• Later, these
animals spread
the flower’s pollen
to other plants
that they visit.
Importance of Flowers
• Other flowers depend on wind, rain, or gravity to
spread their pollen.
• Their petals can be small or absent.
Seed Dispersal
• Plants have many ways of dispersing their seeds.
• Most seeds grow only when they are placed on or
in soil.
• They fall onto the soil from the parent plant on
which they grew.
Seed Dispersal
• In nature some seeds can be spread great
distances from the parent plant.
• Wind dispersal
usually occurs
because a seed
has an attached
structure that
moves it with air
currents.
Seed Dispersal
• Animals can disperse many seeds.
• Some seeds are eaten with fruits, pass through an
animal’s digestive system, and are dispersed as the
animal moves from place to place.
• Attaching to fur, feathers, and clothing is another way
that seeds are dispersed by animals.
Seed Dispersal
• Water also disperses seeds.
• Raindrops can knock seeds out of a dry fruit.
• Some fruits and seeds float on flowing water or
ocean currents.
Germination
• Germination occurs when the
seed coat swells (because it
received water) and breaks
open and a plant grows from
a seed.
• Seeds will not germinate until
environmental conditions are
right.
• Temperature, the presence or
absence of light, availability of
water, and amount of oxygen
present can affect germination.