Sexual Reproduction
in Plants
Continued…
Pollination in Angiosperms
 Before seeds can develop inside a
flower, pollen grain from the anthers must
reach the stigma of the pistil – this is
called pollination
 There are two types of pollination, selfpollination and cross-pollination.
Self-Pollination
 Both male and female gametes come from
the same plant
Cross-Pollination
 The pollen from one flower is transferred
to a flower on a different plant
 The two most common agents of crosspollination are wind and insects
How does pollination
occur??
 First a grain of pollen lands on the stigma
 Second, a pollen tube grows down the
style into the ovary and enters the ovule
 Third, a sperm is formed through meiosis
and travels down the tube to fertilize one
egg
 Forth, one sperm fertilizes one egg
Seed Development in
Angiosperms
 While the pollen tube is growing, cells inside
the ovule prepare for its arrival
 When the sperm reaches an egg, a zygote is
formed
 Other cells in the ovule develop into a
cotyledon – which contains stored food
 The zygote itself goes through mitotic division
to form a many-celled embryo with a miniature
leaf, root, and stem
 This cotyledon surronds the embryo and the
sac around the ovule develops into a seed coat
Seed Dispersal in
Angiosperms
 Dispersal is the transport of seeds away
from the parent plant
 Some fruits can launch their own seeds
while others need help from outside
agents
Sexual Reproduction in
Gymnosperms
 Remember that gymnosperms do not bear
flowers
 Most gymnosperms produce their seeds inside
cones – they are often called conifers
 In most familiar species the same tree
produces both types of cone
 Like an angiosperm, the seed of a
gymnosperm contains an embryo, a food
supply, and a coat that protects it from drying
out
Seed Development in
Gymnosperms
 The mature plant produces cones for sexual
reproduction
 Female cones produce ovules – an egg is
produced inside the ovule through meiosis
 Male cones produce pollen by meiosis
 A pollen grain carried by the wind lands directly
on an ovule and forms a pollen tube
Seed Development in
Gymnosperms Cont..
 A sperm travels down the pollen tube and
fertilizes an egg to form a zygote
 The zygote develops into an embryo and
a food supply is built up
 The female cone sheds a winged seed
that may germinate and grow into a
seedling, if conditions are favorable