1. Sexual Reproduction in Plants Continued…

2. 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, self- pollination and cross-pollination.

3. 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 cross- pollination are wind and insects

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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