Sexual Reproduction in Plants

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