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