The life cycle alternates between a haploid gametophyte and a diploid sporotype, just like in all plants. The angiosperm has enclosed seeds and ovules in a leaf known as a carpel. The carpel protects the ovules and seeds and it also interacts with the incoming pollen too. This helps in preventing self-pollination so as to favor cross-pollination and to increase genetic diversity. You can get a diagram on the life cycle at http://en.wikipedia.org/wiki/File:Angiosperm_life_cycle_diagram.svg.