Flowers contain reproductive organs called stamens and carpels. Stamens contain pollen and carpels contain ovaries with egg cells. Flowers can be unisexual with only stamens or carpels, or bisexual with both. Pollination is the transfer of pollen from stamen to carpel, allowing the male gamete in pollen to fuse with the female gamete in the ovule through a pollen tube. This fertilization produces a seed containing an embryo inside the ovary, which develops into a fruit.