In flowering plants, the flower is the unit of sexual reproduction; it involves pollination, double fertilization and formation of seed and fruit.
- Flower: it has four whorls: calyx, corolla, androecium (male, made of stamens) and gynoecium (female, made of carpels). Each carpel has an ovary with ovules, a style and a stigma. Inside each ovule an embryo sac with a haploid egg cell and two polar nuclei is formed by meiosis. Pollen grains are formed by meiosis in the anthers.
- Pollination: transfer of pollen grains from anther to stigma by wind, water, insects or other animals. It may be self-pollination (same flower or same plant) or cross-pollination (two plants of the same species).
- Double fertilization: on the sticky stigma the pollen grain germinates and forms a pollen tube carrying two male gametes. The tube reaches the embryo sac through the style. One male gamete fuses with the egg cell to form the zygote; the other fuses with the two polar nuclei to form the endosperm.
- Seed and fruit: after fertilization the ovule develops into a seed and the ovary into a fruit. The seed germinates in soil and the embryo grows into a new plant using the food stored in the endosperm.