The Angiosperm Life Cycle

Angiosperm flowers contain two key reproductive structures: stamens and carpels. Stamens produce male spores called microspores in their anthers, which develop into pollen grains. Carpels contain ovaries with ovules that produce female spores called megaspores, which develop into embryo sacs containing eggs. These structures enable sexual reproduction in flowering plants.

Double fertilization occurs when a pollen tube extends to the ovule and releases two sperm cells. One sperm fertilizes the egg to form a zygote that develops into an embryo. The second sperm fertilizes the central cell of the embryo sac, forming the endosperm—a nutrient storage structure. This unique process produces both an embryo and a nutrient supply within the developing seed.

Megaspores are female spores produced in the ovule's megasporangium through meiosis. Of the four megaspores produced, only one survives and develops into an embryo sac—the female gametophyte. The embryo sac contains the egg cell and other supporting cells necessary for fertilization and early seed development.

Microspores are produced in the anther through meiosis and develop into pollen grains, the male gametophyte. Each pollen grain contains two cells: a tube cell and a generative cell. When pollen reaches the stigma, the tube cell forms a pollen tube that grows toward the ovule, while the generative cell divides to produce two sperm cells for fertilization.

After fertilization, the ovary develops into fruit development structure and function, which typically contains multiple seeds or fertilized ovules. The fruit's form varies by species and may resemble the original ovary or incorporate additional tissues and structures. Fruits protect seeds and aid in their dispersal to new locations for plant reproduction.

A mature angiosperm seed contains three main components: a protective seed coat, an embryo (the young plant), and endosperm (nutrient storage tissue). The embryo and endosperm are packed together within the seed coat. When conditions are favorable, the seed germinates and develops into a mature sporophyte that produces flowers and begins another life cycle.

The angiosperm life cycle is dominated by the diploid sporophyte stage—the familiar flowering plant—rather than the haploid gametophyte stage. The sporophyte produces spores through meiosis in its reproductive organs, while the gametophyte stages (pollen and embryo sac) are small and dependent on the sporophyte. This dominance reflects the evolutionary success of angiosperms as the most diverse plant group on Earth.