Plant Reproduction in seed bearing plants

The seed bearing plants or angiopsperms possess a male reproductive organ and female reproductive organ. The male reproductive organ is collectively termed as androecium and the female reproductive organ is collectively termed as gynoecium. The androecium consists of stamens which constitute anthers and filaments. Gynoecium consists of stigma, style and ovary. The ovary is also called as pistil or carpel. A flower might have a single pistil or many pistils. The anther produces several pollen grains which pollinate the female reproductive structures. The pollen reaches the stigma or receptive structure of the gynoecium through several modes such as wind, water, birds etc. The pollen that gets stuck on the stigma will undergo nuclear divisions to form two small cells. These two cells are generative cell and vegetative cell. The generative cell will give rise to two sperm nuclei while the vegetative cell will help in the pollen tube formation. The pollen tube takes the sperm nuclei towards the ovary and into the ovule through the style. The two sperm nuclei enter the ovule through the micropylar end. The ovule is the female gametophyte which has an egg nucleus flanked by two synergid cells. The egg is situated at the micropylar end of the ovule. The center of the ovule consists of two polar nuclei. The other end of the ovule consists of three antipodal cells. The sperm nuclei penetrate into one of the synergids to enter into the ovule and unite with the egg nucleus. The other sperm nucleus will form a triploid primary endosperm nucleus with the two polar nuclei at the center. The union of egg and sperm give rise to a zygote while the endosperm nucleus gives rise to endosperm tissue after several divisions. The zyote develops into embryo. The ovule forms embryo inside it and it transforms into a seed. The outer part of the ovule and the ovary wall form the rest of the part of the fruit. The ovary becomes a fruit while the ovules get converted to seeds. These seeds will keep the embryo viable for germinating into a new plant.