sexual reproduction

Reproductive organs in flowering plants. The stamens are the male parts of the plant. Each consists of a stalklike filament topped by an anther. The anther contains four pollen sacs which burst to release tiny grains of pollen, the male sex cells. The carpels are the female reproductive parts. Each carpel has a stigma which catches the pollen grain. The style connects the stigma to the ovary. The ovary contains one or more ovules, the female sex cells.

The human reproductive organs. In the female, gametes called ova are released regularly in the ovaries after puberty. The Fallopian tubes carry the ova to the uterus or womb, in which the fetus will develop. In the male, sperm is produced inside the testes after puberty; about 10 million sperm cells are produced each day, enough to populate the world in six months. The sperm duct or vas deferens, a continuation of the epididymis, carries sperm to the urethra during ejaculation.

The anatomy of the human sexual organs, front and side views.

Reproductive process in organisms that requires the union, or fertilization, of gametes (such as eggs and sperm). These are usually produced by two different individuals, although self-fertilization occurs in a few hermaphrodites such as tapeworms. Most organisms other than bacteria and cyanobacteria show some sort of sexual process. Except in some lower organisms, the gametes are of two distinct types called the egg (ovum) and the sperm. The organisms producing the eggs are called females, and those producing the sperm, males. The fusion of a male and female gamete produces a zygote, from which a new individual develops. See reproduction.

Gametes are produced by meiosis. If the male and female gametes are produced by two different individuals, sexual reproduction combines inherited information from the two parents. In mammals, the male gametes, sperm, are made in the testes, while the female gametes, eggs (ova), are made in the ovaries.

Most animals and plants reproduce sexually, though quite a few plants also reproduce asexually. The male and female sex organs of a plant are usually found in a flower. Many flowers contain both male and female organs. The male gametes of a plant are inside the pollen grains, and the female gametes are inside the ovules.

In micro-organisms, asexual reproduction is very common. Yeasts and a few bacteria may reproduce sexually, although most reproduce asexually.

The alternatives to sexual reproduction are binary fission, budding, vegetative reproduction, parthenogenesis, and spore formation.

Other forms of reproduction The alternatives to sexual reproduction are parthenogenesis and asexual reproduction by means of spores.