Semen or seminal fluid is the whitish viscous fluid emitted from the male reproductive tract that contains sperm & liquids (seminal plasma) that help keep them viable. Sperm cells, produced by the testes in humans, represent 2 to 5 percent of semen volume; fluids from tubules, glands, & storage areas of the reproductive system bathe them as they travel down, nourishing them, keeping them motile, or participating in certain chemical reactions. During ejaculation, liquids from the prostate gland & seminal vesicles dilute the sperm & provide a suitable, slightly alkaline environment. An average ejaculation of a human male expels 0.1 to 0.3 cubic inches (2 to 5 ml.), containing 200 to 300 million sperm.
Sperm is the smaller, usually motile male reproductive cell of most organisms that reproduce sexually. Sperm cells are haploid (they have 1/2 the No. of chromosomes as the other cells in the organism's body). Sperm often have at least 1 flagellum. During fertilization, the nucleus of a sperm fuses with the nucleus of the much larger oocyte (the female reproductive cell) to form a new organism. In male animals, sperm are normally produced by the testes in extremely large numbers in order to increase the chances of fertilizing an egg. Motile sperm cells produced by some multicellular protist groups (such as the algae), the bryophyte plants, & the seedless vascular plants, require water to swim to the oocyte. In gymnosperms and angiosperms, sperm do not need water for mobility but are carried to the female reproductive organs in the pollen grain. In the cycads and the gingko (both gymnosperms), the sperm are motile & propel themselves down the pollen tube to reach the egg cell. In the conifers and angiosperms, the sperm are not themselves motile but are conveyed to the ovule by the growing pollen tube.
The human sperm cell is divided into a head that contains the nucleus, a mid-piece that contains mitochondria to provide energy for the sperm, & a flagellum that allows the sperm to move. When fertilization occurs, the nucleus & other contents from the sperm cells are drawn into the cytoplasm of the oocyte, but the mitochondria in the sperm are destroyed & do not survive in the zygote. Since mitochondria contain their own DNA (thought to be a relic from an existence as separate symbiotic organisms), all of the mitochrondrial DNA in humans is thus inherited from the female. The semen produced by the male reproductive tract act as a medium for sperm typically contains over 100 million sperm cells, all of which have but one purpose: to fertilize the single available oocyte.
Nothing semen covers the sperm so that they make it into the vagina safely and it also helps it keep the sperm safe so if any thing happens inside the penis or something the semen is wiped away and not the penis