The term sperm
is derived from the Greek word (σπέρμα) sperma
(meaning "seed") and refers to the male reproductive cells
. In the types of sexual reproduction
known as anisogamy
, there is a marked difference in the size of the gametes
with the smaller one being termed the "male" or sperm cell. The human
sperm cell is haploid
, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid
cell. A uniflagellar sperm cell that is motile
is referred to as a spermatozoon
, whereas a non-motile sperm cell is referred to as a spermatium
. Sperm cells cannot divide and have a limited life span, but after fusion with egg cells
during fertilization, a totipotent zygote
is formed with the potential to develop into a new organism. Mammalian sperm cells can live for up to 3 days inside the female reproductive system.
The spermatozoa of animals
are produced through spermatogenesis
inside the male gonads
) via meiotic
division. Sperm cells in algal and many plant gametophytes
are produced in male gametangia
) via mitotic
division. In flowering plants
, sperm nuclei are produced inside pollen
The sperm cell consists of a head, a midpiece and a tail. The head contains the nucleus
with densely coiled chromatin fibres, surrounded anteriorly by an acrosome
, which contains enzymes used for penetrating the female egg. The midpiece has a central filamentous core with many mitochondria spiralled around it, used for ATP
production for the journey through the female cervix
and uterine tubes
. The tail or "flagellum
" executes the lashing movements that propel the spermatocyte.
Motile sperm cells
Motile sperm cells typically move via flagella and require water in order to swim toward the egg for fertilization. The uniflagellated sperm cells (with one flagellum) produced in most animals are referred to as spermatozoa, and are known to vary in size.
Motile sperm are also produced by many protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes, they are multi-flagellated (carrying more than one flagellum).
In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.
In order to move towards the ova the sperm swim through the womans vaginal juices coating the walls of the womb and cervix.
Non-motile sperm cells
Non-motile sperm cells called spermatia
lack flagella and therefore cannot swim. Spermatia are produced in a spermatangium
Because spermatia cannot swim,they depend on their environment to carry them to the egg cell. Some red algae, such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.
Fungal spermatia (also called pycnidiospores) may be confused with conidia. Conidia are spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical with microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.
In many land plants
, including most gymnosperms and all angiosperms
, the male gametophytes
) are the primary mode of dispersal
, for example via wind or insect pollination
, eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma
of a receptive flower, it germinates and starts growing a pollen tube
through the carpel
. Before the tube reaches the ovule
, the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei which are then discharged through the tube into the ovule
In some protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.
A study by the University of California
has suggested that folate
may protect sperm cells from aneuploidy
On the global market, Denmark
has a well developed system of sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality
and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple. Furthermore, Nordic sperm donors tend to be tall and highly educated and have altruistic motives for their donations, partly due to the relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay
, and Hong Kong
. However, the Food and Drug Administration
(FDA) of the US has banned import of any sperm, motivated by a risk of mad cow disease
, although such a risk is insignificant, since artificial insemination is very different from the route of transmission of mad cow disease
. The prevalence of mad cow disease
is one in a million, probably less for donors. If prevalence was the case, the infectious proteins would then have to cross the blood-testis barrier
and the sperm would have to be swallowed orally to make transmission possible.