Everything about Sperm totally explained
The term
sperm is derived from the Greek word (σπέρμος)
spermos (meaning "seed") and refers to the male reproductive cells.
Sperm cells are the smaller
gametes involved in
fertilization in
anisogamy and
oogamy. In these types of
sexual reproduction, there's a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. A uniflagellar sperm cell that's
motile is also referred to as
spermatozoon, whereas a non-motile sperm cell is referred to as
spermatium. Sperm cells can't divide and have a limited life span, but they can fuse with
egg cells during fertilization to form a
totipotent zygote with the potential to develop into a new organism. Mammalian sperm cells can live for up to 3 days inside the female unless it's exposed to air or is mixed with another liquid.
The spermatozoa of animals are produced through
spermatogenesis inside the male
gonads (
testicles) through
meiosis. Sperm cells in algal and many plant
gametophytes are produced in male
gametangia (
antheridia) through
mitosis. In
flowering plants, sperm nuclei are produced inside
pollen.
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're multi-flagellated (carrying more than one flagellum).
Non-motile sperm cells
Non-motile sperm cells called
spermatia lack flagella and therefore can't swim. Spermatia are produced in a
spermatangium.
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.
Sperm nuclei
In many
land plants, including most gymnosperms and all
angiosperms, the male
gametophytes (
pollen grains) 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 for fertilization. More than 50 countries worldwide are importers, including Paraguay, the US, Kenya and Hong Kong.
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