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Semen
 pH 7.2 – 7.8
 Volume per ejaculate: 2—6 ml
 Number of sperm: 50—130 million
If sperm make up only 5% of semen, what is the rest for?
The journey of a sperm from the testis to the ovum is long and hazardous, and the
semen contains components that will aid the sperm on its way.
Some of the hazards sperm will encounter are:

Acids. The pH of the vagina is 3.8—4.5

Distance. The distance from the vagina to the oviduct is about 20cm long

Location. Sperm has to travel from the vagina up through the cervix and
uterus to reach the oviducts where fertilisation takes place
The table below shows some of the constituents of semen and the glands that
produce them. Complete the table by filling in the likely function of each.
COMPONENT
WHERE
PRODUCED?
Sperm
Testes
Mucus (alkaline)
Seminal vesicles,
Cowper’s glands
Fructose (a sugar, amino
acids, vitamin C,
galactose (a sugar)
Seminal vesicles,
prostate,
Cowper’s glands
Coagulating agent
Seminal vesicles
Causes semen to thicken during the early
stages after ejaculation
Anti-coagulating agent
Prostate gland
Later on, these chemicals cause the semen
to become more liquid
Prostaglandins
Seminal vesicles
Suppresses female immune system
4th form | Semen & fertilisation | 2010
FUNCTION(S)
Fertilisation
When the sperm has arrived at the ovum its job is almost done. All that remains is
for the sperm’s nucleus, contained in the head part of the sperm, to fuse with the
ovum nucleus. This occurs in the oviduct (not the uterus!).
To gain entry to the ovum the sperm must:
a) Burrow through the loose outer layer of cells of the ovum (called
the corona radiata).
b) Release chemicals that digest the next layer of the ovum (the zona
pellucida).
c) Penetrate the cell membrane and enter the cytoplasm.

How does the sperm penetrate the zona pellucida to reach the cytoplasm?
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After entry of the sperm the zona pellucida thickens and becomes impenetrable to
other sperm.

Why is it important that other sperm are excluded from the ovum?
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Once inside the ovum the tail is lost and the head, containing the nucleus, becomes
the male gamete. The nuclear membranes disappear so that the two nuclei can fuse.
This is fertilisation.
The cell is now referred to as a zygote.

How many sets of chromosomes will a cell of a human zygote have?
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Following fertilisation the zygote will begin a series of cell divisions and moves down
the oviduct towards the uterus where it implants in the uterine lining.
4th form | Semen & fertilisation | 2010
4th form | Semen & fertilisation | 2010