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biology 0610printed 214 · PDF 214
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printed 214 · PDF 214
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end of the oviduct. This is called ovulation.
● Sperm after being made by the testes are stored in the epididymis.
● Sperm production is very heat sensitive. This is why testes are found outside
the body where they are cooler than they would be inside.
● Eggs and sperms are both haploid cells and are made by meiosis.
● The egg cell has a jelly coat surrounding it.
● The sperm has an acrosome in its head. It is a vesicle containing enzymes
to dissolve a way through the jelly surrounding the egg cell.
● It also has a flagellum or tail to help it swim and move.
Fertilisation
● After ovulation the egg is caught in the funnel of the oviduct. Very slowly the
the egg travels towards the uterus. Cilia lining the oviduct help it move around.
Muscles in the walls also help it move by producing gentle rippling
movements.
● If a sperm does not fertilise the egg within 8 to 24 hours the egg cell dies.
● For sperm to reach the egg easily the penis is placed inside the vagina.
● Then the sperm is squeezed out of the penis due to rhythmic contractions.
● The semen containing the sperm is deposited at the top of the vagina near the
cervix. The sperms still have a long way to go.
● To help them swim they use their flagella and the energy from the
mitochondria inside them. They move through the cervix, through the uterus
and into the oviduct.
● When a sperm cell comes into contact with the jelly coat surrounding the egg
the cell its acrosome becomes activated. It releases enzymes and they digest the
jelly coat.
● This allows for the head of the sperm to move inside and get into the
cytoplasm of the cell. The nucleus in the sperm then fuses with the nucleus of
the egg. This is fertilisation.
● As soon as the successful sperm enters the egg cell, its jelly coat becomes
impenetrable and all other sperm are left outside to die.