• Humans reproduce sexually. Fertilisation is internal.
• The sperm are produced in the tests by meiosis. During sexual intercourse, they pass
along the sperm duct and are mixed with a fluid. This forms semen which is ejaculated
into the vagina.
• One ovum is released into a Fallopian tube each month from an ovary. If an ovum is
present in the Fallopian tube, then it may be fertilised by sperm which enters the vagina
during sexual intercourse.
• Once the sperm has reached the ovum, its nucleus must enter the ovum and fuse with
the ovum nucleus. As each gamete is haploid, the zygote formed in fertilisation will be
diploid.
• Fertilisation also provides an additional source of genetic variation. The sperm and ova
are all genetically different because they are formed by meiosis. Therefore each time
fertilisation take place, it brings together a different combination of genes.
• The zygote formed then begins to develop into an embryo which will implant in the
lining of the uterus.
• Here, the embryo will develop a placenta, which will allow the embryo to obtain
materials such as oxygen and nutrients from the mother’s blood. It also allows the
embryo to get rid of waste products. And it anchors the embryo in the uterus.
• During pregnancy, a membrane called the amnion encloses the developing uterus. The
amnion secrets a fluid called amniotic fluid which protects the embryo against jolts and
bumps.
• When the embryo becomes recognisably human, it becomes called a foetus.
Human reproductive systems:
Male:
• Makes sperm in the testes (all the time after puberty).
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