Humans, along with all other mammals, reproduce by sexual reproduction.
This means that an egg (from the mother) needs to be fertilized (that means join up with)a single sperm (from the father).
Fertilization is internal which means that the egg is fertilized inside the mothers body and not outside (as with a fish, for example).
The sperm are made in the testis. They leave the man’s body through his penis. They are much smaller than the egg and can move by thrashing their tail.
The eggs are made in the ovary and one egg is released every 28 days.
Actual size of egg = ·
The sperm enter the mothers body through the birth canal .
The egg is fertilized in the Fallopian tube.
After fertilization the egg cell starts to divide and an embryo begins to form. The embryo develops in the womb (uterus)
Development of the embryo
The embryo obtains food through its umbilical cord which is attached to the mother at the placenta.
The umbilical cord, placenta, heart and brain are the first organs to form.
When the embryo is recognisable as a baby (after about 2 months of development) it is known as a fetus.
After about 4 months the embryo is nearly completely developed, but is still small (about 15cm).
In about another 5 months the baby is ready to be born and the body will have turned so that the head faces downwards towards the vagina (birth canal)
The total time from fertilization (conception) to birth is known as the gestation period which in humans is
A new born baby weighs about 4kg. It’s head is quit large because the brain needs to be quite well developed.
At the age of about 13 a boy reaches puberty. This is when his sexual organs become mature and his body is able to produce sperm. Girls reach puberty slightly younger than boys.
The placenta is an organ which attaches the embryo to the mother via the umbilical cord.Food and oxygen pass from the mother’s blood to that of the embryo.Waste passes back from the embryo to the mother.
Other dangerous chemicals, such as alcohol or medicines, can also pass from the mother to the embryo and effect its growth.
Note that the mother’s blood cells do NOT pass across the placenta. If they did it could seriously harm the baby and the mother.
WORDS TO KNOW
KIDNEY i) Removes waste from the blood.
ii) Removes water from the blood and so controls the blood concentration. The urea + water form urine. The urine passes down the URETER to the bladder.
BLADDER Stores urine.
TESTIS Where sperms (male gamete) are manufactured.
PENIS Where urine and sperm leave the body.
OVARY Where eggs/ova (female gamete) are manufactured.
FALLOPIAN TUBE Carries the eggs from the ovary to the womb (uterus).
(egg duct) Where an egg is fertilized. The eggs take about seven days to travel down the Fallopian tube.
UTERUS Organ where the embryo develops.
EMBRYO The young child inside the uterus. While the child is only partly formed it is often called a FETUS.
AMNION A water filled sac that helps support and protect the developing embryo.
PLACENTA An organ that supplies the developing baby with food and oxygen from the mother’s blood. Waste travels back through the placenta from the embryo to the mother. Other substances (alcohol, nicotine, drugs) can also travel through the placenta and these can effect the development of the unborn baby.
Blood cells do NOT pass through the placenta.
UMBILICAL CORD A tube that joins the unborn baby to the mother
FERTILIZATION The joining of an egg and a sperm.
GESTATION PERIOD The time taken for the unborn baby to develop inside the mother (ie the time from fertilization to birth)
In a human this is 9 months.