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The developing embryo





After fertilisation, the newly-formed zygote divides repeatedly to form a ball of cells called an embryo.

This becomes implanted in the wall of the uterus.

After eight weeks of development, the embryo is called a fetus. [1]

The fetus is surronded by amniotic fluid.

Breast feeding

Amniotic sac

- membrane which encloses amniotic fluid, broken at birth. [2]

Amniotic fluid

- protects foetus against mechanical shock, drying out and temperature fluctuations [3]

Placenta and umbilical cord

A placenta, connected by an umbilical cord, develops from the embryo.

The placenta anchors the embryo in the uterus.

It also allows:

- nutrients and oxygen to move from the mother to the embryo

- waste materials and CO2 to move from the embryo to the mother

There is no physical connection between the circulatory systems of the embryo and its mother, so their blood doesn’t mix.

These materials pass from one to the other by diffusion. [4]



[2] From Znotes CIE IGCSE Biology - 16.10 Sexual Intercourse

[3] From Znotes CIE IGCSE Biology - 16.10 Sexual Intercourse


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