Role of the Placenta (Edexcel IGCSE Biology)
Revision Note
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The Placenta
After fertilisation in the oviduct the zygote divides to form an embryo, and travels to the uterus
Upon reaching the uterus the embryo implants in the uterine lining, where it continues to develop
A structure called the placenta forms at the implantation site
In the placenta the mother’s blood comes into very close proximity to the blood of the fetus
The umbilical cord connects the embryo’s blood supply to the placenta
The role of the placenta is to enable exchange of substances between the mother's blood and that of the fetus
Substances that travel from the mother's blood to the fetus include:
oxygen
nutrients, e.g. glucose, amino acids and mineral ions
Substances that travel from the fetus' blood to the mother include:
carbon dioxide
urea
The placenta is an efficient exchange surface because it has:
a large surface area
a thin wall for efficient diffusion
The placenta also acts as a barrier to toxins and pathogens, although not all are stopped from passing through, for example:
nicotine and alcohol can pass across the placenta
virus particles can pass across the barrier
The placenta allows exchange of substances between the fetus and the mother
Examiner Tips and Tricks
It is worth learning at least two examples of substances that move in either direction across the placenta – this is a common exam question and non-specific answers such as ‘waste products’ and ‘nutrients’ will not get any marks!
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