Which of the following statements about the development of the foetus is not correct?

Analyze the question: We need the statement that is NOT correct about foetal development.

Concept: The foetus develops in the uterus and is connected to the mother through the placenta and umbilical cord. Key facts:

• The foetal and maternal blood circulations are separate. They come very close in the placenta, but the blood does not mix.
• Exchange happens by diffusion across thin placental membranes: oxygen, glucose, amino acids, and antibodies go to the foetus, while carbon dioxide and urea go to the mother.
• The foetus is surrounded by the amniotic sac, which contains amniotic fluid. This cushions it against shock and keeps it moist.

Checking each option:

• A. The circulatory system of the foetus is directly connected to the maternal blood vessels. This is false. There is no direct connection, because the blood vessels are separated by placental tissue, and the two bloods do not mix. This is partly why the mother and baby can have different blood groups.
• B. The foetus depends on the mother's blood for food and oxygen. This is true, since nutrients and oxygen come from the mother's blood via the placenta.
• C. The foetus is surrounded by a water sac. This is true. It is the amniotic sac with amniotic fluid.
• D. Food and oxygen are carried across the placenta to the embryo's blood. This is true, by diffusion across the placenta.

Answer: The incorrect statement is A.

Tip: When you see "directly connected" or "blood mixes" in a question about the placenta, be suspicious. The mother's and foetus's blood never mix. Substances only diffuse across the placenta.