Concept:The foetus exchanges substances with the mother through the placenta, but the foetal blood and maternal blood never mix directly.
Explanation:The placenta has a thin membrane that separates the mother's blood from the foetus's blood.
Food and oxygen diffuse from the mother's blood into the foetus's blood across this membrane.
Carbon dioxide and other waste products diffuse in the opposite direction, from the foetus to the mother.
This shows that the foetus depends on the mother's blood for food and oxygen, so option B is correct.
The foetus is also enclosed in a fluid-filled water sac, which protects it, so option C is correct.
Nutrients and oxygen are indeed carried across the placenta to the embryo's blood, so option D is correct.
However, because of the placental membrane, the foetal circulatory system is not directly connected to the maternal blood vessels.
Therefore, option A contains the incorrect statement.
Answer:A. The circulatory system of the foetus is directly connected to the maternal blood vessels