Concept:The structure labelled I is the organ of exchange between the mother and the developing foetus in a mammalian pregnancy.
Explanation:The diagram shows a developing foetus enclosed in the uterus.
The organ labelled I is the placenta, which is attached to the inner wall of the uterus.
It is joined to the foetus by the umbilical cord.
Through the placenta, oxygen and dissolved nutrients diffuse from the mother's blood into the foetus's blood.
Carbon dioxide and other excretory wastes move from the foetus into the mother's blood for removal.
The oviduct is the tube that carries eggs from the ovary to the uterus, not the labelled organ.
The amnion is the membrane that forms a fluid-filled sac around the foetus, not a disc attached to the uterine wall.
The uterus is the muscular chamber housing the foetus, but the placenta is the specific structure indicated at label I.
Answer:B. placenta
