Final answer:
The placenta is the organ responsible for the exchange of nutrients, gases, and waste between the mother and fetus, connected to the fetus via the umbilical cord. The umbilical vein carries oxygen-rich blood to the fetus, while the umbilical arteries remove waste.b. placenta.
Step-by-step explanation:
The organ that allows the exchange of nutrients, gases, and waste between the mother and the fetus is called the placenta. The placenta is a temporary but critical organ that develops in the uterus during pregnancy. It forms a connection between the mother's and the fetus's blood circulation systems without mixing their blood. This connection is facilitated by a structure called the umbilical cord, which contains two arteries and a vein.
The umbilical vein carries oxygen-rich blood and nutrients from the mother to the fetus, while the umbilical arteries carry oxygen-depleted blood and waste products from the fetus back to the placenta. Here, the exchange of gases and other substances occurs, allowing the fetus to receive the necessary oxygen and nutrients for growth and development and to expel carbon dioxide and other waste products.
Therefore, the correct answer to the student's question is 'b. placenta.'