Final answer:
The placenta is a vital temporary organ that facilitates the exchange of nutrients and wastes between the mother and the developing embryo or fetus without the blood of the mother and fetus mixing.
Step-by-step explanation:
The placenta is a pancake-shaped mass of tissue that permits the embryo and fetus to exchange nutrients and waste with the mother. This temporary organ consists of a large mass of blood vessels from both the mother and the developing embryo or fetus, allowing for a critical exchange of substances. The mother's and embryo's or fetus's blood exchange nutrients, oxygen, antibodies, hormones, and other necessary substances across the placental barrier, while waste products such as urea and carbon dioxide are passed from the offspring to the mother for excretion. The placenta protects the fetus from being attacked by the mother's immune system and is connected to the fetus via the umbilical cord.