Final answer:
The placenta in mammals is a spongy structure that connects the developing fetus to the mother, facilitating the transfer of oxygen, nutrients, and wastes. It supports prenatal development by nourishing and protecting the fetus and contributes to the success of placental mammals by allowing the birth of large, mature infants.
Step-by-step explanation:
The placenta performs critical functions during mammalian pregnancy. It forms after fertilization and serves as a temporary organ that connects the developing fetus to the mother. The placenta facilitates the exchange of nutrients, oxygen, and wastes between the maternal and fetal bloodstreams. It acts not only as a transportation medium for nutritional substances and gaseous exchange but also plays roles in excretion, respiration, and endocrine functions.
In placental mammals, which include the majority of mammals, the placenta allows a fetus to grow significantly within the mother's uterus, due to its ability to provide nourishment and protection against the mother's immune system. This extended prenatal development results in the birth of relatively large and mature infants compared to other mammalian groups, contributing to the success of placental mammals. The placenta also moves carbon dioxide and other metabolic wastes from the fetus back to the mother for excretion, thereby maintaining the fetus's homeostasis.