Which organ connects the embryo to the uterine wall and provides essential nutrients?

The placenta serves as the critical organ that connects the embryo to the uterine wall, facilitating a vital relationship between the mother and the developing fetus. It is responsible for the exchange of nutrients, gases, and wastes, ensuring that the embryo receives the essential substances required for growth and development. The placenta also plays a role in hormonal regulation during pregnancy and acts as a barrier to harmful substances.

In contrast, while the amnion provides a protective fluid-filled sac around the embryo, it does not directly supply nutrients or connect to the uterine wall. The chorion is involved in forming part of the placenta and is crucial for gas exchange, but its primary function is not the direct provision of nutrients. The embryo sac, referring to the structure that contains the embryo and supporting materials in plants or certain animals, does not relate to nutrient transfer in the context of mammalian pregnancy. Therefore, the placenta is indeed the essential organ described in the question.