Final answer:
The best diagram would show a blastocyst, which is characteristic of the 64-cell stage embryo, consisting of a blastocoel, an inner cell mass, and a surrounding trophoblast layer.
Step-by-step explanation:
The diagram that best represents the nucleus of an embryo at the 64-cell stage grown from a single cell would illustrate the blastocyst stage of the embryonic development. This stage occurs after the morula phase and before implantation in the uterine wall. The blastocyst consists of a fluid-filled cavity known as the blastocoel, with an inner cell mass surrounded by a layer of cells called the trophoblast. These structures are crucial in the embryo development, leading to the formation of the embryo's body and the supportive structures like the placenta.
The embryonic stage is characterized by rapid development where foundational tissues and organs start to form. By the end of the embryonic stage, distinct human features become more apparent, and the beginnings of limbs and facial structures can be observed in the growing embryo.