Which statement about placental mammals is true?
A) A moderate amount of yolk supports the embryo prior to implantation.
B) As the blastocyst reaches the uterus, it hatches from the trophoblast.
C) The blastocyst produces the body of the embryo, and the maternal tissues produce the entire placenta.
D) The zona pellucida promotes early implantation.
E) Chorionic villi develop from the trophoblast and increase the embryo's area of contact with the maternal circulatory system.

Question

Quizplus · Accepted Answer

Chorionic villi develop from the trophoblast and increase the embryo's area of contact with the maternal circulatory system. This allows for exchange of nutrients, gases, and waste products between the maternal and fetal bloodstreams, which supports the growth and development of the fetus. The other statements are all incorrect. A moderate amount of yolk is found in the eggs of monotremes and marsupials, but not in placental mammals, which obtain nutrients from the maternal blood supply via the placenta. The blastocyst does not hatch from the trophoblast, but rather attaches to and implants in the uterine wall. The body of the embryo and the placenta are both formed from both embryonic and maternal tissues, with the trophoblast contributing to the placenta. The zona pellucida surrounds the egg and helps to prevent polyspermy, but it does not promote implantation.

Which Statement About Placental Mammals Is True