To ensure effectiveness of reproduction in mammals, which of the following happens?
The correct option is D Formation of placenta
The placenta is a temporary endocrine organ formed during pregnancy, which produces hormones important in the maintenance of pregnancy in mammals. Placenta allows the exchange of nutrients and gasses between the mother and the developing fetus through blood. Antibodies also pass from the mother to the fetus to provide protection from diseases. Also, it acts as a barrier between mother and the fetus, preventing some harmful substances in the blood of the mother from damaging the fetus. So, if the placenta is missing, then the fetus will not be able to get nutrition and there will be mixing of blood from mother to fetus, which could be harmful to the fetus.
Thus, the correct answer is option D.