Final answer:
The placenta is the pregnancy organ that deposits the most protein, playing a critical role in nutrient and waste exchange between the mother and the fetus.
Step-by-step explanation:
The organ that deposits the most protein during pregnancy is the placenta. The placenta serves a vital role in supporting the developing fetus by facilitating nutrient and waste exchange between the mother and the fetus. This exchange includes proteins which are crucial for fetal growth and development. As the fetus grows, the nutrient and gas exchange requirements increase, and the placenta, which is a unique circulatory organ formed jointly from the embryo and uterine wall structures, adapts to meet these demands.
The umbilical vein carries nutrient-rich and oxygen-rich blood from the mother to the fetus, and the two umbilical arteries return deoxygenated blood and waste from the fetus to the placenta. The placenta manages to perform these functions effectively by depositing proteins and other essential nutrients into the fetal circulation while also removing waste products.