Final answer:
The placenta allows for the exchange of substances between the mother and fetus, including waste products. Statement 3 is correct, as waste products diffuse out of the placenta into the maternal blood. The placenta also secretes human chorionic gonadotropins (hCG) to support pregnancy.
Step-by-step explanation:
The placenta is a fully developed organ that provides nutrition and excretion, respiration, and endocrine function. It allows for the exchange of gases, nutrients, and other substances between the mother and the fetus without mixing their blood. Waste products, such as carbon dioxide, pass from the fetal bloodstream into the maternal blood for elimination.
Regarding the statements given, statement 3 is correct: waste products diffuse out of the placenta into the maternal blood. Statement 1 is incorrect because the placenta is not permeable to all bacteria. Statement 2 is incorrect because oxygen and carbon dioxide can freely diffuse through the placenta.
The placenta also secretes human chorionic gonadotropins (hCG), which are hormones that support pregnancy and are detected in pregnancy tests.