Final answer:
Among the substances listed, only alcohol can cross the placental barrier and reach the fetus. Other options like red blood cells, large proteins, and most bacteria do not typically pass through the placenta due to their size and the protective functions of the placental barrier.The right answer is A)
Step-by-step explanation:
The substances that can pass through the placenta to the fetus include lipid-soluble substances such as alcohol, but not red blood cells, large proteins, or most bacteria. While the placenta serves to exchange necessary nutrients and remove waste, it also acts as a barrier for most microorganisms. However, certain pathogens, including those grouped in the TORCH category, can cross the placental barrier.
Red blood cells and large proteins are generally too big to pass through the placental barrier. The structure of the placenta, including the chorionic villi, increases in surface area throughout gestation which facilitates the exchange of smaller molecules and substances, but it still does not allow the passage of red blood cells or large proteins into the fetal circulation.
Alcohol can readily pass through the placenta, which can lead to various developmental problems known as fetal alcohol spectrum disorders (FASD). This is why it is highly advised that pregnant individuals avoid alcohol consumption. Some bacteria, like those causing listeriosis, can also cross the placental barrier and have the potential to cause severe outcomes such as spontaneous abortion.
In conclusion, among the listed options, alcohol is the substance that can pass through the placenta to the fetus.