Question

question 6
which of the following is/are least likely to pass through the placental wall because of their size?
○ carbon dioxide
○ water
○ salt
○ hormones

Explanation:

To determine which substance is least likely to pass through the placental wall due to size, we analyze the molecular/structural size of each option:

• Carbon dioxide ($\ce{CO_2}$) is a small gas molecule (linear, 3 atoms) and can diffuse easily.
• Water ($\ce{H_2O}$) is a small polar molecule and can pass via osmosis or diffusion.
• Salt (e.g., $\ce{NaCl}$) dissociates into ions ($\ce{Na+}$, $\ce{Cl-}$), which are small and can pass through ion channels or via diffusion.
• Hormones are typically larger molecules (e.g., protein - based hormones like insulin, or steroid hormones with more complex structures). Their larger size makes it harder for them to cross the placental wall compared to the other small molecules/ions.

Answer:

D. hormones