Placental Nutrient and Waste Exchange

Steps:

• X represents fetal blood entering the placenta, carrying waste from the fetus.
• Y represents fetal blood exiting the placenta after exchange with maternal blood.
• CO2 and urea, as fetal waste products, diffuse out to maternal blood, decreasing from X to Y.
• Glucose, a nutrient, diffuses in from maternal blood, increasing from X to Y.

Why B is correct:

• In placental diffusion, fetal waste (CO2 from respiration, urea from metabolism) moves down concentration gradients from fetal to maternal blood, per Fick's law of diffusion.

Why the others are wrong:

• A: Glucose concentration rises from X to Y as it's absorbed by the fetus.
• C: Glucose concentration rises from X to Y as it's absorbed by the fetus.
• D: Glucose concentration rises from X to Y as it's absorbed by the fetus.

Final answer: B