Fetal blood flow and placental exchange Steps:

• Identify umbilical artery carries deoxygenated blood from fetus to placenta for gas and waste exchange.
• Note umbilical vein returns oxygenated blood from placenta to fetus.
• Compare gas concentrations: artery blood has high CO2 from fetal respiration, vein has low CO2 after placental removal.
• Confirm waste and nutrients: artery delivers high CO2 and urea to placenta, vein supplies low CO2 and high nutrients.

Why B is correct:

• Umbilical artery blood contains higher CO2 as it transports metabolic waste from the fetus to the placenta for elimination, per placental gas exchange physiology.

Why the others are wrong:

• A: Artery blood has lower oxygen than vein blood, which is oxygenated by the placenta.
• C: Artery blood has higher urea than vein blood, as the fetus excretes waste via the placenta.
• D: Artery blood has lower glucose than vein blood, since the placenta supplies glucose to the fetus.

Final answer: B