The correct option is A. Explanation of the Correct Answer (A) Statement A: Blood in the pulmonary artery is richer in oxygen content than blood in the pulmonary vein. This statement is NOT true. In the mammalian circulatory system, the pulmonary artery carries deoxygenated blood from the heart to the lungs, where carbon dioxide is exchanged for oxygen. Therefore, the blood in the pulmonary artery has a lower oxygen content compared to the blood in the pulmonary vein, which carries oxygenated blood back from the lungs to the heart. To clarify: - Pulmonary Artery: Carries deoxygenated blood (low in oxygen, high in carbon dioxide). - Pulmonary Vein: Carries oxygenated blood (high in oxygen, low in carbon dioxide). Explanation of Other Options Statement B: The blood in the hepatic portal vein is the richest in food substance. This statement is true. The hepatic portal vein carries blood from the gastrointestinal tract and spleen to the liver. This blood is rich in nutrients absorbed from food, such as glucose, amino acids, and other metabolites. The liver processes these nutrients before they enter the general circulation, making this statement accurate. Statement C: Blood flow is controlled by valves in the veins. This statement is true. Veins have one-way valves that prevent the backflow of blood, ensuring that it flows in the correct direction toward the heart. This is particularly important in the limbs, where blood must travel against gravity. The contraction of surrounding muscles also helps push blood through the veins, but the valves are crucial for maintaining unidirectional flow. Statement D: Arteries are generally thicker and larger than veins. This statement is true. Arteries have thicker walls than veins because they need to withstand higher pressure from the blood being pumped directly from the heart. The muscular and elastic walls of arteries allow them to expand and contract with each heartbeat. In contrast, veins have thinner walls and a larger lumen (the hollow part of the blood vessel) to accommodate the lower pressure of blood returning to the heart. Summary of Key Points

• Pulmonary Artery vs. Pulmonary Vein: The pulmonary artery carries deoxygenated blood (low in oxygen), while the pulmonary vein carries oxygenated blood (high in oxygen).
• Hepatic Portal Vein: This vein carries nutrient-rich blood from the digestive organs to the liver.
• Valves in Veins: These structures ensure one-way blood flow back to the heart, preventing backflow.
• Arteries vs. Veins: Arteries have thicker walls and are smaller in diameter compared to veins, which have thinner walls and larger lumens.

Revision Summary

• The pulmonary artery carries deoxygenated blood; the pulmonary vein carries oxygenated blood.
• The hepatic portal vein is nutrient-rich, transporting blood from the digestive tract to the liver.
• Valves in veins prevent backflow and ensure proper blood flow to the heart.
• Arteries are thicker and more muscular than veins, designed to handle higher blood pressure.