The correct option is (a).
Explanation
The human circulatory system relies on a network of blood vessels-arteries, veins, and capillaries-to transport blood, nutrients, and gases throughout the body. These vessels function based on specific structural hierarchies and directions of flow.
- Statement 1 is correct: Arteries carry blood away from the heart to various tissues. Upon reaching an organ or tissue, arteries branch into smaller vessels called arterioles, which further divide into extremely thin-walled vessels known as capillaries. This division ensures that blood comes into close contact with individual cells for the exchange of substances.
- Statement 2 is incorrect: Capillaries do not join to form arteries. After the exchange of materials (such as oxygen, nutrients, and waste products) occurs at the cellular level, capillaries reunite to form venules, which subsequently join together to form veins.
- Statement 3 is incorrect: By definition, arteries carry blood away from the heart to the body's tissues. Veins collect blood from different parts of the body and carry it back to the heart. While most arteries carry oxygenated blood and most veins carry deoxygenated blood (with the exception of pulmonary vessels), the direction of flow relative to the heart is the definitive distinction.
Key Takeaway: The structural sequence of blood flow in the systemic circulation is: Heart → Arteries → Arterioles → Capillaries → Venules → Veins → Heart.