The correct option is (c) 1 and 3 only.
Explanation
The circulatory system consists of blood vessels-arteries, veins, and capillaries-that transport blood throughout the body. Veins are specifically designed to return blood from various body parts back to the heart under lower pressure conditions compared to arteries.
Statement-wise Analysis:
- Statement 1 is Correct: Veins are blood vessels that carry blood from body organs towards the heart. Generally, this blood is deoxygenated and rich in carbon dioxide. The only exception is the pulmonary vein, which carries oxygenated blood from the lungs to the heart. Since the statement uses the qualifier "generally," it is factually accurate.
- Statement 2 is Incorrect: Unlike arteries, where blood flows under high pressure, blood pressure in veins is low. To prevent the backward flow of blood due to gravity or low pressure, veins are equipped with valves. Arteries, conversely, generally do not possess valves (except at the base of the aorta and pulmonary artery).
- Statement 3 is Correct: Arteries have thick, elastic walls to withstand the high pressure of blood pumped directly from the heart. In contrast, veins have thinner and less elastic walls because the blood flowing through them is under much lower pressure.
Key Takeaway:
Veins are thin-walled vessels that generally transport carbon dioxide-rich blood towards the heart and possess valves to ensure unidirectional flow, preventing backflow.