AP BIOLOGY

Detailed explanation-1: -Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls. Therefore, Option A is correct.

Detailed explanation-2: -Veins have thicker walls than capillaries. Veins use valves to transport blood towards the heart, but capillaries don’t have valves.

Detailed explanation-3: -Since the blood pumped from the heart into the arteries flows at higher pressure than the blood in veins, hence arteries need to have thicker walls or else the high blood pressure might cause them to burst. Q. Why do veins have valves while arteries do not?

Detailed explanation-4: -Arteries and arterioles have relatively thick muscular walls because blood pressure in them is high and because they must adjust their diameter to maintain blood pressure and to control blood flow.

Detailed explanation-5: -Unlike arteries, veins contain valves that ensure blood flows in only one direction. (Arteries don’t require valves because pressure from the heart is so strong that blood is only able to flow in one direction.) Valves also help blood travel back to the heart against the force of gravity.