AP BIOLOGY

Detailed explanation-1: -Veins have valves to prevent this backflow of blood. Valves ensure that blood flows only in one direction through veins. Therefore, veins have valves, not the arteries.

Detailed explanation-2: -Blood flow within your legs occurs mainly through the deep venous system. Femoral veins typically have between one to six vein valves, and popliteal veins often contain between zero to four valves. Valves in veins are bicuspid, meaning they have two flap-like structures that regulate blood flow.

Detailed explanation-3: -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.

Detailed explanation-4: -Background: The ophthalmic and facial veins are frequently stated to be devoid of valves, facilitating the spread of infection from the mid-face to the cavernous sinus. Methods: Twelve superior and eight inferior ophthalmic veins together with 13 angular and facial veins were harvested from adult cadavers.

Detailed explanation-5: -So, the correct option is ‘Veins’.