a) Compare the differences between an artery and a vein. b) List and explain 2 features that allow capillaries to exchange substances efficiently.

a) Veins have a larger lumen and a thinner wall as they carry blood at a lower pressure than the blood in arteries. Due to this low pressure, veins have valves to assist with the continuous movement of blood. The higher pressure blood in the arteries means that their wall is more elastic and muscular when compared to the wall of veins. Arteries carry blood away from the heart whereas veins carry blood towards the heart.b) Capillaries have a wall which is only one-cell thick. This increases the surface area for substance exchange. The blood in capillaries moves slowly which increases the time frame for substance exchange to occur.