Why do veins have valves?
a)to maintain volume of blood
b)to prevent escape of carbon-dioxide gas
c)to prevent mixing of pure and impure blood
d)All of these
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1
Answer:
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.
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Answer:
a) to maintain volume of blood
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