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Name:  Helen
Status: student
Age: 14
Location: N/A
Country: N/A
Date: 9/6/2004

Please can you tell me why smaller animals have a faster pulse and respiratory rate compared to larger animals?

Because the ratio of surface to volume in their large blood vessels and airways is larger for small animals than for large animals.

At the surface of a blood vessel, blood hardly moves because it is in contact with the wall. So the more surface you have, the harder it is to pump blood. This means small animals have to work harder that large animals to get blood to each of their cells.

But large animals and small animals use the same kind of pumping machinery (i.e., muscle fibers), so the only thing small animals can do to make up the difference is to run their pumps faster.

Tim Mooney

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