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Circulatory System – Biology and Evolution

By |2018-04-16T08:24:44+00:00May 26th, 2017|Biology|

Circulatory system: A dog heart What is the circulatory system? The circulatory system takes food and air from outside your body and brings it all over your body so that all your cells get the food and oxygen they need to stay alive. The earliest cells, about 3.8 billion years ago, didn't need [...]