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How do animals breathe? Respiration, Evolution, Biology

By |2018-04-21T11:56:44+00:00May 27th, 2017|Biology|

Fish gills The first cells, which evolved about 3.8 billion years ago, needed carbon dioxide to live and not oxygen. They needed the carbon dioxide to help them break down molecules to get energy out of them, and they were able to get the carbon dioxide they needed from the oceans they lived [...]

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 [...]