How do animals breathe? Respiration, Evolution, 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 [...]
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 [...]
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 [...]