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PBS
How Plants Caused the First Mass Extinction
In the middle of the Cambrian, life on land was about to get a little more crowded. And those newcomers would end up changing the world. The arrival of plants on land would make the world colder, drain much of the oxygen out of the...
Khan Academy
Khan Academy: Fetal Circulation: Hypoxic Pulmonary Vasoconstriction
Watch how blood gets diverted away from alveoli with low oxygen levels. Rishi is a pediatric infectious disease physician and works at Khan Academy. [9:13]