No, they do not. They turn CO2 and water into oxygen and glucose.
Apart from that . . .
Global Warming on Free Republic here, here and here
PING to #14.
Only he young ones and those only in the day time. At night they wastefully burn glucose polluting the world with greenhouse CO2.. Forget virgin forests, they got so much greenhouse rotting going on that they're net polluters. The oxygen we breath comes from the algae in the ocean.