Arteries usually carry oxygenated blood and veins usually carry deoxygenated blood. This is true most of the time. However, the pulmonary arteries and veins are an exception to this rule. Pulmonary veins carry oxygenated blood towards the heart and the pulmonary arteries carry deoxygenated blood away from the heart.-khanacademy.com
If plants cant take in carbon because of deforestation then the carbon will just pollute the earth. Bacteria are known for putting nitrogen back into the system.
