The carbon that plants need for photosynthesis comes from (carbon dioxide gas in the atmosphere)
The remains of fossils give scientists clues as to what the world may have been like a long tome ago. If fish fossils are found on the side of a mountain, there may have been a lake there. If a skeleton is found, they can decide what creature it was.
Answer:
Blood taken from an artery in the leg is oxygenated while blood taken from a vein in the leg is deoxygenated.