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the main nitrogenous waste product of protein metabolism.
energy resources such as coal and oil, which are being used up much more quickly than they can...
an atmospheric gas made of three oxygen molecules bonded together (O3).
an individual who donates an organ for the purpose of transplanting it into another person in an...
a hormone produced by the adrenal glands which helps to maintain the balance of sodium in the...
a species that has a large effect on its environment relative to its abundance and plays an...