-  Composition of blood is regulated - Volume of water in blood is kept constant - PH is kept at a constant level - Kidneys help regulate blood pressure - Kidneys stimulate the making of red blood cells - Calcium levels are maintained.  What might be the first step of the process?
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Answer: Kidneys filter waste out of blood


-  May come from different sources - The gases remain trapped in the atmosphere - Through the suns light the gases hold in heat and energy - Trap them in our atmosphere - The earth may become warmer this way.  What might be the first step of the process?
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Answer: Several types of gases form in the atmosphere


-  Is exposed to air - A chemical reaction occurs - The iron starts to oxidize - The iron starts to rust.  What might be the first step of the process?
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Answer: