3. W a t e r !!!! Water is a molecule composed of two hydrogen atoms (H) and one of oxygen, so its chemical formula is H2O. This bond is so strong that for a long time it was believed that water was an element and not a compound.
4. Human Excretion ! regulate the chemical composition of body fluids by removing metabolic wastes and retaining the proper amounts of water, salts, and nutrients. Components of this system in vertebrates include the kidneys, liver, lungs, and skin.
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