Why does water have biological significance?

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trophyhunter1 eNotes educator| Certified Educator

Water is an amazing substance that can exist on Earth in three states-- solid, liquid and gas. One reason water has biological significance is that it is the universal solvent. Many chemicals can dissolve in water.Thus, the life function of transport in many organisms relies on water.  Water makes up most of the volume of our cells and is found in our blood plasma. Plants require water for photosynthesis and release it back to the environment via the process of transpiration(evaporation through the stomates). Humans also produce water as a waste product of respiration which returns to the environment every time we exhale. Water makes up most of the urine we produce and dilutes the waste urea, which is then excreted from the body, via the kidneys. An interesting fact about water is that in its solid state (ice) it is actually less dense then its liquid state. Picture a glass of water with ice in it. The ice floats at the top! This seems weird as all other substances are more dense as solids and less dense as liquids. However, this strange property of water allows ice to form on the surface of a lake and beneath that ice is the more dense liquid water. So, when a lake freezes in winter, everything below the ice is in liquid water which has a temperature greater than 0 degrees Celsius. This allows the plants and animals to stay alive during the cold winter months. Water is a truly amazing chemical.