Some of the properties of water that make it essential for
life are the following:
As far as inorganic substances are
concerned apart from water only mercury and liquid ammonia can exist as liquids at the
temperature and pressure that prevails on Earth. The fact that water can remain as a
liquid is essential for its use as a medium for the transfer of ions within living
cells.
Water has a very high specific heat. As the amount
of heat required to change the temperature of water is very large it allows water to
remain in the liquid phase over a very wide temperature range. Under normal pressures
water can remain in the liquid phase from 0 degree Celsius to 100 degree Celsius. No
other known substance can remain a liquid in this wide a temperature
band.
Another unique property of water is that unlike most
other substances, the density of water as a solid is less than that of water in the
liquid phase. This makes ice float on water. The low conductivity of ice allows water
below it to remain liquid and at a temperature that can sustain life. In regions of the
Earth where temperatures fall far below 0 degree Celsius, life is able to exist in water
due to the sheet of ice floating above it.
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