The Biological Importance of Water.

Water has a high specific heat capacity allowing it to maintain constant temperatures. In water the approximate value is 4200J/kg°C.
This means that to raise the temperature of 1kg of water by 1°C, 4200J of
energy are required, so the temperature of water is not easily changed.
A large mass of water, such as an ocean, will heat up slowly during the day, and
cool slowly at night, so its temperature does not change much.
This provides an ideal habitat for marine organisms, with only small variations
in temperature. Mammals sweat when their body temperature is too high.
Sweat consists of mainly water, and the large amount of energy required to
evaporate the sweat from the surface of the organisms is taken from the organism,
thus giving a large cooling effect. Plants also lose water in a process called
transpiration, and this helps water uptake by the roots, and has an effect on the
temperature of the plant, and helps to keep this from rising too high.

        Water is also used to split up molecules by adding water. This is called hydrolysis and is essential to animals and plants because it allows them to utilise stored foods which are in long chains by breaking off smaller molecules.
Respiration produces water as a by-product. A large amount of energy is produced by oxidising hydrogen, which contains so much energy it is an explosive gas, into water. Photosynthesis uses water as a source of hydrogen atoms which are needed to produce glucose which is then stored in the plant cells as starch or used for respiration. Without water these two essential reactions would not occur and life would not be able to continue on earth.

An important property of water is also it's transparency, it allows sunlight to pass through it so aquatic plants can photosynthesis and on a larger scale, allow life on earth to begin, since life started in the oceans with small organisms which relied on sunlight for the reaction photosynthesis to take place.

As a result of water's strong hydrostatic forces water is incompressible. This provides support for soft bodied creatures such as worms, slugs and jellyfish which therefore do not require a supporting skeletal system. Water allows cells filled with water to become turgid and due to it's incompressibility plants can support themselves.

        Water molecules are very cohesive, sticking together because of the presence of hydrogen bonds. This cohesive property is important in the transport of materials in solution within organisms. The cohesive properties of water allows plants to pull up water through xylem vessels from the roots to the leaves, this is called the transpiration stream. It also means that the water molecules where the water meets the air will be tightly held together and the water molecules below them to form elastic film known as surface tension. Small creatures can get stuck in the surface water because they cannot break the water surface tension, creatures like water skaters can move across the surface of the water without sinking as they have a hydrophobic foot which stops them from breaking the surface tension.

Bones meet at joints, and at these joints lubrication must be provided to
make sure the bones do not scrape against each other causing damage,
and enabling free easy movement by reducing friction.
A synovial membrane at joints encloses a fluid called synovial fluid,
which acts at the lubricant. Water is a major part of this fluid.

        Finally water also allows for insulation to happen.  Waters maximum density is at 4.c as the temperature of a body of water, such as a pond drops the cooler water is at the surface and when it freezes, ice forms on the surface. This ice then insulates the water below, enabling aquatic organisms to survive. This is especially important in cold climates and where there are cold seasons.