Water’s cohesive and adhesive properties mean that it is viscous, making it a useful lubricant in biological systems such as the synovial fluid which lubricates many vertebrate joints. Also the continuous column of water is able to move up the xylem because of cohesion between water molecules and adhesive between water and the walls and the xylem vessels. The cohesive forces between the water molecules furthermore means that it is not easily compressed, and thus it is and excellent medium for support. Important biological examples include the hydrostatic skeleton i.e. earthworm, the amniotic fluid and as a general supporting medium for large aquatic mammals such as whales.
Any substance which is polar attracts water molecules. The electrostatic attractions between polar water molecules and ions are greater than those between the anion and cation. Ions become hydrated in aqueous solutions. Such polar substances, which dissolve in water, are hydrophilic. Non-polar substances will not dissolve in water and are called hydrophobic. Hydrophobic molecules arrange themselves to expose the minimum possible surface area to the water molecules. This property is very useful as it allows water to act as a transport medium for polar solutes. For example transport via the blood and lymph in multicellular animals, and the removal of metabolic wastes such as urea and ammonia in urine.
Most cells can only tolerate a narrow range of temperatures because of the properties of the enzymes within them. There is three properties of water which hep to stabilise the temperature of calls.
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Water has a relatively high heat capacity which means it must absorb a relatively large amount of heat before its temperature will rise. The specific heat capacity of water is 4184J kg-1 K-1, which is much higher, compared to alcohol which is only 2520J kg-1 K-1. This property of water is very useful because our bodies are largely composed of water and 70% – 80% of our cells, are very thermostable, and thus less prone to heat damage by changes in the environmental temperatures.
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A large amount of heat energy, 2.26 MJ kg-1 K-1, must be absorbed by water turn it into water vapour. Organism can cool down when only a little of their water evaporates. This phenomenon is used extensively by mammals, via sweating, and reptiles, via gaping, and may be important in cooling transpiring leaves.
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The relatively large latent heat of fusion. Water at 0 oC must lose a relatively large amount of energy before it forms ice crystals.
At the surface of ponds or lakes, the cohesion between water molecules produces a surface tension. Things that are denser than water generally sink. The surface tension of water can make a solid-like surface and support relatively dense objects such as insects. The cohesion of water helps its molecules to stick together when they are pulled. This can be demonstrated by sucking water through a straw. The pressure inside the mouth lowers and the atmospheric pressure pushes the water up the straw. If water did not have hydrogen bonds this would not be possible. This is important for plants which pul up water from the ground.
When water cools down, the individual molecules slow down enough for each one to form its maximum number of hydrogen bonds. To do this the water molecules in liquid water must move further apart to give enough space for all four hydrogen bonds to fit in. as a result water expands was it freezes, so that ice s less dense than liquid water and therefore floats upon its surface. This insulates organism in the water below it, and allows the ice to thaw rapidly when temperatures rise.
The chemical reactions which occur inside cells are called metabolism and the chemical reactions involved in these reactions are called metabolites. Water is either used or released in many metabolic reactions. It is used in photosynthesis and digestions.
The weakness of individual hydrogen bonds means that individual water molecules continually jostle one another when in the liquid phase. This allows osmosis to take place.
Most of the human body is water. Substances with molecules of a similar mass to water, such as ammonia and methane, are all gases at room temperature but water is a liquid. It is the polarity of water molecules and the fact that they can from hydrogen bonds which is the key to water’s special properties. It boils at 100ºC and melts at 0ºC. Water is probably the fundamental reason for life on Earth. Every living thing depends on it to survive which is why water is so important. As well as being essential to life, water also has many other uses. Some of these include being a very good solvent, for washing or even as habitats and environments. Water's abundance and requirements towards life already make it special but there are even more properties of water as a result of the hydrogen bonds between water molecules that make water vital for living things
