Due to the cohesive forces between water molecules it is an ideal medium for support as it is very hard to compress. An example of its use for support is the amniotic fluid, which supports and protects the mammalian foetus.
The weak nature of single hydrogen bonds means water molecules can move easily allowing the uptake and movement of water (osmosis) to happen.
As water has cohesive and adhesive properties it is viscous. This makes it an effective lubricant in biological systems. For example synovial fluid lubricates the joints of many vertebrates.
A large amount of energy is required to increase the temperature of water. Bodies largely composed of water are thermostable, therefore less prone to heat damage caused by changes in the environment temperature.
Water is balanced at the Earth’s temperature so the water cycle of evaporation, transpiration and precipitation is sustained.
In plants a continuous channel of water is able to move up the xylem due to the cohesion between water molecules and adhesion between water and the walls of the xylem vessels.
Water is a transport medium for polar solutes. For example it removes metabolic waste such as urea and ammonia in urine.
Water as a solvent
Polar molecules and ions dissolve in water. Polar molecules include sugars and glycerol, which have free hydroxyl groups (OH) projecting from the molecule. Polar molecules carry an unevenly spread charge. This makes some parts of the molecule positive and some parts negative. Water is also a molecule.
When sugar is mixed with water the small positive charge on the hydrogen of the water molecule is attracted to the small negative charge on the of the sugar. In a similar way the oxygen in water is negatively charged and is attracted to the charged part of the sugar molecule. These forces of attraction make the water molecules stick to the sugar with hydrogen bonds. This separates the sugar molecules. The sugar therefore dissolves. Waters’ ability to act as a solvent allows the dissolving chemical to move about more freely and react together. We say that the sugar molecules are hydrophilic.
Non polar molecules like lipids are insoluble in water. If lipids are mixed with water the water molecules stick to each other. This pushes the non polar (lipid) molecules together in a biob or a . This is a hydrophobic interaction.
Thermal Properties, Density and Freezing
- Why is an unusual amount of energy needed to raise the temperature of water?
A large amount of energy is needed because hydrogen bonding restricts the movement of water molecules.
How does this property of water help living things?
It creates a more stable habitat for water dwelling organisms and it minimises internal changes in body temperature making it easier to maintain a stable body temperature.
- Why is evaporation of water particularly effective as a means of cooling the body?
The high latent heat of vaporisation of water means that a body can be considerably cooled with a minimal loss of water.
What makes it difficult for water to freeze?
Ice is less dense than water. This means ice floats insulating the water beneath it therefore preventing large amounts of ice being formed.
- Water is less dense as a solid than as a liquid. Give 2 reasons why this is advantageous.
It helps to prevent whole oceans and lakes freezing and increases the chance of water dwelling organisms surviving.
- What property of water leads to high surface tension and cohesion?
Water molecules tend to stick to each other because of the hydrogen bonding between them.
Properties of water and their biological significance
