Properties of Water

Water is important because it is a major component of cells. It's molecules have an imbalance of charge (dipolar) and this generates hydrogen bonding between them.

Water is a polar solvent:

• Oxygen in water has a negative charge and hydrogen bears a relative positive charge.
• Ions such as those found in sodium chloride (NaCl) can bind respectively to the oxygen side or to the hydrogen side
• Thus, the salt is soluble and dissolves.
• Non-polar molecules like lipids do not dissolve in water and tend to be pushed together by it.
• This is important in hydrophobic interactions in protein structure and in membrane structure.
• Due to it's ability to dissolve so many molecules, water is an important transport medium in animals and plants.

Thermal properties

• Water molecules are attracted to one another by hydrogen bonds, restricting the movement of the molecules.
• A relatively large amount of energy is required to increase the temperature of water.
• Due to their high water content, bodies of organisms are also slow to change temperature which makes maintaining a stable body temperature easier.
• Water has a large latent heat of vaporisation.
• This means it can produce a cooling effect when it evaporates without needing much of it, thus risking excessive water loss.

Density and freezing properties

• Waters solid form is less dense than it's liquid form.
• Below 4°c the density of water starts to decrease, so ice floats on water and insulates the water below it.

High surface tension and cohesion

• Water molecules tend to stick together.
• When you have long water columns e.g. transport cells in plants, it's a continuous stream that's difficult to break.
• This property is cohesion.
• It's also the reason behind water's tight surface against air, called surface tension,
• Surface tension enables small organisms e.g. pond skaters to exploit water as a habitat.