How Water’s Structure Explains Its Biological Importance

Water’s structure makes it polar and allows water molecules to form hydrogen bonds with one another. These properties explain why water is a solvent, helps control temperature, holds together in columns and takes part in biological reactions.

How its structure creates these properties

A water molecule has one oxygen atom bonded to two hydrogen atoms. Oxygen attracts the shared electrons more strongly than hydrogen does, so the oxygen end has a slight negative charge and the hydrogen ends have slight positive charges. This uneven distribution of charge is called polarity. The slightly positive hydrogen of one water molecule is attracted to the slightly negative oxygen of another, forming a hydrogen bond.

Why that matters to organisms

• Solvent: Water’s polarity helps it dissolve ions and many other polar substances. Dissolved substances can be transported in blood and in plant tissues, and can react in cells.
• Temperature stability: Water has a high specific heat capacity. A lot of energy is needed to raise its temperature because energy is used to disrupt hydrogen bonds. This helps keep temperatures in organisms and aquatic habitats relatively stable.
• Cooling: Water has a high latent heat of vaporisation. Evaporating water takes substantial energy away from a surface, so sweating and transpiration can cool organisms.
• Cohesion: Hydrogen bonds make water molecules stick together. This helps maintain continuous columns of water as they are pulled up through xylem in plants.
• Metabolism: Water is a reactant in hydrolysis, which breaks a bond in a larger molecule, such as during digestion. It is produced in condensation, which joins molecules together, such as when amino acids form a peptide bond.

A common exam mistake is to say that hydrogen bonds within a water molecule cause these properties. The oxygen–hydrogen bonds are within each molecule; hydrogen bonds form between water molecules.