1.6.3 The Properties of Water

Below are the key properties of water:

1. Polar Molecule:

• Water is a polar molecule, meaning it has an uneven distribution of charge.
  • The oxygen atom is more electronegative and attracts the electrons more strongly than the hydrogen atoms.
  • As a result, the oxygen end of the molecule is slightly negative, and the hydrogen end is slightly positive.
• This polarity allows water molecules to form hydrogen bonds with each other, causing them to stick together.

2. Metabolite:

• Water plays a key role in many metabolic reactions:
  • It is involved in condensation reactions (where water is produced, e.g., forming polymers like proteins and carbohydrates).
  • It is also involved in hydrolysis reactions (where water is used to break down large molecules into smaller ones, e.g., digestion).

3. Solvent:

• Water is an excellent solvent due to its polarity. This means it can dissolve a wide range of substances, such as:
  • Gases (e.g., oxygen and carbon dioxide).
  • Enzymes and waste products (e.g., ammonia, urea).
• This property allows water to transport important molecules around organisms and helps in the diffusion of gases.

4. High Specific Heat Capacity:

• Water has a high specific heat capacity, meaning it can absorb a lot of heat before its temperature rises significantly.
  • This is because of the hydrogen bonds between water molecules, which must be broken to increase the temperature.
• This property helps minimise temperature fluctuations in organisms and environments, acting as a temperature buffer and providing a stable environment for cellular processes.

5. High Latent Heat of Vaporisation:

• Due to hydrogen bonding, water requires a significant amount of energy to break the bonds between molecules and turn from liquid to gas.
  • This gives water a relatively high latent heat of vaporisation.
• This property is beneficial for cooling the body (e.g., through sweating or panting) with minimal loss of water.

6. Cohesion and Surface Tension:

• Water exhibits strong cohesion, meaning water molecules stick together due to hydrogen bonding.
  • This is important for processes like the transport of water in plants (e.g., through the xylem).
  • Cohesion supports the column of water, allowing it to move upwards through narrow tubes.
• High surface tension at the water-air boundary is due to the strong cohesion between water molecules, allowing small organisms (e.g., water striders) to walk on water without sinking.