4.1 - Water

Water is one of the most abundant and important compounds ever existed on the Earth. It is a tasteless, odorless and transparent inorganic substance. It is essential to all living organisms.

Figure 1 - The chemical formula of water is H₂O. 2 hydrogen atoms are joined to 1 oxygen atom. Hydrogen bonds can form between adjacent water molecules.

Properties of Water and Its Importance in a Cell

The unique properties of water include:

• Polarity
  • Water molecules are polar due to the partial positive charge of hydrogen atoms and the partial negative charge of oxygen atom.
  • Its ability to form hydrogen bonds allows water to act as a universal solvent. This means that water is capable of dissolving more substances than any other solvents.
  • Dissolution of the solutes such as glucose and ions allow the substances to be transported across the plasma membrane.
• Strong adhesive and cohesive forces
  • The adhesive and cohesive properties of water molecules facilitate the movement of water along narrow spaces such as in the xylem vessels.
  • Water can stick and clump together to form droplets due to cohesive forces. The cohesion holds the hydrogen bonds together to create surface tension on the water surface.
  • At the same time, water is also very adhesive. It can stick well to other surfaces. Due to its polarity, it is attracted to other substances that have charges.
• Specific heat capacity of water
  • The specific heat capacity of water is 4.2 kJ kg⁻¹ °C⁻¹. This means that it takes 4.2 kJ of heat to raise the temperature by 1°C.
  • This is important because water makes up about 70% of the Earth's surface. This property signifies that it can absorb a lot of heat energy without a sharp rise in temperature.
  • Besides, this also helps living organisms to regulate their body temperature during hot weather.

Figure 2 - Cohesion and adhesion give water molecules 'the stickiness' property. This natural surface tension helps insects to walk or stay on water surface.