Biological Importance of Water and Mineral Salts

Functions and Properties of Water

These properties are due to the polarity of the water molecule, which provides its solvent power, and the existence of hydrogen bonds.

Solvent Power

Thanks to the polarity of the molecule, water can be interposed between the ions in the crystal lattices of ionic compounds. This decreases the attraction between them and causes them to separate (dilution).

Liquid at Room Temperature

The great strength of cohesion between its molecules ensures that water remains liquid at normal temperatures. Thanks to this, water acts as a carrier in the body.

Incompressible Liquid

Due to the high degree of cohesion, the volume of liquid water does not decrease even when applying pressure.

Capillarity

Water molecules are held together by hydrogen bonds, giving them a very high degree of cohesion. When combined with adhesion to the surface of other structures, water can move up along narrow channels.

High Surface Tension

Molecules on the surface are subject only to the attraction of the internal water molecules, which creates a strong cohesive force.

High Heat of Vaporization

It is necessary to break the hydrogen bonds (which requires energy) to transition from a liquid to a gas.

Lower Density of Ice than Liquid Water

Usually, when a liquid cools, its density increases; however, ice is less dense than liquid water.

Functions of Mineral Salts (Inorganic Biomolecules)

Mineral salts are inorganic compounds that may be soluble or insoluble in water, forming solid structures in living organisms.

• Constitution of hard structures: Used for support and protection.
• Physiological and biochemical functions: Involving ions such as Na, K, and Mg.
• Maintenance of osmotic concentrations: Biological processes dependent on the solute concentration in water are called osmotic processes.

Osmosis and pH Balance

When two separate solutions of different concentrations are divided by a semipermeable membrane (which does not let the solute through but allows the solvent), the passage of solvent occurs from the more dilute solution (hypotonic) to the more concentrated one (hypertonic).

When water passes into the hypertonic solution, it dilutes it. This process ends when the two solutions reach equal concentrations (becoming isotonic). To prevent the passage of water, osmotic pressure is applied.

Maintenance of pH

pH 7 represents neutral solutions, while pH < 7 is acidic. To avoid pH changes, buffer systems composed of a weak acid and its base are involved. These systems act as H+ donors or acceptors to compensate and maintain the pH (e.g., phosphate and bicarbonate buffers).