Water's Vital Role in Life and Biological Processes

Water: The Foundation of Life

Life on Earth began in water, evolving over 3 billion years before conquering land. Water continues to be essential for all living beings.

Water's Essential Role in Biological Systems

The unique properties of cell membranes are due to their particular structure, which in turn is due to the tendency of the phospholipids that compose them to form bilayers in aqueous media.

• Water is Essential for Life: It is a constituent of cells (its percentage depends on cell type and physiological state), provides a means of transport for solutes over short and long distances, and is involved in cell metabolism as a substrate, product, or reagent.
• Turgor: A feature of plant cells where water exerts pressure on the cell wall. It is necessary for plant cell growth and the opening of stomata, which allows the capture of CO2 needed for photosynthesis.
• Osmosis: The diffusion of water through a semipermeable membrane.

Water's Unique Physical Properties

1. Low Compressibility: This property allows for turgor and cell expansion in plant cells.
2. Excellent Solvent: Water is a good solvent for ions and polar substances, promoting essential solute transport throughout the body.
3. High Specific Heat and Heat of Vaporization: These properties favor thermal regulation.
   • Specific Heat: The energy required to raise the temperature of a substance by a certain amount.
   • Heat of Vaporization: The energy required to change a substance from a liquid to a gaseous state at a constant temperature and pressure.
4. Liquid State Range: Water remains liquid between 0°C and 50°C, a temperature range in which most metabolic processes occur.
5. Density Anomaly: Water is more dense in its liquid state than in its solid state, allowing aquatic life to survive under ice.

Molecular Characteristics and Interactions

The water molecule is polar due to an unequal distribution of charges resulting from electronegativity differences. This polarity leads to several crucial properties:

• Cohesion: The attraction between water molecules in a liquid state, based on the establishment of hydrogen bonds.
• Adhesion: The attraction between a liquid phase and a solid phase.
• Surface Tension: The energy per unit area that must be applied to a liquid to expand its surface. The high surface tension of water allows some insects to walk on its surface.

Water Movement and Energy Potential

The movement of water from deeper roots to the top of the canopy is the realization of work. Water chemical potential quantifies the free energy per mole of water.

• Water Potential: The water chemical potential, based on pure water at atmospheric pressure and divided by the partial molar volume of water.
• Transpiration: The process by which plants release water vapor into the atmosphere.