The Importance of Water in Human Biology

Key Points

• Survival Rule of Three: Humans can survive 3 weeks without food, but not 3 days without water.
• Biological Functions:
  • Composition: Human biochemistry is 60% water.
  • Systems Involved:
    • Integumentary to Digestive: Water aids from food ingestion to metabolism.
    • Urinary: Carries toxins and waste through urine.
    • Skeletal and Muscular: Acts as a lubricant.
    • Cellular Level: Allows cells to grow, reproduce, and survive.
    • Neurosystem: Facilitates hormone and neurotransmitter flow.
    • Respiratory: Expels oxygen and carbon dioxide.
    • Temperature Regulation: Maintains homeostasis.

Biochemistry of Water

• Molecular Structure:

  • Composition: One oxygen and two hydrogen atoms (H₂O).
  • Geometric Structure: Tetrahedral "V-shape" with bond angle of 104.5°.
  • Polarity: Water is a polar molecule.

• Electronegativity:

  • Oxygen: Higher electronegativity than hydrogen.
  • Charge Distribution: Partially negative oxygen and partially positive hydrogen.

Hydrogen Bonds

• Emergent Properties:
  • Formation: Created by the attraction between partially charged oxygen and hydrogen.
  • Characteristics: Weaker and longer than covalent bonds, can connect with up to four other molecules.

Properties of Water

• Universal Solvent: Capable of dissolving various substances.
• Adhesion and Cohesion: Enables water to stick and cling.
• Lesser Density: Facilitates surface tension and insulation for aquatic organisms.
• Capillary Action: Helps in water transport in plants.
• Neutral pH: Maintains human body homeostasis.
• High Heat Capacity: Allows evaporation and cooling.
• Surface Tension: Resists breaking among surfaces.
• Hydrophilic and Hydrophobic Properties: Separates polar and non-polar molecules.

Water as a Solvent: Illustration

• Dissolution Process:

  • Salt in Water: Sodium molecules dissolve, separate, and mix with water.
  • Sugar in Water: Sucrose dissolves slowly, forming fructose.
  • Dynamic Motion: Constant movement powered by polarity.

• Microscopic View:

  • Random Movement: Driven by polarity.
  • Interaction with Solutes: Sodium chloride and fructose dissolve, displaying continuous motion.

Conclusion

• Dynamic Nature: The motion and polarity define water’s role as a universal solvent.