Lecture Notes: The Role and Properties of Water in Life

Introduction

• Importance of understanding molecular components of life
• Water as a fundamental component for life
  • First cells formed in water

Structure of Water

• Composed of three atoms: 1 oxygen, 2 hydrogen
• Water molecules are polar
  • Asymmetrical structure
  • Polar covalent bonds
  • Unequal charge distribution (Oxygen: partial negative, Hydrogen: partial positive)

Polarity and Molecular Bonds

• Concept of polar vs nonpolar molecules
  • Methane example (nonpolar)
• Hydrogen bonds in water
  • Attraction between negative oxygen and positive hydrogen of different water molecules

Important Properties of Water

Cohesion

• Ability of water molecules to stick together
• Hydrogen bonds maintain cohesion
• Biological significance:
  • Plant water transport via xylem
  • Transpiration and gravity resistance
  • Insects like water striders utilize surface tension

Adhesion

• Attraction of water molecules to other surfaces
• Polar surfaces attract water (e.g., soil, plant xylem)
• Capillary action explained

Solvent Properties

• Water as a universal solvent
  • Ability to dissolve many substances
  • Hydrophilic substances like salt explained
• Biological uses:
  • Metabolism and reactions
  • Transport medium (e.g., xylem, blood plasma)
• Hydrophobic molecules and their roles
  • Example: Phospholipid bilayer in cell membranes

Other Physical Properties of Water

Specific Heat

• Water's high specific heat capacity (4.186 J/g°C)
  • Energy required to break hydrogen bonds
  • Stabilizes temperatures for organisms

Thermal Conductivity

• Water's ability to transfer heat
• Example: Fennec fox dissipating heat via blood vessels

Buoyancy

• Ability of substances to float
• Density-related property
  • Example: Algae buoyancy through trapped oxygen

Viscosity

• Describes flow based on internal friction
• Water vs other substances (e.g., tree sap)
• Importance in marine organisms

Comparative Study for IB Exam

• Organisms: Black-throated loon (Gavia arctica) and Ringed Seal (Pusa Hispida)
• Impact of water's physical properties on each:
  • Seal: More interaction with water, affected by viscosity and thermal conductivity
  • Adaptations like fur for heat regulation

Conclusion

• Understanding water's properties is essential for biology
• Important for exam preparation: comparisons and applications