Understanding Water: The Molecule of Life

Introduction

• Life's intricacies require knowledge of water.
• First cells were created in water; it's the medium for life processes.

Molecular Structure of Water

• Composed of 3 atoms: 1 oxygen and 2 hydrogen.
• Water molecules are polar due to asymmetrical structure and polar covalent bonds.
  • Results in partial negative and positive charges.
  • Electrons closer to oxygen due to its higher electronegativity.

Importance of Water's Polarity

• Polarity leads to hydrogen bonding.
  • Oxygen's negative end attracts hydrogen's positive end of another water molecule.
  • Hydrogen bonds are weak but significant.

Properties of Water

Cohesion

• Water molecules stick to each other due to polarity and hydrogen bonds.
• Plays a role in biological systems, like transpiration in plants.
  • Cohesion helps water move against gravity in xylem.
  • Water striders use cohesion to "walk on water" due to surface tension.

Adhesion

• Water molecules stick to other surfaces.
• Occurs on polar surfaces, like soil and plant xylem.
  • Supports capillary action in soil and water movement in xylem.

Solvent Properties

• Water dissolves various particles due to polarity.
• Known as a universal solvent.
  • Sodium chloride dissolves due to attraction to water's charges.
• Important for metabolism and transport in organisms.
  • Dissolves ions for cellular reactions and transport in blood.

Other Physical Properties

Specific Heat

• Water has a high specific heat, requiring more energy to change temperature.
  • Maintains stable temperatures in organisms.

Thermal Conductivity

• Water transfers heat efficiently.
  • Seen in blood, helps dissipate heat in animals like the fennec fox.

Buoyancy

• Ability to float depends on density.
  • Organisms' density close to water's allows floating.
  • Algae uses trapped oxygen for buoyancy.

Viscosity

• Describes ease of flow.
  • Water flows easily; viscosity increases with solutes.
  • Important for ocean organisms due to seawater's viscosity.

Organism Comparison

Black-throated Loon (Gavia arctica) vs. Ringed Seal (Pusa Hispida)

• Seal spends more time in water, impacted more by water's properties.
  • Greater energy expenditure and heat loss in water.
  • Adaptations like fur help in temperature regulation.

Conclusion

• Understanding water's properties is crucial for biology.
• Important for the IB exam to compare organism adaptations to water's properties.