IB Biology Lecture Notes - Water's Role in Biological Systems

Introduction

• Discussion with Henry Hadfield Owens about grades in IB Biology.
  • Formative grades are good due to classwork and homework.
  • Summative grades (exam scores) need improvement.
  • Advice: Study more to improve exam performance.

Water as a Molecule

• Properties: Water is a polar molecule with negative and positive ends.
  • Polarity due to electron pull differences between oxygen and hydrogen.
  • Known as the universal solvent due to its ability to dissolve many substances.

Solvation Process

• Key Terms:
  • Solvent: The substance doing the dissolving (water).
  • Solute: Particles being dissolved.
  • Salvation: Process of solutes dissolving.
• Mechanism:
  • Water's polarity allows it to dissolve polar molecules and charged atoms.
  • Water molecules surround ions or molecules like sodium, chloride, or glucose.
  • Hydrogen bonds in water are broken and reformed as molecules move.
  • Water molecules are attracted more to solutes than to other water molecules.

Water Movement in Cells

• Water moves freely in and out of cells via simple diffusion.
• Scenarios:
  • High external solute (Sugar) concentration causes water to move out of cells.
  • Water moves toward higher solute concentration.

Solution Types and Osmosis

• Types of Solutions:
  • Hypotonic: Low solute concentration.
  • Hypertonic: High solute concentration.
  • Isotonic: Equal solute concentration inside and outside.
• Osmosis: Movement of water from low to high solute concentration.

Experiments and Applications

• Plant and Animal Cells:

  • Plant cells withstand osmotic changes due to cell wall pressure (turgor pressure).
  • Animal cells burst in extreme hypotonic solutions; shrink in hypertonic solutions.

• Osmosis Experiment:

  • Example: Submerging potato tissue in solutions with different solute concentrations.
  • Observations on mass change due to water movement.

• Applications in Medicine:

  • Organ Transport: Use isotonic solutions (normal saline) to maintain tissue health.
  • Intravenous Fluids (IV): Isotonic to human blood to ensure balance.

Conclusion

• Understanding water movement and its solvation capabilities is crucial in biological systems and practical applications like medicine.
• Key concepts: Solvent/solute interactions, osmosis, and solution types.