Osmosis | DP IB Biology Revision Notes 2023

Solvation & Water

• Solutions consist of a solute dissolved in a solvent.
• Water is an excellent solvent due to its dipolar nature:
  • Hydrogen side: slightly positive
  • Oxygen side: slightly negative
• Water forms hydrogen bonds with other polar solute molecules and ions.
• Hydrogen bonding is crucial for water's function as a solvent.
• Solvation is the interaction between a solvent like water and a solute.

Key Diagrams

• Hydrogen bond and electron arrangement: Shows how water molecules are dipolar.
• Dipolar nature of water: Demonstrates how water molecules form hydration shells around solutes.

Water Movement in Solutions

• Cells are surrounded by a partially permeable membrane.
• Osmosis is the diffusion of water across a partially permeable membrane.
  • Movement from less concentrated (dilute) to more concentrated solutions.
  • Water moves down its concentration gradient.
• The cell membrane allows small molecules (water) through while blocking larger molecules (solutes).

Key Concepts

• Osmosis: Net movement of water from lower solute concentration to higher concentration through a partially permeable membrane.
• Hypotonic Solution: Lower solute concentration outside; water moves into the cell.
• Hypertonic Solution: Higher solute concentration outside; water moves out of the cell.
• Isotonic Solution: Equal solute concentration; no net movement of water.

Tonicity Diagrams

• Tonicity of solutions: Visual representation of water movement based on solute concentration.

Examiner Tips

• Water molecules are always in motion due to kinetic energy:
  • In an isotonic solution, there is no net movement, but water still moves.

Additional Resources

• More Exam Questions and Flashcards available related to water potential and osmosis to aid in further study.