Lecture Notes: Osmosis

Key Concepts

• Osmosis: Diffusion of water (H2O) across a permeable membrane.

  • Requires a semi-permeable membrane.
  • Unlike solutes, water moves in osmosis, not the solutes.

• Diffusion: Molecules move from high concentration to low concentration.

  • Applies to osmosis with a focus on water movement.

Osmosis Scenario

• Experiment Setup:

  • U-tube with a semi-permeable membrane, impermeable to glucose.
  • Side A: 10 glucose molecules.
  • Side B: 3 glucose molecules.

• Expected Outcome:

  • Glucose cannot move due to the membrane.
  • Water moves to balance concentration (from side B to side A).
  • Volume change on the sides due to water movement, but glucose remains constant.

Detailed Explanation

• Free Water Molecules:

  • Water not associating with solutes.
  • Solutes form hydrogen bonds with water, reducing free water.

• Concentration Gradient:

  • Water moves from high to low free water concentration.

Biological Importance

• Bacterial Cells:

  • Gram-Positive Bacteria:
    • Thick peptidoglycan layer.
    • Structural protection against osmotic stress.
  • Gram-Negative Bacteria:
    • Thin peptidoglycan layer + outer membrane.
    • Protection against chemical degradation (antibiotics, enzymes).

• Comparison of Bacteria:

  • Gram-positive: Stronger structural integrity.
  • Gram-negative: More resistant to chemicals.

Additional Terms (Not Covered in Detail)

• Hypotonic, Isotonic, Hypertonic Solutions:
  • Important for understanding clinical settings and literature.
  • Not covered for simplicity but essential to know.

Conclusion

• Osmosis is crucial for understanding cellular water regulation.
• The movement of water based on free molecule availability is vital for equilibrium.
• Bacterial adaptations demonstrate different evolutionary strategies for stress resistance.