AC

Diffusion and Osmosis Study Notes

Laboratory Objectives

  • Describe diffusion mechanism at the molecular level.

  • Identify factors influencing diffusion rates.

  • Explain role of selectively permeable membranes in osmosis.

  • Define hypotonic, hypertonic, and isotonic conditions.

  • Discuss cell wall influence on osmotic behavior.

  • Measure osmolarity using sucrose dilution in plant tissues.

  • Understand importance of diffusion and osmosis in cells.

  • Apply osmotic principles to various activities.

  • Engage in scientific processes including hypothesis formulation.

  • Develop communication skills through graph interpretation.

Introduction

  • Steady state in cells is maintained by regulated material movement through membranes.

  • Cytoplasm and extracellular environments are aqueous solutions (water and solutes).

  • Selective permeability of membranes allows water passage; regulates solute movement.

  • Active transport requires ATP, while passive transport occurs via diffusion.

  • Diffusion: Movement from high concentration to low concentration due to kinetic energy.

Osmosis

  • Osmosis: Diffusion of water across a selectively permeable membrane.

  • Occurs due to concentration differences of solutes that can’t pass through the membrane.

  • Water moves from areas of higher water concentration (lower solute) to lower water concentration (higher solute) until equilibrium.

  • Tonicity:

    • Hypertonic: Higher solute concentration than another solution.

    • Hypotonic: Lower solute concentration than another solution.

    • Isotonic: Equal solute concentration.

Experimental Exercises

Exercise 1: Diffusion of Molecules

Experiment A: Kinetic Energy

  • Observe molecular motion (Brownian movement)

  • Factors include size and random directionality of movement.

Experiment B: Selective Permeability with Dialysis Tubing

  • Test permeability of glucose, starch, and iodine potassium iodide.

  • Look for color changes as indicators of molecular presence.

Exercise 2: Osmotic Activity in Cells

  • Investigate osmotic behavior in plant (e.g., Elodea) and animal cells (e.g., red blood cells) under varying solutions:

    • Hypotonic: Cells swell and may burst (lysis).

    • Hypertonic: Cells shrink (crenation in red blood cells).

    • Isotonic: Normal state.

Exercise 3: Estimating Osmolarity of Plant Cells

Experiment A: Weight Change

  • Use potato cylinders in sucrose solutions to find at which molarity the weight remains constant (indicative of osmolarity).

Experiment B: Volume Change

  • Measure dimensions of potato cylinders to calculate volume and how it changes in different sucrose solutions.

Reviewing Knowledge

  • Key terms include selectively permeable, solvent, solute, diffusion, osmosis, hypotonic, hypertonic, isotonic, turgor pressure, osmolarity.

  • Compare osmotic responses of plant and animal cells.

Applications of Knowledge

  • Discuss implications of osmosis in food preservation and hydration systems.

  • Explore cell adaptations for osmoregulation in various organisms.

Investigative Extensions

  • Design experiments to explore the effects of salinity on marine organisms or to estimate osmolarity of cell structures, such as chicken eggs.