Lecture: Hypotonic vs. Hypertonic Solutions

Introduction to Solutions

• Definition: A solution is a mixture where one substance dissolves in another.
  • Solute: The substance that is dissolved (e.g., sugar).
  • Solvent: The substance that causes the solute to dissolve (e.g., water in biological solutions).

Cell Membrane and Semi-Permeability

• Cell Membrane: Composed of a phospholipid bilayer, it is semi-permeable.
  • Allows certain molecules to pass freely (e.g., water).
  • Restricts others, often due to size or charge (e.g., solutes).

Osmosis

• Definition: Movement of water from areas of high concentration to low concentration through a semi-permeable membrane.

Hypotonic Solutions

• Definition: Solutions with a lower concentration of solutes.
• Example: Beaker with 80% water, 20% solute compared to a cell with 60% water, 40% solute.
  • Hypotonic solution is the one in the beaker (20% solute).
• Effect on Cells: When a cell is placed in a hypotonic solution, water enters the cell, potentially causing it to swell and burst.

Hypertonic Solutions

• Definition: Solutions with a greater concentration of solutes.
• Example: Beaker with 50% water, 50% solute compared to a cell with 60% water, 40% solute.
  • Hypertonic solution is the one in the beaker (50% solute).
• Effect on Cells: When a cell is placed in a hypertonic solution, water exits the cell, causing it to shrivel.

Isotonic Solutions

• Definition: When equilibrium is reached with equal concentrations of solute and solvent on both sides of the membrane.
• Example: After osmosis, both sides have 67% water and 33% solute, creating an isotonic environment.

Conclusion

• Key Terms: Hypotonic, hypertonic, isotonic solutions and their effects on cell dynamics.
• Class Activity: Students are encouraged to pause the video and answer questions to reinforce their understanding.

This summary is intended as a study guide for students to understand the differences between hypotonic, hypertonic, and isotonic solutions and their impact on cells.