Overview
This lecture explains osmosis, tonicity, and their effects on cells, including demonstrations using dialysis tubing to illustrate hypotonic, hypertonic, and isotonic solutions.
Osmosis and Semi-Permeable Membranes
- Osmosis is the movement of water molecules across a semi-permeable membrane from higher to lower water concentration.
- Semi-permeable membranes, like those in red blood cells, allow water movement but restrict certain solutes.
Tonicity and Its Classifications
- Tonicity measures the osmotic pressure between two solutions separated by a semi-permeable membrane.
- Tonicity is determined by solutes that cannot pass through the membrane, such as sugar.
- There are three types of tonicity: hypotonic, hypertonic, and isotonic.
Hypotonic Solutions
- In hypotonic solutions, solute concentration is higher inside the cell than outside, causing water to enter the cell.
- Excess water entry can cause the cell to swell and possibly rupture (lysis).
- Demonstration: Dialysis tubing filled with sugar solution gains weight after being placed in water due to water influx.
Hypertonic Solutions
- In hypertonic solutions, solute concentration is higher outside the cell, causing water to leave the cell.
- Water loss results in cell shrinkage, known as crenation.
- Demonstration: Dialysis tubing filled with water loses weight after being placed in concentrated sugar solution due to water loss.
Isotonic Solutions
- In isotonic solutions, solute concentrations inside and outside the cell are equal.
- Water moves in and out at equal rates, so cell size remains stable.
- Demonstration: Dialysis tubing filled with water shows no weight change when placed in water.
Key Terms & Definitions
- Osmosis — Movement of water across a semi-permeable membrane from high to low concentration.
- Semi-permeable membrane — A barrier that allows certain molecules (like water) to pass but blocks others.
- Tonicity — The measure of osmotic pressure between two solutions, influenced by non-permeable solutes.
- Hypotonic — Solution with lower solute concentration outside the cell, leading to water entering the cell.
- Hypertonic — Solution with higher solute concentration outside the cell, leading to water leaving the cell.
- Isotonic — Solution with equal solute concentration inside and outside the cell.
- Crenate — The shrinking of a cell due to water loss.
- Lysis — The rupture or bursting of a cell due to excess water intake.
Action Items / Next Steps
- Review key definitions and effects of each tonicity type on cells.
- Prepare for possible lab activity demonstrating osmosis and tonicity using dialysis tubing.