Tonicity The relative concentration of solutions Hypertonic Isotonic

Tonicity: The relative concentration of solutions. Hypertonic, Isotonic and Hypotonic.

What is a solution? • There are two components or parts to a solution. • The first part of the solution is called the solvent which is often a liquid. • In most biological systems (like you and me) the solution is water. • In fact, water is called the universal solvent.

What is a solution? • The second part of the solution is called the solute. • This can be a gas, liquid or solid. • The solute is dissolved in the solvent. • Salt (Na. Cl), and starch are all examples of solutes.

Effect of solution on osmosis. • Osmosis is the term used to describe the movement (diffusion) of water molecules across a cell membrane. • The water moves from areas of high concentration to areas of low concentration.

Types of solutions • To determine the type of solution you cell is in, you compare it to the concentration of the solution within the cell. • If the concentration of solution outside the cell is higher than inside the cell it is called a hypertonic solution. • If the concentration of solution outside the cell is the same as inside the cell it is called an isotonic solution. • If the concentration of solution outside the cell is lower than inside the cell it is called a hypotonic solution.

Hypertonic solution • What happens to a cell when it is placed in a hypertonic solution? • If the cytoplasm of a cell is 95% water and 5% Na. Cl and it is placed in a solution that is 90% and 10% water, what would happen? • Will water move into the cell, or will the water move outside the cell?

Isotonic solution • When a cell is placed in a solution that has the same concentration as the cytoplasm what will happen? • In which direction will osmosis occur?

Hypotonic solution • What would happen to a cell placed in a hypotonic solution? • Consider a case where a cell with 95% water and 5% salt was placed in distilled water (100% water). • What would happen to this cell?

Results

Summary • When a cell is placed in a hypertonic solution, water diffuses out of the cell, and it shrivels up. In plant cells, you can see the cell membrane pull away from the cell wall. • In an isotonic solution, the cell remains the same. The rate of osmosis is the same in both directions. This is equilibrium.

Summary continued. • When a cell is placed in a hypotonic solution water diffuses into the cell and causes it to expand, and then burst (lyse). • The cell wall in plants prevents it from bursting. This contidion is called turgidity.

Effect of tonicity • These are red blood cells. Isotonic Hypertonic Hypotonic

Tonicity and plant cells Hypertonic Hypotonic

What happens to a salted slug?