Determination of Osmotic Potential of Red Onion

Introduction

The presence of solutes in water causes the osmotic potential to decrease and it reduces the free energy of water. This is because water molecules will tend to bind to the solutes rather than moving freely and away from the solution. If cells are surrounded by a solution that has an osmotic potential more negative (lower) than that inside the cell, water will move from inside the cell (higher water potential) to the outside solution (lower water potential) by osmosis. This water loss causes a decrease of the protoplast cell volume and eventually leads to plasmolysis (the separation of the plasma membrane from the cell wall). The objective of this exercise is to estimate the osmotic potential of the external solution that causes 50% plasmolysis in red onion epidermal cells.

Materials and Methods: Epidermal sections of red onion were placed in a series of sucrose solutions of increasing sucrose concentration. After a treatment period...