Osmosis of Water

Biology 105 Lab

3/22/11

Introduction

Cells have kinetic energy, a source of energy stored in cells. This energy causes molecules to bump into each other and move in new directions. Diffusion is one result of this molecular movement. Diffusion is the random movement of molecules from an area of higher concentration to areas of lower concentration. Osmosis is a special kind of diffusion where water moves through a selectively permeable membrane that only allows certain molecules to diffuse though (Lab Manual 7e, 2010).

Diffusion or osmosis occurs until dynamic equilibrium has been reached. This is the point where the concentrations in both areas are equal and no net movement will occur from one area to another. If two solutions have the same solute concentration, the solutions are said to be isotonic. If the solutions differ in concentration, the area with the higher solute concentration is hypertonic and the area with the lower solute concentration is hypotonic.

Besides osmosis and diffusion, molecules and ions can be moved by active transport. This process includes the use of ATP (adenosine tri-phosphate) to drive molecules in or out of a cell. Active transport is generally used to move molecules against a concentration gradient, from an area of low concentration to an area of higher concentration of molecules. The purpose of this experiment was to show that osmosis of water thru plant stomata does not require energy (ATP).

Materials and methods:

In order to test the hypothesis, epidermis from the Zebrina plant was removed with a razor into 4 pieces and was placed in Petri dishes. Tweezers were then used to place each epidermis onto one of four slides. Each of the four slides contained different solutions: Distilled Water, Sucrose, DNP, and Sucrose plus DNP. Cover slips were then used to place