Vernier Software & Technology

# Diffusion

## Introduction

Diffusion is a process that allows ions or molecules to move from where they are more concentrated to where they are less concentrated. This process accounts for the movement of many small molecules across a cell membrane. Diffusion is one of the processes by which cells acquire food and exchange waste products. Oxygen, for instance, might diffuse in pond water for use by fish and other aquatic animals. When animals use oxygen, more oxygen will diffuse to replace it from the neighboring environment. Waste products released by aquatic animals are diluted by diffusion and dispersed throughout a pond.

One way to measure the rate of diffusion of ions is to monitor their concentration in solution over a period of time. Since ions are electrically charged, aqueous solutions containing ions will conduct electricity. A Conductivity Probe is capable of monitoring ions in solution. This probe however, will not measure the amount of electrically neutral molecules dissolved in water. Salts, such as sodium chloride, produce ions when they dissolve in water. An equation for the dissociation of sodium chloride in water can be written as follows:

If you place a salt solution in a container such as dialysis tubing, the salt can travel through the very small holes in the tubing. When dialysis tubing containing a solution of salt ions is placed into a beaker of water, the ions can diffuse out of the tubing and into the surrounding water. In this way, you will be able to measure the diffusion of salts in a solution of water and determine how concentration gradients and the presence of other particles affect the diffusion of the salt across a membrane.

## Objectives

After completing the Preliminary Activity, you will first use reference sources to find out more about diffusion and diffusion through a membrane before you choose and investigate a researchable question dealing with diffusion rate. Some topics to consider in your reference search are:

• diffusion
• facilitated diffusion
• salts
• ion channels
• ions
• dialysis
• semipermeable membrane
• active transport

## Sensors and Equipment

This investigation features the following Vernier sensors and equipment.

### Option 2

You may also need an interface and software for data collection. What do I need for data collection?

## Investigating Biology through Inquiry

See other experiments from the lab book.

 1 Buffer Investigations 2 Diffusion 3 Investigating Osmosis 4 Chemistry of Membranes 5 Investigating Protein 6A Testing Catalase Activity (O2 Gas Sensor) 6B Testing Catalase Activity (Gas Pressure) 6C Testing Enzyme Activity (Spectrometer) 7 Introduction to Biofuels: Enzyme Action 8 Analysis of Enzymes using Tyrosinase 9 Cellular Respiration 10A Sugar Metabolism with Yeast (Carbon Dioxide Gas) 10B Sugar Metabolism with Yeast (Ethanol) 11 Fermentation with Yeast 12 Photosynthesis by Chloroplasts 13 Transpiration of Plants 14 Plant Pigments 15 Heart Rate 16 Investigating Dissolved Oxygen 17 Investigating Primary Productivity 18 Modeling Population Dynamics 19 Water Monitoring 20 Evolution of Cellobiase in Fungi 21 Introduction to Molecular Evolution 22 Evolution of Yeast

### Investigation 2 from Investigating Biology through Inquiry Lab Book

#### Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.