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Diffusion through Membranes

Figure from experiment 1A from Advanced Biology with Vernier

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 the process 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 the pond.

It is important to consider how the rate of diffusion of particles might be affected or altered.

  • Diffusion may be affected by the steepness of the concentration gradient (the difference between the number of ions or molecules in one region of a substance and that in an adjoining region).
  • Diffusion might be affected by other different, neighboring particles. For instance, if oxygen diffuses towards a single-celled pond organism at a certain rate, will that rate be altered if some other molecule suddenly surrounded the organism?

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, water 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. 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

In this experiment, you will

  • Use a Conductivity Probe to measure the ionic concentration of various solutions.
  • Study the effect of concentration gradients on the rate of diffusion.
  • Determine if the diffusion rate for a molecule is affected by the presence of a second molecule.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Option 1

Option 2

Additional Requirements

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

Standards Correlations

See all standards correlations for Advanced Biology with Vernier »

Advanced Biology with Vernier

See other experiments from the lab book.

1ADiffusion through Membranes
1BOsmosis
2AEnzyme Action: Testing Catalase Activity
2BEnzyme Action: Testing Catalase Activity
3Mitosis & Meiosis
4APlant Pigment Chromatography
4BPhotosynthesis
5ACell Respiration (CO2 and O2)
5BCell Respiration (CO2)
5CCell Respiration (O2)
5DCell Respiration (Pressure)
6ApGLO™ Bacterial Transformation
6BAnalysis of Precut Lambda DNA
6BForensic DNA Fingerprinting
7Genetics of Drosophila
8Population Genetics and Evolution
9Transpiration
10ABlood Pressure as a Vital Sign
10BHeart Rate and Physical Fitness
11Animal Behavior
12ADissolved Oxygen in Water
12BPrimary Productivity
13The Visible Spectra of Plant Pigments
14Determination of Chlorophyll in Olive Oil
15Enzyme Analysis using Tyrosinase
16Introduction to Neurotransmitters using AChE
17Macromolecules: Experiments with Protein

Experiment 1A from Advanced Biology with Vernier Lab Book

<i>Advanced Biology with Vernier</i> book cover

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.

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Dev Reference: VST0040

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