Diffusion of Molecules

Principle(s) Illustrated

1.     Diffusion of molecules move from areas of high concentration to areas of low concentration.

2.     Transport of substances across cellular boundaries are regulated.

3.     Diffusion cannot be observed when a cell is in a state of balance and equilibrium.

4.     Particles must be smaller than membrane openings in order for diffusion to occur.

Standards

• 7.1   All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope.

• 7.1a.   Cells function similarly in all living organisms.

• 7.5   The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function.

• 7.5a.  Plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.

• 7.5b.   Organ systems function because of the contribution of individual organs, tissues, and cells. The failure of any part can affect the entire system.

• 7.6   Physical principles underlie biological structures and functions.

• 7   Scientific progress is made by asking meaningful questions and conducting careful investigations.

• 7c.   Communicate the logical connection among hypothesis, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence. (Diffusion lab)

•  7e.   Communicate the steps and results from an investigation in written reports and verbal presentations.

Prior Knowledge & Experience

• Record your responses into your science journal.

• What is diffusion?

• What do you know about how oxygen is taken into the body?

• What do you know about how cells get rid of waste?

• How do cells take in oxygen?

• How do mammals take in oxygen?

• How is the process of taking in oxygen similar to cells taking in oxygen for Homo sapiens?

• How do most mammals get rid of wastes?

• Homo sapiens excrete solid, liquid and gaseous waste products. How is the process of excretion similar in cells compared to the process of excretion in Homo sapiens?

Research

Diffusion of the various extracts diffuses through the membrane of the balloons. Balloons are made of a rubber latex polymer of long chain-like molecules, or strands, that are all snarled together with bonds between the strands, called cross-links. Cross-linked molecule networks can be stretched and penetrated. Since the balloons's membrane is thin, semipermeable and there is a higher concentration of vanilla molecules inside the balloon vanilla will diffuse through the balloon's membrane. The vanilla molecules are small enough to diffuse out of the balloon where there is little or no concentration of vanilla. The pores of the balloon's rubber is large enough that the gases given off by the vanilla extract can move through them.

In the human body, capillary walls are one cell thick. Capillaries are the location where oxygen and glucose are exchanged between the blood and the body's cells. Carbon dioxide and cellular waste travel in the opposite direction of oxygen and glucose. This exchange between the blood and body cells is called diffusion.

Rates or velocities (u) of diffusion and effusion of gases are inversely proportional to the square roots of their molecular or atomic weights (M). According to Graham's law it states that the lighter the gas, the faster it will effuse (or diffuse). Mathematically speaking rates can be determined as follows: Rate1/Rate2=square root of (Mass2/Mass1).

In your science journal define each language of the discipline vocabulary word. Create a "list" document with three columns. In the first column record the vocabulary word, in the second column write the definitions and in the third column draw an illustration that represents the vocabulary word. In lieu of drawing images you may use images from the internet or magazines.

Use the language of the discipline to write a story about how and what kind of substances diffuses through cell membranes.

Language of the Discipline

1. Diffusion

2. Cells

3. Excretion

4. Molecules

5. Semipermeable

6. Capillaries

7. Velocity

8. Graham's law

9. Effusion

Materials

• 3 Balloons

• 3 Pipettes

• One tablespoon

• One tablespoon of liquid vanilla extract

• One tablespoon of liquid almond extract

• One tablespoon of liquid anise extract

Procedures

• Measure out one tablespoon of vanilla.

• Pour tablespoon of liquid into balloon.

• Inflate balloon with air.

• Tie off balloon.

• Repeat procedure for the almond extract and another for the anise extract.

• Allow balloons to sit.

• Check balloons every two minutes.

• Record observations.

Root questions

• How do particles in diffusion move?

• How do vanilla particles move?

• How do various substances diffuse through cell membranes?

• What evidence is there that vanilla extract diffuses through the balloon's rubber membrane?

• What is the relationship between the surface area and the volume of the balloon?

Common Misconceptions

• A common misconception middle school student may have about this experiment is that since vanilla extract and other extracts are liquids they cannot diffuse through the rubber of the balloon.

• The vanilla cannot be detected.

• Students do not perceive that the balloon's rubber have pores, therefore the vanilla extract cannot diffuse through the rubber.

Movies

Diffusion Science Experiments

Food Coloring Diffusion

Osmosis Demo with Raw Egg

References

California State Science Standards

Thomas Graham's Law

Effusion