Diffusion (Tara Alton)

Author

Tara Alton

Principle(s) Illustrated

1. Diffusion/ passive transport

2. Semipermeable membranes

3. Molecules move from high concentration to low concentration (concentration gradients)

4. Hypertonic, hypotonic and isotonic solutions

Standards

• 1.a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings

Questioning Script

Prior knowledge & experience:

Students already know that iodine is a starch indicator.

Root question:

Why did the contents of the baggie change color?

What can pass through the membrane? What does not pass th

rough the membrane?

Iodine solution: is the baggie or the beaker hypertonic?

Starch solution: is the baggie or the beaker hypertonic?

Target response:

Only the iodine passed through the membrane (baggie) from high to low concentration. The iodine reacts with the starch in the baggie and turns a purplish color.

Common Misconceptions:

Becuase the baggie is impermeable to water, it must be impermeable to anything else.

Photographs and Movies

References

Diffusion Lab Key