Diffusion (Tara Alton)
Author
Tara Alton
Principle(s) Illustrated
Diffusion/ passive transport
Semipermeable membranes
Molecules move from high concentration to low concentration (concentration gradients)
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