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Bronxville Union Free School District

Seventh-Graders Test Selective Permeability of Dialysis Tubing

Seventh-graders, who have been learning about animal and plant cells and studying the basics of different cell parts, participated in a hands-on science lab experiment to further understand how molecules get diffused across the cell membrane.

Using dialysis tubing, a type of semipermeable membrane tubing used in separation techniques, the students modeled a cell membrane to investigate the selective permeability of dialysis tubing. To begin the experiment, they tied both ends of the dialysis tube to form a bag, which was filled with cornstarch. Then, they added water and several drops of iodine to a beaker and placed the bag into it. After that, the students observed whether the color of the solution in the bag would change, indicating that the iodine was able to pass through the membrane into the bag.

“The purpose of the lab was for the students to gain better science lab skills,” said science teacher Jennifer Zopp, who teaches the curriculum along with fellow teacher Karen Green. “It also allowed them to see that diffusion can happen across a membrane. Sometimes, not seeing something doesn’t mean it’s not actually there, which is a hard, abstract concept for middle school students to understand.”

Throughout the science experiment, the students took notes on their observations, wrote down the procedures and steps they took, created data tables and constructed a hypothesis. During their next science lab experiment, they will redesign the lab with slightly different materials and continue to make discoveries on their own.

“Some students often choose to work in the opposite direction, where they put iodine in the cell and cornstarch in the beaker solution to see if it’s a one-way passage or if it can go both ways,” Zopp said.  

The science lab experiment challenged and encouraged students to collaborate with their peers and think critically to solve a problem, skills closely aligned with the dispositions of the Bronxville Promise.

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  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image
  • Bronxville Union Free School District - Image