Biology Forums - Study Force

Dialysis tubing is a cellulose material used to make model cells for experiments in osmosis and diffusion. These model cells do not use living cell membranes. A student made a model cell by pouring distilled water into some dialysis tubing. The student placed the model cell in a salt solution and waited 10 minutes. The cell was then removed from the salt solution and the contents poured into the test tube. The student added silver nitrate to the test tube and a white precipitate formed. This indicated that chloride ions had entered the cell. Would this be true for living cell membranes? Design an experiment to test this.

Yes, chloride ions can pass through the cell membrane of human cells. The cell membrane is selectively permeable, meaning that it allows certain ions and molecules to pass through while keeping others out. Chloride ions can pass through the cell membrane through ion channels or transporters, depending on the concentration gradient and the electrochemical gradient. A simple experiment would require the isolation of cells, such as red blood cells. One group of cells would be submerged in a known concentration of salt, the other without (control group). After 20 minutes, the cells would be collected, washed from any excess salt water, blended so that cell membrane is disrupted, and subsequently exposed to silver nitrate. If the precipitate forms in the experimental group, it suggests that the cells are permeable to chloride, and so a transport mechanism exists. It is also important that no precipitate forms in the control group.

Hope that helps