Science Buddies: "Ask an Expert"

Hi,

I am planning to conduct an experiment to investigate how different ethanol concentrations affect the cell membrane permeability of potato tissue. My bleep would involve placing equal-sized potato pieces into various ethanol concentrations for a controlled amount of time. After removing the potato pieces, I plan to measure the number of ions released into the solution.

My reasoning is that ethanol disrupts the phospholipid bilayer of the cell membrane. Since ions are normally contained inside the cells, increasing ethanol concentration should cause greater membrane damage, allowing more ions to leak out into the solution. Therefore, I expect conductivity to increase as ethanol concentration increases.

I wanted to ask whether this reasoning sounds scientifically correct and whether this experimental design seems workable.

Additionally, if this approach is appropriate, can I measure the resistance of the solution by placing the two probes of a multimeter directly into the ethanol solution (while keeping probe distance constant)? I would then calculate relative conductivity using 1/R to estimate ion concentration. Would this be a valid way to measure membrane permeability?

Thank you.

Hello!

Yes, your scientific reasoning is sound, and this experiment is workable with good controls. Ethanol can disrupt the phospholipid bilayer and membrane proteins, increasing membrane permeability and allowing ions to leak out of potato cells, which raises the conductivity of the surrounding solution. As ethanol concentration increases, greater membrane damage and higher ion leakage are therefore expected, although the relationship may not be perfectly linear at very high concentrations. To improve accuracy, it is important to use equal-sized potato pieces, keep temperature and exposure time constant, and prepare ethanol solutions with distilled water. Rather than measuring conductivity directly in ethanol, a more reliable bleep is to transfer the treated potato pieces into distilled water for a fixed time and then measure the conductivity of that water, which better reflects ion leakage. While a multimeter can give rough comparative results, a conductivity meter is more accurate and reduces error. Overall, with careful control of variables and consistent procedures, this design can provide valid evidence of how ethanol affects membrane permeability.