Lab: Diffusion through Membranes
Background: Salt is a substance that is small enough to diffuse through cell membranes.
The diffusion of a substance through membranes is called passive transport. In this
experiment, you will test how different concentrations (the concentration gradient) of salt
solutions affects that rate of diffusion through a membrane. You will prepare solutions
of varying salt concentrations and place them in dialysis tubing submerged in a beaker
full of distilled water. The dialysis tubing will simulate a selectively permeable cell
membrane, and the distilled water will simulate the environment for a cell. Dissolved salt
in a solution can’t be observed first hand, but changes in the conductivity can be
measured. Therefore, in order to measure the amount of salt diffusing through the
membrane, you will measure the changes in conductivity in the water. The units that
measure conductivity are microsiemens (s) and you will covert that data to milligrams /
liter / second (mg / L / s) to measure the rate of diffusion. You will be comparing the rate
of diffusion in salt solutions of the following concentrations: 1% salt solution, 5% salt
solution, 10% salt solution.
Assignment: You will conduct this experiment, and complete a full lab report. Begin by
completing the experimental design diagram and preparing blank data tables in your lab
Creating Experimental Design Diagrams (review):
Begin by drawing a rectangle.
Write the independent variable across the top of the rectangle.
Divide the rectangle into labeled columns to represent the different levels of the
Identify your control.
Indicate the number of trials in each column.
Write the dependent variable beneath the rectangle.
List the constants beneath the rectangle.
Independent variable (IV):
Levels of Independent variable:
Dependent variable (DV):
Number of trials:
Design diagram (below):