Dialysis and Cells In this activity, you will use a membrane to construct your own cell model so that you can change both the internal and external environments. All of our experiments up to this have only allowed us to manipulate the external environment. You will use dialysis tubing and several solutions to build your cell model. You will have indicators, chemicals that show the presence of certain chemicals, to help in detecting what substances can and cannot pass through your membrane. Challenge: Develop an explanation for how boundaries and compartments help living systems maintain and regulate the conditions necessary for life. Constraints: Your design must: Be safe. Use dialysis tubing. Use starch suspension. Use glucose solution. Use appropriate indicators. Process 1. 2. 3. 4. 5. 6. 7. 8. 1 Brainstorm testable questions about how membranes affect internal environment of the cell. Each member of your group must come up with at least one original question. With your group, choose the testable question that you would like to question that you would like to investigate. Have your teacher approve your question. Design an experiment to test the question you chose. Have the teacher check and approve your design. Create a data table to record a brief summary of your experimental design and your predictions. Predict what will happen when you conduct the experiment, and record this information in the data table. Create a data table to record your observations and results on lab day. Have the teacher check and approve your design. NEED TO KNOW Background Information Dialysis tubing is a synthetic membrane, made of a thin, cellophane-like material. Microscopic pores in dialysis tubing allow molecules smaller than a certain size to pass through the membrane. Glucose is a simple sugar that dissolves readily in water. Glucose test strips indicate the presence of glucose in solution by changing color. Lugol’s iodine solution is an indicator that changes color in the presence of starch. Use one drop of Lugol’s iodine solution for every 1 mL of starch suspension: a blue black color indicates the presence of starch. Starch is a complex molecule that forms a suspension in water. Starch turns blue black in the presence of Lugol’s iodine solution. The size of a molecule is an important characteristic that partially determines how the molecules how the molecule behaves. Chemists have shown that all the molecules of different substances can vary significantly in size. Lab day: WEAR YOUR SAFETY GOGGLES!!!! 1. Set up and conduct your experiment. 2. Be sure to follow all the appropriate protocol for preparing your cell model for testing. 3. Wash your hands thoroughly. Analysis Make a lab report about your experiment. Include the following: 2 A statement of the question you tested and the results you predicted. A description of your methods, including the materials that you used A description of the results that you obtained, presented in a well-organized table or diagram An explanation of your experimental results that clearly explains how a cell membrane behaves as a barrier and how the dialysis tubing setup serves as a model of a cell. Protocol for Making a Cell Model For your cell model to work, the membrane must be the only barrier between the internal and external environment. Rinse all lab equipment with water, and handle the internal and external solutions for your experiment carefully to reduce the chance of contamination. Obtain a section of dialysis tubing; tie one end of the tubing securely so that nothing can leak out of the knot. Measure and record the amount of solution you will add to each cell model in your investigation. After carefully pouring the internal solution into your cell, tie the open end securely to prevent all leaking. Rinse the outside of your cell model to be certain there is no internal solution present to contaminate the external environment. Blot the cell model dry with a paper towel, and record its initial mass. After conducting your experiment, rinse, dry and record the cell model’s final mass.