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Biology Membrane Lab

Introduction: In this lab i used glucose and starch to show if the cell membrane is permeable, impermeable, or selectively permeable to these substances. Dialysis tubing is a plastic like substance that has small pores in it. These pores allow certain chemicals to flow into and out of the cells. The size of the molecule determines what goes through the tubing. On of the materials that we will be using is glucose. glucose is a simple sugar that easily dissolves in water. To test for the presence of glucose we will use glucose test strips.

The strip will change from an aqua blue color to a brown color if there is glucose in the solution. Starch is a complex molecule that forms from a suspension in the water. To test for the presence of starch I will use Lugol’s iodin. When it comes in contact with the water and turns black or blue thats how you know that starch is present. Hypothesis: We tested the cell membrane to see if it was permeable or impermeable to glucose, and starch. I predicted that The cell membrane will be impermeable to starch.

It would be impermeable to starch ecause the dialysis tubing has small pores but the starch molecules are too big to fit through. The cell membrane will be permeable to glucose because the glucose molecules are are smaller than the pores in the dialysis tubing. Methods and Materials: The materials that we used are 2 cups, 2 pieces of dialysis tubing, water, glucose, glucose test strips, scales, lugols iodine, and a pipette. We tied one end of the glucose tubing, and put 2 inches of glucose solution into it then we tied the other side into a knot to close it up.

With the second dialysis tube we did the same thing ut with the starch solution. We then weighed the glucose cell, then the starch cell, and recorded the mass into the chart. After that we placed each cell into a seperate cup, and filled it with water. We let the cells sit in the cups overnight. The next day we got our cup with the glucose cell, we took a glucose test strip and dipped it into the water in the cup to test for glucose. Then we took the cell out of the water, weighed it, and recorded it in the chart. We took the cup with the starch cell and tested it for starch by using lugols iodine.

We put 4 drops of the iodine into the cup. We took the starch cell and weighed it, then recorded it. Mass of Glucose and Starch Results: When I got my cups i got the glucose test strips and the iodine to test for the substances of starch and glucose. When we tested the glucose cell with the test strip it chaged to a brownish color. This means that glucose was present. When we put iodine into the cup that had the starch cell in it it didnt change toa black color, so this means that starch wasn’t present. We then cut open the starch cell and the water turned black, and that showed us that starch was present.

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