Membranes: Cell Membrane and Purple Dark
Cell Membranes and Transport Hands-On Labs, Inc. Version 42-0033-00-01 Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor. Exercise 1: Diffusion Observations
The results of this lab were greatly influenced by the temperature of the KI solution. The bag placed in the heated solution began to change color (from white to light purple) almost immediately and changed to dark purple within 7minutes. The second bag in room temp. solution took about 5 minutes to see a slight change in color (from white to light blue) and about 20 to turn dark purple. The third bag in the cold temp. solution barely changed color at all at the end of the hour (bluish tint. ) According to the text (p. 68), “ Because the driving force for diffusion is the kinetic energy of the olecules themselves. The speed of diffusion is influenced by molecular size ( the smaller, the faster) and by temperature ( the warmer, the faster). ” Through this lab experiment we were able to see that diffusion did happen faster in the warm water by seeing the fastest change in color of the contents inside the baggie. B. Did the sizes of the molecules affect their movement? Yes, the smaller the molecules (KI) were able to permeate thru the bag where as the bigger molecules (water) and corn start could not permeate thru the membrane bag due to their large size. C.
Give an example of diffusion between: a solid and a liquid; a gas and a liquid; between two different solids. (solid/solid) Gold and lead- over time, molecules of lead will diffuse into the gold and vice versa. (solid/liquid) Sugar and water- Sugar will dissolve in water. (Gas/liquid)Perfume and air- the scent will spread. Exercise 2: Osmosis Observations
Questions A. Describe how the potato cylinders changed in their turgidity. Identify which of the solutions were isotonic, hypertonic, and hypotonic in relation to the potato. Hypertonic solution. No change in turgidity. Hypotonic solution. What would happen to a red blood cell placed in distilled water? Why? Distilled water is a hypotonic solution which means in contains no solutes. According to the text (p. 72), “Cells placed in a hypotonic solution plump up rapidly as water rushes into them. ” This means that a RBC would eventually pop.
Create a graph of your experimental data by plotting the percent change in potato mass against sucrose molarity. Label the x-axis as “Molarity of Sucrose,” and the y-axis as “% Change in Mass. ” Determine the molar concentration of the sucrose contained in the potato strips by using the graph created in question C. At the point where the molar concentration of the sucrose in the potato would be isotonic to the sucrose, there would be no net change in the potato mass. On the graph, this is located at the 0% change. Draw a line from this place on the y-axis to intersect the line.
From the line draw a line down to the x-axis to find the molarity. Molar concentration of sucrose in potato = . 3 M Exercise 3: The Effect of Solvents on Membrane System Observations Data Table 3: Color Intensity from Damaged Beet Cells
Questions A. What is the reasoning behind the use of egg whites?
How does this part of the experiment relate to membranes? Egg whites would provide a lipid layer mimicking the cell membrane layer of a cell. Also egg white are largely composed of water this would also mimic the cell membrane. B. What do the results of test tube e tell about the effect of isopropyl alcohol on egg whites? The effects of the alcohol on the on the egg whites were that it made the chunky as almost if they had been cooked. C. What do the results of test tube f tell about the effect of isopropyl alcohol on oil?
How does this relate to membranes? The oil sinks in relation to the alcohol. This is related to membranes due to the hydrophilic and hydrophobic aspects. Lipids arrange so that the hydrophobic “tail” regions are isolated from the surrounding polar fluid, causing the more hydrophilic “head” regions to associate with the intracellular (cytosolic) and extracellular faces of the resulting bilayer. D. Based on the results from test tubes a through d, which of the solutions caused the most damage on the membrane system? Explain your answer.
The solution with the highest concentration of Isopropyl alcohol cause the most damage to the membrane because exposure to high concentration of organic solvents would disrupt membrane integrity. E. Using the same data collection method, develop a hypothesis and use the scientific method to design an experiment that would show the effect of temperature stress on membranes. Extreme temperatures, mainly -5? C and 70? C, will significantly damage the cell membrane while the temperatures closer to room temperature will cause only slight damage, if any.