Principles of Physiology Membrane Permeability - Assignment Example

SLE211 ~ Principles of Physiology Membrane Permeability Worksheet - Instructions This is the first of 5 worksheets which you will complete for the practical component of SLE211 (Principles of Physiology). This worksheet will refresh your generic skills required for practical report writing – referencing, graph interpretation and scientific writing. This practical worksheet is worth 5% of your final mark for the unit. Individual marks for each section are shown. The questions are marked out of 30. Marks are given for “Professionalism” which includes referencing, spelling and grammar total 15. This worksheet is marked out of 45. A marking rubric is provided. This is the guide that the markers are going to use to mark your practical worksheets. Study it carefully. You need to print one of these sheets and include with your worksheet. Information in the Survival Skills folder on DSO will assist you with referencing and explain how to create a graph in Excel. Please read the instructions carefully. Answer all questions. Assessment Check Once you have completed the worksheet please submit your worksheet electronically to the Check your work – Practical Worksheet One in the Assessment Check folder. It may take 15-20 minutes to generate a report so please be patient. This report will tell you how similar (in a %) your work is to other published work. In the example below there is 82% similarity (unacceptable!). One the right hand side it lists where the information has come from listed under 1, 2 and 3. Ideally you should have 0% if you have referenced correctly and put the answers in your own words. Once you have the report if you have any hits (coloured text) which for this piece of work should total no more than 20% you will need to write a short justification for each hit that you receive on your worksheet. Alternatively you can re-write those sections and re: run the Turn It In Report. I understand that students like to include the instructions and or questions in their submission. If the highlighted text is part of the question or instructions for the worksheet then you do not need to justify. You only need to justify “hits” (highlighted text) that you receive on your answers. Diagrams from textbooks are acceptable but they must be referenced correctly. If you use the diagram exactly how it appears in the textbook the reference would be (Sherwood, 2010). If you add something to the diagram to aid in your explanation (preferable) then the reference would be (modified from Sherwood, 2010). If you have drawn your own original version of a diagram to explain then you will not need to reference (even better option). If you are getting lots of hits and it is showing a lot of similarity with already published work then you are not doing this correctly. You need to modify your style of writing (put it in your own words) and seek assistance with referencing and / or scientific writing. You cannot copy slabs of text from website or published documents (even if it is referenced) – this will come up as a hit. You need to put the information in your own words and then reference it. You can submit to Assessment Check multiple times to check your work. More information about Turn It In can be found at: http://www.deakin.edu.au/current-students/study-support/dso-support/turnitin/index.php Due Date: At your next practical class i.e. the week beginning March 26. Submission: You submit the worksheets to your demonstrator in the prac class. Aims of this worksheet (1) To gain an understanding of the permeability of plasma membrane of erythrocytes to various substances. (2) To create a graph using Excel (or other suitable graphing program). (3) To interpret information presented in graphs and figures. (4) To correctly use and cite references in your report. What do I submit? Please submit answers to all sections of the following questions for assessment. A copy of your Turn It In report (Assessment Check) with a justification for any highlighted text in your answers. Do not submit pages 1 and 2 of this instruction sheet. This document is an active Word document so you can type your answers directly into the document, and print it out for submission. Please keep a copy of this worksheet for your own records. This is good practice for all your units. You must attach an Assignment Attachment form (completed and signed) to your worksheet for submission (available in the lab) and include a copy of the marking rubric. SLE211 ~ Principles of Physiology Membrane Permeability Worksheet Check list – please tick I have completed all the questions in the worksheet I have proof read my answers and checked for spelling mistakes I have used the correct format for references in the reference list and the in-text citations All references in the reference list have been used as an in-text citation and vice-versa. The Turn It In Report is included with any justifications to highlighted text. I have completed and signed the assignment submission form and attached it to the worksheet. A copy of the marking rubric is attached. Part A – Plasma membrane and osmotic pressure of NaCl solutions Question 1 In the practical class we examined the classic demonstration of osmosis where red blood cells were immersed in solutions of varying osmolarity as shown in the representative pictures below. Figure 1 – The appearance of red blood cells after exposure to NaCl solutions of different concentration. (a) The number of cells in the solutions A and B are lower than the other solutions (C, D and E). Why? Solutions A and B are hypotonic to the intracellular fluid of the red blood cells immersed in them. This implies a higher concentration of the solute, sodium chloride in the solution as compared to that inside the cell cytoplasm. This led to a continuous inflow of water molecules into the cells making them to swell and haemolyses (process of haemolysis) (Carpenter, 2009, p. 76) The process involves bursting of the semipermeable cell membrane of the red cells. This led to the reduction in their numbers in the solution. In C, D, and E, the extracellular solutions are hypertonic to the intracellular fluids. This means that the concentrations of sodium chloride in the solutions are higher compared to that in the cytoplasm of the red blood cells (Practical Manual, p. 54). This makes the cells lose water through osmosis via the semipermeable membranes. The cells, therefore, maintain their original number depending on the concentration of the solutions. (2 marks (b) Describe the shape of the cells in the solution B and E and explain why they are this shape. The cells in B are swollen and are biconvex in shape while those in E are crenated and are biconcave in shape. Solution B is a hypotonic solution, therefore, water molecules move from the solution into the cell cytoplasm through the process of osmosis via the semipermeable cell membrane (Blum, 2006, p. 45). (2 marks) Question 2 Part B –Erythrocyte osmotic fragility test (a) Plot a graph of the results obtained for the Erythrocyte osmotic fragility test i.e. plot the degree of haemolysis of the red blood cells versus the osmolarity of the solutions The graph must be created using Excel or other suitable graphing program. Instructions for how to draw a graph and the major features of a graph are provided on DSO. The graph must have: An informative title and figure number Be an appropriate size (i.e. not the size of a postage stamp!) Correctly labelled axes with units Appropriate sized data points with line Arbitrary scale that is appropriate (6 marks) mOsm 0 102 136 170 206 240 274 308 343 376 410 Degree of Haemolysis 4 4 4 3 3 3 2 2 1 1 1` Graph of Osmolarity versus Degree of Haemolysis a). (b) Write a legend for this graph i.e. a written description of what has been plotted. (See example of a legend is shown in Figure 3) (4 marks) Osmolarity versus degree of haemolysis. Osmolarity was obtained through use of arbitrary scale in the assessment of the size of the pellets, and noting the supernatant color. + Sign represents the number of pellets that resulted from the haemolysis of the red blood cells. The two value types have close relations and are dependent on each other, thus, they can be plotted on a graph as shown above. The osmolarity is directly proportional to the degree of haemolysis. (c) Write a brief interpretation of the result in the graph i.e. what do the results presented in this graph tell you about osmolarity and red blood cells. Hint: You will need to relate the result you obtained to the theory you have learned in lectures. The degree of haemolysis represented by the number of red blood cells pellets is directly proportional to the osmotic pressure exerted by the intracellular fluid and the plasma on the cell membrane. This is because osmotic pressure reduces and hinders osmosis from taking place. When osmosis fails to take place across the membranes of the red blood cells, there is no continuous inflow of water molecules through the cell membrane; therefore, the cells do not haemolyse, thus the least number of pellets of red blood cells when the osmolarity is the lowest. The relationship between osmolarity and red blood cells is that osmolarity is necessary to keep the red blood cells in human or an animal’s body. (4 mark Part C – Permeability of the Plasma membrane Question 3 All the solutions used in this section were initially iso-osmotic. The table below states the approximate time taken for haemolysis of red blood cells in 4 of the solutions. (a) Explain the terms iso-osmotic and isotonic. (2 marks) Iso-osmotic refers to two solutions with the same osmolarity. Isotonic, on the other hand, refers to solutions with the same solute concentration. (b) For each of the iso-osmotic solutions shown in the table, explain why or why not these solutions are isotonic or hypotonic. Your explanations should include how different molecules cross the membrane. You can use diagrams to help with your explanations. Isotonic solutions are Sodium Chloride and Potassium Chloride. Haemolysis of the red blood cells takes the same time to occur in both solutions. This implies that they have the same osmotic pressure that hinders osmosis to take place. Osmotic pressure or osmolarity of a solution is determined by the solute concentration of the solution. It, therefore, follows that the two solutions have the same solute concentration, that is, they are isotonic. Hypotonic solution is urea. It takes the shortest time for the haemolysis of red blood cells to take place in urea compared to other solutions (Practical Manual, p. 65). The solution is hypotonic to that of the intracellular fluid in red blood cells. Water thus flows into the cytoplasm of the cells through the semipermeable membrane using the mechanism of osmosis. The flow is faster due to the existence of larger osmotic gradient between the extracellular and the intracellular solutions as compared to other solutions. (8 Part D – Rate of diffusion across the cell membrane. Below is a graph created from the data in Part D obtained from students who completed SLE211 in 2011 Figure 3 – Mean haemolysis time (sec) for three different alcohols versus their partition coefficients (blue), molecular weights (red) and number of OH groups (green). Mean haemolysis time was calculated from data from 33 student groups in the SLE211 practical class in 2011. The partition coefficient values have been multiplied by 104 and the number of hydroxyl groups by 100 so all values can be plotted on the one axis. The mean haemolysis times were all significantly different from each other (P Read More