The plasma membrane acts as a barrier in cells of all types to control the movement of substances into and out of the cell.a) Explain how the plasma membrane acts as a semi-permeable barrier to various types of molecules based on its molecular structure.b) Describe, in detail, three ways in which proteins can cross the plasma membrane.NOTE: A complete answer will require some information from earlier in the course, especially the information on plasma membranes in the Prokaryotes topic.
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Cell Membranes Lab Report
- Diffusion
- Compare the following terms: solvent, solute, andsolution.
- Go to Lab, Section I, Exercise 1 to explore the factorsinfluencing the rate of diffusion and complete the following:
- Predict how molecular mass and temperature may affect theoutcome of this experiment.
- Record the data from information in the Lab in the tablebelow.
| Time (min) | Diameter (mm) | |||
5°C MB | 5°C PP | 23°CMB | 23°C PP | |
0 | ||||
15 | ||||
30 | ||||
45 | ||||
- Construct a line graph of the data from the table above. Yourgraph should include labeled axes, units, and a legend indicatingwhich treatment is presented. Sign, date and prepare an image ofyour graph and include it with this lab report.
- Osmosis
- Go to Lab, Section II, Exercise 2 to view a demonstration ofosmosis and answer the following questions:
- Describe the net movement of water in osmometer 1.
- How is the movement of water molecules related to theconcentration gradient of the solution?
- Go to Lab, Section II, Exercise 3 to observe the effect ofsolute concentration on the rate of osmosis. Answer the followingquestions:
- Was the net movement of water in bags 1 to 4 into or out of thebags?
- Explain the results from bags 4 and 5.
- Selective Permeability of Membranes
- Go to Lab, Section III, Exercise 4 to learn about theimportance of selectively permeable membranes, then complete thetable and answer the following questions:
Contents of Beaker | ||
0 Min | 30 Min | |
Starch | ||
Chloride ion | ||
- Which substances diffused through the dialysis membrane?
- How does dialysis tubing model the selective permeability of aplasma membrane?
- Tonicity
- Go to Lab, Section IV, Exercise 5 and 6 to observe plasmolysisin Elodea cells and tonicity in red blood cells. Summarizethe concept of tonicity using blood and Elodea cells asexamples. Your description should incorporate these terms: turgid,plasmolysis, hemolysis, and crenation.
Cells | Isotonic Solution | Hypertonic Solution | Hypotonic Solution |
Elodea | |||
RBC |
- Based on your previous work, reproduce the table below and drawan illustration of a single cell in each box. Include arrows toshow the direction of water flow relative to each cell and dots tosymbolize solutes. Sign, date and prepare an image of your drawingand include it with this lab report.
Cells | Isotonic Solution | Hypertonic Solution | Hypotonic Solution |
Elodea | |||
RBC |
Summary Questions
- Compare diffusion and osmosis. Give an example of each.
2. In which direction will osmosisoccur if a 15% sugar solution is separated from a 25% sugarsolution by a selectively permeable membrane?
3. Why did osmosis, but not diffusionof sucrose molecules, occur across the dialysis membrane containing20% sucrose solution?
4. You are having a party and thecelery is limp. What might you do to make the celery crisp (turgid)again? What will occur in the cells?
5. A small amount of fertilizer(mineral salts) will stimulate plant growth, but over fertilizationcan kill plants? Why?
6. Michael adds sugar to his coffee.Explain what in this drink is the solvent, solute, and solution.
7. You add a cube of sugar to yourdrink. How could you speed up the diffusion of sugar moleculeswithout stirring?
8. How is dynamic equilibriumestablished within a solution?
