CAS BI 315 Lecture Notes - Lecture 5: Paracrine Signalling, Human Body, Oxytocin Receptor

Cell Membranes Lab Report

1. Diffusion

1. Compare the following terms: solvent, solute, andsolution.

2. Go to Lab, Section I, Exercise 1 to explore the factorsinfluencing the rate of diffusion and complete the following:

1. Predict how molecular mass and temperature may affect theoutcome of this experiment.

2. Record the data from information in the Lab in the tablebelow.

3. 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.

2. Osmosis

1. Go to Lab, Section II, Exercise 2 to view a demonstration ofosmosis and answer the following questions:

1. Describe the net movement of water in osmometer 1.

2. How is the movement of water molecules related to theconcentration gradient of the solution?

2. Go to Lab, Section II, Exercise 3 to observe the effect ofsolute concentration on the rate of osmosis. Answer the followingquestions:

1. Was the net movement of water in bags 1 to 4 into or out of thebags?

2. Explain the results from bags 4 and 5.

3. Selective Permeability of Membranes

1. Go to Lab, Section III, Exercise 4 to learn about theimportance of selectively permeable membranes, then complete thetable and answer the following questions:

1. Which substances diffused through the dialysis membrane?

2. How does dialysis tubing model the selective permeability of aplasma membrane?

4. Tonicity

1. 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.

2. 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.

Summary Questions

1. 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?

Dialysis bags or model “cells” (A, B, C and D) are placed in beakers containing a 20% sucrose solution. Each model “cell” contains an unknown concentration of sucrose solution. Every 15 minutes, the model “cells” are weighed and the data entered in the table below. Table: Mass of Model “Cells” Containing Different Concentrations of Sucrose Time (minutes) is 0,15,30,45. “Cell” containing solution A is 11.4, 11.3, 11.2,11.3(mass grams) “Cell” containing solution B is 12.5, 13, 13.5, 14(mass grams) “Cell” containing solution C is 10.8,9.6, 8.2, 7.2(mass grams) “Cell” containing solution D is 10.8, 10.2, 9.5, 9.2(mass grams) what is the Movement of Water, % Sucrose in “Cell” & Tonicity in “Cell” of each cell (A-D)

a) Use the data in the table to determine the movement of water. Choose from “Into the cell”, “Out of the cell” or “No net movement of water” Write your answer in the row of the table labeled “Movement of Water”.

b) Based on the movement of water, you can determine what the concentration each solution must have been at the beginning of the experiment for each model “cell” A-D. Choose from 40%, 20%, 15% or 10%. Write your answer in the row of the table labeled “% Sucrose in Cell”.

c) Determine whether each sucrose solution in the “cell” is “hypertonic”, “isotonic” or “hypotonic” relative to the solution outside the “cell”. Write your answer in the row of the table labeled “Tonicity in Cell”. Answer the questions below about Part II of this exercise:

1) A. Explain why was there little or no weight change for the model “cell” containing solution A?

B. This system is said to be at equilibrium. Explain what equilibrium means in terms of the movement of water across the plasma membrane of a cell?

2) The model “cell” containing solution B gained weight. Therefore, the water moved _________ the “cell”. Explain why the water moved as it did in this model system.

3) Model “cells” C and D both lost weight. Therefore, the water moved _________ the “cell”. Explain why the water moved as it did in these systems.

4) A. “Cell” C lost more weight than “cell” D over the same amount of time (60 min). Therefore, “cell” C lost water at a slower or faster rate than “cell” D. (circle one)

B. Explain the cause of the difference in the rate of water loss for “cell” C and D.

5) Do you see a pattern of how water flows into or out of the cell based on the concentration of solute?

Water always moves from a ______________tonic solution to a ____________tonic solution.

6) In the experiment your group will design, you will be using a piece of potato composed of many living cells. Based upon what you have learned about osmosis and tonicity, predict whether a potato core would gain weight, lose weight or stay about the same weight if you placed it in each of the following solutions: Hypertonic – Isotonic - Hypotonic –