Cell Membranes Lab Report

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The lab report is unique each semester and checks have been put into place to ensure students are doing their own work. Copying from other students or from outside sources will result in a zero on the accompanying lab quiz.

I. Diffusion

1. Highlight the following situations that will increase the rate of diffusion.
Variable Solution Solution
Molecular size Large (carbohydrates,proteins) Small (gases, ions)
Temperature Cold Warm or hot
Concentration gradient on either side of membrane Large concentration gradient Small concentration gradient

2. You make a smoothie with milk, banana,and protein powder. Identify each part of this drink.
solution:
solvent:
solutes:

3. In Ex 1 you explored factors influencing the rate of diffusion.
Potassium Permanganate (PP) =158 g/mole, Methylene blue (MB) = 320 g/mole
a. Record the data collected in the table below.
Time
(min) Diameter (mm)
5C MB 5C PP 23C MB 23C PP
0
15
30
45

b. The two variables being tested that speed diffusion are:

c. Looking at the above date which sample showed the least diffusion after 45 minutes? Why?

II. Osmosis

1. In Ex 3, determine the effect of solute concentration on the rate of osmosis. Complete the following table (a) and answer questions b – f below.

a. Examine the data collected in the lab and record the mass of each. Then subtract the initial mass from the mass of each of the five bags at 20 minutes and 40 minutes to determine mass change.

Bag Bag contents/ beaker contents Initial
Mass
0 Min
in g Mass
at
20 Min
in g Mass
at
40 Min
in g
Mass change 0 min Mass
Change
20 Min Total Mass
Change
40 Min
1 Distilled water/
distilled water
0 0 0
2 10% sucrose/
distilled water
0 +1.4
3 20% sucrose/
distilled water
0 +2.7
4 40% sucrose/
distilled water
0 +5.5
5 Distilled water/
40% sucrose
0 -3.7

b. Which bag lost mass?

c. Looking at the above data, which bags gained mass?

d. Which bag stayed the same?

e. Which bags demonstrated osmosis. Why?

III. Selective Permeability of Membranes

1. The data shows that diffusion will be greater when the concentration gradient is ________________ on either side of the bag. Complete the table and answer the following questions.
Contents of Bag Contents of Beaker
0 min 60 min 0 min 60 min
Starch
Chloride Ion

2. Which substance diffused through the dialysis membrane?

3. Why was this possible?

4. Why did the starch molecule show negative in the beaker?

IV. Tonicity

1. Draw two illustrations of a single Elodea cell:
a. One in a fresh water solution (hypotonic, cell is turgid)
b. One in a cell in a 40% sucrose solution (hypertonic, cell is plasmolyzed).
c. Include arrows to show the net direction of water flow relative to each cell.
d. Label cell wall, chloroplasts and plasma membrane on both drawings.
e. Sign, date and prepare an image of your drawings and include it with this lab report.

Isotonic Solution Hypertonic Solution Hypotonic Solution
Solute outside cell Same concentration on both side of cell membrane More concentration of solute than of water outside the cell Lesser concentration of solute than of water outside the cell
Net osmosis of water Equal both in and out of cell membrane Net osmosis of water
out of the cell Net osmosis of water
into the cell

2. In Ex 5 and 6 you observed tonicity changes in Elodea cells and in red blood cells. Using the table above compare what happens to a Red blood cell in different solutions. Use these terms in your description. Use the terms equilibrium, hemolysis, and crenation to fill out the table below.

Hypertonic solution
10% salt solution Isotonic solution
.9% salt solution Hypotonic solution
.45% salt solution
Red Blood Cell
Appearance
Term Used

Summary Questions

1. Osmosis is the diffusion of _____________ across a ___________________ membrane from an area of _____________ concentration to an area of ___________ concentration until equilibrium is reached.

Example:

2. Diffusion is the net movement of ______________ down their concentration gradient until _______________ is reached. Give an example.

Examples:

3. In what direction will osmosis occur if a 35% sugar solution is separated from a 15% sugar solution by a selectively permeable membrane?

4. In Ex 4, what was the difference between the starch and chloride ion that affected diffusion through the dialysis tubing?

5. Which of the following variables was not demonstrated to effect diffusion and osmosis in this lab? Highlight your answer.

a. Effect of temperature on speed of diffusion
b. Effect of molecular weight on speed of diffusion
c. Effect of concentration of solutes on osmosis through a dialysis tube membrane
d. Effect of electrical gradient on two sides of a membrane
e. Effect of tonicity on osmosis of water through animal and plant cell membranes

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