ZOOL 141L – Anatomy and Physiology Lab

Diffusion and Osmosis Laboratory Exercise

Introduction

In this laboratory exercise, we will investigate the processes of diffusion and osmosis. Please read the corresponding ZOOL 141 textbook information on diffusion, osmosis and cell membrane transport processes.

This lab consists of three activities:

1. Diffusion of colored dyes through agar (Diffusion of Methylene Blue and Potassium Permanganate Experiment).

2. Osmosis of water in simulated “cells” (Osmosis Experiment).3. Diffusion/osmosis in potato tissues (Potato Experiment)

Your formal report for this lab activity will be described in class.

Diffusion of Methylene Blue and Potassium Permanganate Experiment

In this experiment, we will compare the diffusion rates of two colored dyes, methylene blue (MB) and potassium permanganate (PP), in agar. Agar forms a gel-like material. Diffusion is the process whereby we observe net transport of molecules from an area of high concentration to an area of low concentration. This net transport is a consequence of a spontaneous physical process resulting from physical laws governing the behavior of matter and energy (specifically the second law of thermodynamics). Several factors may influence these diffusion rates: temperature, concentration gradient, and molecule size (molecular weight). Increasing the temperature increases molecular motion and, therefore, the rate of diffusion. Also, a higher concentration gradient we lead to higher net diffusion rates. However, increasing molecular size reduces the rate of diffusion. For the purposes of this experiment, the temperature and concentration gradient will be the same for both dyes. Therefore, only the factor that will be different between the dyes is their molecular weights.

Molecular Weight:

Methylene Blue (MB): ________________________ (fill in)

Potassium Permanganate (PP): ________________ (fill in)

Procedures

1. Form a hypothesis on diffusion rate of MB and PP.2. Each team of 2 should have 2 agar plates.3. Place 1 drop of MB and 1 drop PP of on an agar plate. Place the drops away

from each other, but not too near the edge.

4. Repeat this procedure with the 2nd plate.5. Measure the initial diameter (time = 0 minutes; T0) of the drop and measure in

mm.6. Measure the final diameter 60 minutes later (time = 60 minutes; T60).7. Enter your data into Table 1.8. Place all group data on the board and enter into Table 2.9. Calculate the averages from the class data and enter these values into Table 2.10.Do the data support your hypothesis? Explain.

Table 1. Rate of Diffusion in Methylene Blue vs Potassium Permanganate at Room Temp in mm/hr.

MB T0 (MM)

MB T60(MM)

RATEMM/HR

PP T0 (MM)

PP T60(MM)

RATEMM/HR

PLATE 1

PLATE 2

AVERAGE AVERAGE

PPMB

Table 2 Group Data of Rate of Diffusion in Methylene Blue vs Potassium Permanganate at Room Temp in mm/hr.

GROUPMB RATE

MM/HRPP RATE MM/HR

1

2

3

4

5

6

7

8

9

10

AVERAGE

Osmosis Experiment

In this experiment, you will examine the process of osmosis across a semipermeable membrane. Osmosis is the special case of diffusion of water molecules across a membrane with pores large enough to allow the water molecules through, but not larger molecular solutes (e.g., sucrose) dissolved in the water. When such a membrane divides two aqueous solutions where one has a higher solute concentration than the other, then there will be net transport of water from the low-solute solution into the high-solute solution. Our semipermeable membrane in this study will be dialysis tubing segments that will be tied off to enclose different concentrations of sucrose (our solute) as simulated “cells.” While water molecules can pass easily through the membrane, sucrose molecules cannot. You will be working with four different “cells” each with a different concentration (0%, 10%, 20%, and 40%) of sucrose. These cells (dialysis bags containing different sucrose concentrations) will each be place into beakers containing 10% sucrose. But you will not know which “cell” contains which sucrose concentration. Your task will be to determine the sucrose concentration of each “cell” by measuring the water uptake (or release) of each “cell.” Water uptake will be determined by the change in weight (due to uptake of water) of each of your “cells” after immersion in 10% sucrose.

Procedures

1. Form a hypothesis. Predict the weight changes of different cells according to the concentration of the sucrose solution inside each one of them. See example below.

2. Work in teams of 43. Rinse 4 dialysis tubes in water to open them and tie a knot at one end. These will

represent a “cell”.4. Using pipette, fill one cell with 10 ml of one of the colored sucrose solutions (red,

blue, green or yellow). Tie a knot at the other end, avoiding leaving any air in the cell. Trim off any excess tubing. Repeat this with the three other tubes using the other colored solutions.

5. Gently wipe the tubes dry and weight the tube on a balance.6. Set up 4 beakers of 50 ml 10% sucrose solution.7. Place 1 tube in each beaker.8. Wait 30 minutes, remove tube, gently pat dry and reweigh.9. Enter your group values into Table 3.10.Enter class data into Table 4.11.Calculate the averages from the class data and enter these values into Table 4.12.Determine the sucrose concentrations for each cell and enter your conclusions

into Table 413.Do the data support your hypothesis? Explain.

Hypothesis Example:

H1a. A cell place in a 10% sucrose solution that does not gain or lose any considerable weight in comparison to the other cells contains 10% sucrose and is isotonic.

Form 3 other hypothesis for the other unknown solutions.

H1b.

H1c.

H1d.

Figure 1. Using a pipet to take 10ml of unknown colored sucrose solution.

Figure 2. Make 4 sacs using dialysis tubes. Fill with 10 ml unknown sucrose solution

Figure 3. After weighing sacs, place in 50 ml 10% sucrose for 30 minutes.

50 ml 10% sucrose

TABLE 3. DATA FOR OSMOSIS EXPERIMENT USING UNKNOWN SUCROSE SOLUTIONS (0, 10, 20, 40%):

CELL

INITIAL WEIGHT(IW) grams

FINAL WEIGHT(FW) grams

WEIGHT CHANGE(FW – IW) grams

RED

BLUE

YELLOW

GREEN

TABLE 4 GROUP DATA FOR OSMOSIS EXPERIMENT USING UNKNOWN SUCROSE SOLUTIONS (0, 10, 20, 40%):

GROUP

CELL’S WEIGHT CHANGES (FW – IW) grams

RED BLUE YELLOW GREEN

1

2

3

4

5

6

CLASS AVERAGE WEIGHT CHANGE

% OF SUCROSE INSIDE OF THE CELL

SOLUTION INSIDE OF THE CELL(HYPOTONIC, HYPERTONIC, ISOTONIC)

SOLUTION OUTSIDE OF THE CELL(HYPOTONIC, HYPERTONIC, ISOTONIC)

Questions

1. Define osmosis.

_____________________________________________________________________

2 In what direction will water move across the cell membrane in Fig. A; into the cell, out

of the cell or in both directions?

3. In Fig. B, does the cell gain wt., lose wt., or there is no change in wt.?

4. The cell in Fig. C is ________ (hypotonic, hypertonic or isotonic) and the solution is

________ (hypotonic, hypertonic or isotonic).

Fig. CFig. B

10% sucrose

3% sucrose

10% sucrose

40% sucrose

10% sucrose

10% sucrose

Fig. A

Potato Experiment

In this exercise, we will be studying living plant cells (potato cells). Pieces of potato will be placed in distilled (pure) water or water containing 10% sucrose. You will measure the weight change that takes place in these two pieces of potato. From the understanding of diffusion and osmosis that you have gained, you will need to interpret the results of this experiment.

Procedures

1. Form a hypothesis on whether a potato core will gain or lose weight if placed in freshwater or a sucrose solution.

2. Work in a group of 43. Cut 2 potato cores.4. Gently pat the potato cores dry and weigh (time = 0; T0 weight). Enter these

values in Table 5.5. Set up 2 beakers, one with 50 ml of distilled water and the other with 50 ml 10%

sucrose.6. Place a potato core in each beaker for 30 minutes. Be sure to keep track of

which potato core went into each beaker.7. Remove the potato cores after 30 minutes, pat gently and reweigh (time = 30

minutes; T30 weight). Be sure to keep track of which potato core went into each beaker. Enter these value in Table 5.

8. Enter class data into Table 6.9. Calculate the averages from the class data and enter these values into Table 6.10.Do the data support your hypothesis? Explain

Figure 5. Potato Core

Table 5. Potato weight after 30 minutes immersion in distilled water or 10% sucrose.

TIMEPOTATO WEIGHT IN

DISTILLED WATER (g)POTATO WEIGHT IN 10%

SUCROSE (g)

T0

T30

CHANGE IN WEIGHT

Table 6. Change in potato weight after 30 minutes immersion in distilled water or 10% sucrose.

GROUPCHANGE IN POTATO WEIGHT

IN DISTILLED WATER (g)CHANGE IN POTATO WEIGHT IN

10% SUCROSE (g)

1

2

3

4

5

6

CLASS AVERAGE