LAB: Assessing The Effect of Tonicity
and Concentration Gradient On The
Rate of Diffusion and Osmosis In
Dialysis Tubing
PURPOSE
• To assess the effect of different tonicities on the
rate of passive transport in hypothetical cells.
• To observe the effects of different osmotic
potentials on the integrity of these same
hypothetical cells (i.e. cytolysis, turgor,
plasmolysis)
• Method: Immersion of dialysis tubing cells into
baths of varying tonicity
PROTOCOL: Preparing The Systems
• 1) Make sure that your lab station is covered with
paper and that you are wearing an apron
• 2) Fill three beakers with 150mL each of tap
water. Label as systems #1-3 (hypotonic baths).
• 3) The fourth beaker has already been filled with
150mL of 80% glucose. This is system #5
(hypertonic bath)
• 4) System #4 data will be provided by your
instructor.
PROTOCOL: Preparing the Cells
• 4) Open five dialysis tubes using water and a glass
rod. Tie off the bottom of each tube.
• 5) Place 15mL of the following into the respective
tubes and tie off the top leaving only a small air
space. Cut off excess string and tubing.
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System 1: 15mL tap water
System 2: 15mL 20% Glucose
System 3: 15mL 40% Glucose
*System 4: 15mL 80% Glucose (instructor only)
System 5: 15mL tap water
PROTOCOL: Weighing & Immersion
• 6) Make sure that the scale is covered with a glass
plate. Tare the plate, then weigh each of the “cells” (15) to ±0.1g. Record this initial mass in your lab
notebook.
• 7) WHEN YOUR INSTRUCTOR TELLS TO TO DO SO,
immerse each of the cells into its respective
system/bath.
• 8) During the first 10 minute interval, meet at the front
of the room to discuss yesterday’s simulation.
• 9) After 10 minutes, remove each of the cells from the
bath, wipe down the sides of the cell with a paper
towel and reweigh to ±0.1g. Return immediately to the
bath
• 10) Repeat steps 8-9 at 10 minute intervals until 40
minutes have passed.
• 11) Clean up but DO NOT THROW OUT THE
ANALYSIS: Calculation of ∆m
• To assess the effects of tonicity and osmotic
potential on the cells, you will calculate the
change in mass (∆m) for each 10 minute
interval.
• To calculate change in mass for any given
interval, find the difference between the mass
of the cell at that time and the INITIAL MASS.
Note that ∆m may be positive or negative
• Graph ∆m v. time for each of the five systems.
What Is The Connection?
A conceptual problem…
• Q = How do cells feed
and excrete?
• A = Via their cell
membranes
• So therefore, shouldn’t
cells require MORE
surface area?
Lab: Assessing the Rate of Cellular Transport v.
Differing Surface Area to Volume Ratios
• Purpose: To determine how the size of a cell is
related to its ability to perform passive cellular
transport
• Method: ?
Materials: The following materials are available for your protocol
Simulated Cell
Materials
Solutions
Quantifying Tools
Various Lab
Equipment
Safety Equipment
Plain agar
Distilled Water
Electronic Balances
(±0.1g)
Ring Stands w/Clamps
Goggles
6% Salt Agar
6% Salt Water
Rulers
Beakers (600, 250 and
100mL)
Aprons
Agar w/1 %
Phenolthalien
0.1M NaOH
Conductivity Probes
(measuring 0 – 20000
µS)
Glass Stirring Rods
Agar w/1% 0.1M
NaOH
0.1M HCl
pH Probes (±0.1 units)
Scalpels
Vernier LabQuests
What You Need To Collect
• Data: The following components will need to be part of the
data presentation for your inquiry
• A table showing the calculation of surface area to volume
ratios for at least three different sizes of simulated cells (i.e.
agar blocks)
• A table showing the quantification of cellular transport (e.g.
rate of change of conductivity, changes in mass, distance
solutions penetrated into cell, etc.) for each of the different
sizes of simulated cells.
• A line graph (X-Y scatter plot) showing the quantification of
passive transport (part B) v. surface area-volume ratio (part
A)
• Any relevant qualitative observations
Conclusion
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Conclusion: After analyzing the results, write out a formal conclusion that
addresses the following aspects of this investigation.
Restate, then confirm or refute your hypotheses regarding the relationship of
surface-area-volume ratios v. rate of passive transport.
Describe the nature of the relationship between surface area-volume ratios and
rate of passive transport. Is the relationship direct, inverse, optimal or
inconsistent? If a relationship does exist, is it linear or exponential?
Select specific pieces (at least 3) of quantitative data from part B above to support
your contentions regarding the nature of the relationship.
Based upon your information, how would cellular growth during the cell cycle
affect the cell’s surface area to volume ratio? How, in turn, might that impact the
ability of the cell to perform passive transport?
Why would a decline in the rate of passive transport be problematic for the cell in
terms of homeostasis and energy flow?
As such, how might surface area-volume ratios serve as a trigger for cellular
division?
Evaluate your protocol. What confounding variables or sources of error were
present in this inquiry? How might that have specifically impacted your
conclusions (part 2 above)?