BI205: Introductory Biology II
Week 4 Lab
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Week 4 Lab: Osmosis and Diffusion
Introduction
In this experiment, we will investigate the effect of solute concentration on osmosis. A semi-
permeable membrane (in this case, dialysis tubing) and sucrose will create an osmotic
environment similar to that of a cell. The dialysis tubing is similar to a cellular membrane, in
which the membrane is permeable to water but not to sucrose. This selective permeability
allows us to examine the net movement of water across the membrane.
Before you begin, review the diffusion and osmosis materials available in “How Life Works”
section 5.2, and the associated animations in LaunchPad.
There are three parts to this lab:
Part I: Experimental Setup
Part II: Experimental Procedure
Part III: Lessoned Learned
Parts I & II must be done consecutively, with an estimated total time investment of 2-2½ hours.
Materials
You will use the following items from your BI 205 Escience lab kit:
(Quantity 2) 250 mL beakers
600 mL beaker
10 mL graduated cylinder
100 mL graduated cylinder
(5) 15 cm pieces of dialysis tubing
(10) rubber bands - 2 each of blue, green, red, yellow and white
#
60 g sucrose (sugar) powder, C
12
H
22
O
11
Waste beakers (any volume)
Digital scale
#
Some kits may not include the white rubber bands. In such cases, you may substitute standard
rubber bands or skip rubber bands for the 5
th
dialysis bag. If rubber bands are not available,
simply tying knots should be sufficient to seal the ends of the bag, and you will be able to easily
tell it apart from the 4 other bags.
You are expected to provide the following items for use in this experiment:
Water
Permanent marker
Scissors
Paper Towel
Digital camera (a phone camera is just fine).
BI205: Introductory Biology II
Week 4 Lab
Page 2 of 9
(2) different liquids that contain sugar at an unknown concentration (for example: juice,
soda, water with dissolved honey, etc.). It might be interesting, for example, to test a
regular drink vs. a diet version.
Part I: Experimental Setup
1.
If your balance does not say “auto calibration” on the outside of the box (see note in
Canvas--most of you will have the auto calibration balance), you will need to calibrate your
digital balance. Open the lid of the scale and follow the calibration procedure. Instead of
using a 500 g weight to calibrate the scale, you will fill your 600 ml beaker with 468 ml of tap
water. Because water is 1 g per ml and the beaker weighs 32 g, this will be an accurate 500
g weight for calibration.
Use your 10 mL and 100 mL graduated cylinders to measure the
468 mL of tap water.
2.
Use your permanent marker to label two 250 mL beakers as “1” and “2”.
3.
Cut five strips of dialysis tubing, each 15.0 cm long.
4.
Fill Beaker 2 with 100 mL of water and submerge the cut pieces of dialysis tubing in the
water for at least 10 minutes. This will hydrate the tubing membranes and prepare them for
use in your experiments.
