Unit 1 VCE Biology Outcome Task
Name:
Outcome Task 2
Exploring diffusion and osmosis
Introduction
The survival of a cell depends on being able to control what goes in and what goes out. The cell
requires specific amounts of oxygen, water and glucose to allow it to respire. The cell also
needs to remove Carbon Dioxide as it’s a by product. How does this occur? What are properties
of the plasma membrane that determines what substances can enter or leave a living cell.
Hypothesis
Purpose
To investigate the movement of different substances through a differentially permeable
membrane by modelling a plasma membrane.
Procedure and Materials
(a) Place a small amount of starch solution
onto a clean slide. Add a drop of iodine.
Record any colour changes in table 1
under observations.
(b) Place a small amount of glucose solution
onto a clean slide. Dip some Test-tape
into the solution and record any colour
changes in table 1
(c) What conclusions can you draw from
these two simple tests? Record your
answers in table 1
(d) Fill a beaker with water and let the
dialysis tubing sit in it for a few minutes
while you collect the rest of equipment.
There are two sets of equipment to
prepare; depending on the size of the
group and equipment available you may
decide to prepare both simultaneously.
(e) Set up the retort stand with boss head and clamp.
(f) Three-quarters fill the gas jar with water add iodine solution until there is a noticeable
colouring in the gas jar.
(g) Take the dialysis tubing and holding it under a gently running tap. Carefully, rub the top of
the tubing between your thumb and forefinger until the tube opens and water can run freely
Unit 1 VCE Biology Outcome Task
Name:
out of the bottom.
.
.'
(h) Tie a knot in one end. It is easier to make the knot higher than you need it, and then slide it
down before tightening it. Make sure the knot is not too close to the bottom of the bag, as it
may leak. Again, be careful not to tear the tubing, but make sure the knot is tight. Fill with
water from the tap to make sure it ho1ds water without leaking. Empty the water out.
(i) Wrap several loops of a rubber band around the bottom of the thistle funnel stem and move
it up a
(j) Few centimetres. Put the thistle funnel stem inside the top of the dialysis tubing and wrap
the tubing tightly around the stem. Stretch the rubber band loops down around the dialysis
tubing so it is held firmly in place. (Alternatively, you could try pushing the rubber band
over the whole dialysis tubing and stem initial1y; but putting it on the stem first eventually
makes it easier.)
Results
Test 1 Baselines
Test
Test 2 Starch bag activity
Solution in gas jar
Observations
Solution in bag
Conclusions
Solution level in the
thistle tube
Unit 1 VCE Biology Outcome Task
Test 3 Glucose bag activity
Test-tape of water in gas jar
Name:
Change in the height of the solution in the
thistle funnel tubing
Discussion
Starch bag activity
1. Give a reason to explain the colour change that you observed in the bag containing the
starch solution. What evidence do you have to support your suggestion?
2.
a) Explain how this colour change occurred when the iodine was placed in the gas jar not
in the solution in the dialysis bag.
b) Give a reason to support this idea.
c) From your observations, what can you conc1ude about the relative molecular sizes of
iodine and starch molecules?
3. Explain the role that the dialysis bag played in this experiment. If this was a model of a cell,
what part of the cell wou1d the dia1ysis tubing represent?
4. Did the level of the solution in the thistle funnel change? If it did, explain why?
Unit 1 VCE Biology Outcome Task
Name:
Glucose bag activity
5. Did the colour of the Test-tape change at any time during the experiment? Explain why.
6. Did the water level in the thistle funnel change throughout the experiment? Explain why and
include the term osmosis in your answer.
7. If these experiments model the movement in and out of a cell, what is a factor in
determining whether a substance can enter or exit a cell?
8. Explain what you understand by the term differentially permeable membrane.
Conclusion
How did these set-ups model the structure and function of a plasma membrane? What is it about the
molecule and the plasma membrane that determines whether it can pass through or not!