Transcript Unit 1: Topic 2 Practical`s

Osmosis and Diffusion
Practical 1
 Learning

objectives:
By the end of the lesson you should be able to:


Explain the movement of water in plant and animal
cells by the process of osmosis.
Describe the effect of osmosis on plant and animal
cells.
 Osmosis is the diffusion of water
Across a selectively permeable membrane
___________________
Visking tubing is an artificial membrane which acts
____________
like a cell membrane
Model cell
 A ___________
can be made by making a bag
out of the visking tubing and filling it with
the appropriate solutions
 To
demonstrate Osmosis
 Method
1.
2.
3.
Your teacher will show
you how to set up the
model cell shown in the
diagram
Dry and weigh the
model cell, then place
it in a beaker and cover
with distilled water.
After 24 hours dry and
reweigh the model cell
10% sucrose
solution
Visking
Tubing
Results
Time
Start
After 24 Hours
Mass (g)
 What
happens to the model cell and
what causes this change?
 The
mass increases due to the
movement of water by osmosis
 What
precautions are taken in this
experiment?
 Making
sure that the model cell is dried
properly so that no water is on the
outside of the bag to affect the mass
readings
Practical 2
 Learning

objectives:
By the end of the lesson you should be able to:



Describe the effect of placing cells in a HYPERTONIC
solution.
Describe the effect of placing cells in an ISOTONIC
solution.
Describe the effect of placing cells in a HYPOTONIC
solution.
Diffusion of water across a selectively
is the________________________________
permeable membrane
_________________
 When plant cells are placed in hypertonic solutions
Osmosis
plasmolysis
then ________
will take place and ________
____ can
be seen
 Osmosis
 To
observe osmosis in cells
1.
2.
3.
Label 2 slides A and B
Make 2 wet slides of the specimen adding
distilled water to A and 10% sucrose
solution to B
After a few minutes observe and draw the
appearance of one cell from slide A and one
from slide B
Slide A Distilled Water
Slide B – 10% sucrose Solution
 What
happens to the cell in 10% sucrose
solution?
The membrane pulls away from the wall
 Why
does this happen?
Water moves out of the vacuole by osmosis
causing the contents to shrink
 What is the name given to this condition?
Plasmolysis
 Why
 To
are the cells left for a few minutes?
allow sufficient time for the process
to occur
Practical 3
 Learning

objectives:
By the end of the lesson you should be able to:



Describe the effect of placing cells in a HYPERTONIC
solution.
Describe the effect of placing cells in an ISOTONIC
solution.
Describe the effect of placing cells in a HYPOTONIC
solution.
 When
placed in solutions which have a different
concentration to its cells, plant tissue will show
change in mass due to osmosis taking place
a _____________________________________
Isotonic
an ___________
solution plant tissue will
neither gain or loose mass.
Hypotonic
 In a _____________
solution plant tissue will gain
mass.
Hypertonic
 In a ______________
solution plant tissue will lose
mass
 In
 To
measure the concentration of cell
sap in potato tissue
1.
2.
3.
4.
5.
Add 20cm of each sucrose solution to 5
labelled boiling tubes using a syringe
Cut 5 thin cores of potato tissue with a cork
borer on a cutting tile and cut them to 2cm in
length with a knife.
Dry the pieces of tissue then weigh them and
record the initial masses in your results table.
Add one core to each tube and leave for 25
minutes at room temperature
Remove the tissue from the solutions, dry,
reweigh and record the final masses in your
results table.
Concentration of
solution (M)
0.1
0.2
0.3
0.4
0.5
Initial Mass (g)
Final Mass (g)




Calculate the change in mass by subtracting the initial mass
from the final mass.
Some of the changes are positive, The core has gained mass.
Some of the changes are negative, the core has lost mass
Calculate the percentage change in mass by dividing the
change in mass by the initial mass and multiplying the
answer by 100.
Concentration of
solution (M)
0.1
0.2
0.3
0.4
0.5
Change in mass (g)
Percentage change in
mass (g)
 Draw
a line graph of these results
+
% Change
in mass
0
0.1
0.2
0.3
0.4
0.5
Concentration of
solution (M)
 The
potato tissue and its surrounding solution
are the same strength when there is no
change in mass. This is identified on the
plotted line at 0% change in mass

What is the concentration of the cell sap in the
potato tissue?
Evaluation
 How could pooling the class results or repeating
the experiment improve the reliability of the
results?
 It would reduce the effect of an unusual result