B4-06 investigating osmosis

1. IB4.6.2H Images
Investigating osmosis
Learning Outcomes:
describe the process of osmosis (grade C)
plan and perform an investigation into
osmosis in plant tissue (Grade C)
Keywords-
Osmosis, partially permeable
membrane, concentration, particles
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2. IB4.6.2H Images
why water is so important to
cells/living things?
What happens if people do not
have enough water?
*You should be able to answer these
questions using scientific ideas and keywords
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3. IB4.6.2H Images
Potato slices or cylinders are used as
models for plant cells in this investigation
Suggest how you could find out whether
the potato gained or lost water
*The mass at the start and end can be used as the dependant variable
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4. IB4.6.2H Images
Set up osmosis activity 1 from
Activity AB4.6.1 Diffusion and
osmosis, to give time for osmosis to
have an effect.
*We carried out this investigation
using the potato slices and sucrose
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5. IB4.6.2H Images
Diagrams a and b show how water molecules move
during osmosis. In this example the membrane
allows water through but the glucose molecules
are too big to get through
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6. IB4.6.2H Images
Findings from the experiment and interpret the changes
in terms of water moving in and out of cells by osmosis.
plant cells have rigid cell walls, so are fairly robust.
However, animal cells burst or shrink due to osmosis.
class results do they show a trend?
potato cylinders in pure water increase in mass;
in very sugary solutions their mass will decrease.
Outlying measurements that are outside the
trend line may be incorrect.
Identify outliers. What should happen to the outliers?
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7. IB4.6.2H Images
The photographs show the same plant. In the right hand image, the plant is
shown after it has not been watered for 10 days. Notice how the structure
has changed as the plant cells have dried.
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8. IB4.6.2H Images
Observe osmosis in action using Video IB4.6.4
Paramecium and complete Osmosis activities 2
and 3 from Activity AB4.6.1 Diffusion and
osmosis.
Complete second measurement of potato
cylinders for osmosis activity 1 and complete
table of results
*Recall the outcome of the investigation: in water alone (as a control),
the potatoes gained mass, in sucrose solution they lost mass, you
should be able to explain this using keywords and scientific ideas
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9. IB4.6.2H Images
1.The normal blood cells are rounded and bi-concave,
whereas the abnormal cells are irregular/spiked.
2. The diameter is about 6–7 µm.
3. As the salt concentration of the solution increases, the
diameter of the red blood cells decreases.
4. The red blood cells are losing water by osmosis, causing the
cells to shrink.
5. 0.45–0.65 g/cm3 (depending on the estimate of diameter
from question 2). This is the concentration where the cells
have a ‘normal’ diameter, so are not gaining or losing water by
osmosis.
6. They have swollen and burst.
*Answers to questions set about blood cells and osmosis (worksheet)
© Oxford University Press 2011