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Topic 3: Movement of Substances
Cells need to eat in order to grow, divide and carry out life
functions.
They also need to get rid of wastes substances.
But they don’t have a mouth or anus to do so. Substances get
in and out of cells, but HOW???
Diffusion.
Molecules of a gas, a liquid or a dissolved substance will move
from a region where there are a lot of them (i.e. concentrated)
to regions where there are few of them (i.e. less concentrated)
until the concentration everywhere is the same.
Whether this will happen or not depends on whether the cell
membrane will let the molecules through.
Rates of diffusion.
The speed with which a substance diffuses through a cell
membrane will depend on:
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
 temperature
 pressure
 distance to diffuse
 concentration in and out of the cell
 size of the molecules or ions to diffuse.
Sometimes in the cell membranes there are pores which will
allow diffusion of certain substances only and this is called
controlled diffusion.
If the surface area of the cell is bigger, the more the
substances go in or out faster and therefore, the rate of
diffusion is said to be higher.
Active Transport.
Sometimes, when on both sides of a cell the concentrations
are equal, some substances would still need to pass to a side
of them. This wouldn’t occur simply by diffusion and a kind of
energy needs to push the substances in the particular
direction. This occurs by active transport.
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Osmosis.
Osmosis is the special name used to describe the diffusion of
water across a membrane, from a dilute solution to a more
concentrated solution.
The cell membrane.
The cell membrane is said to be partially permeable. This is
because it allows some substances to get in and out. It has
small pores or carriers which allow the movement of these
substances.
Water Potential.
Pure water is said to have the highest water potential because
it is a solution which contains the highest amount of water
molecules in it. A salt solution contains of salt molecules and
water molecules, so it has a lower water potential than the
pure water because it contains less water molecules.
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Osmosis in animal cell.
There is a higher concentration The extra water makes the cell
of free water molecules outside swell up.
the cell than inside, so water
diffuses into the cell.
Plant Cells.
Because there is effectively a lower concentration of water in
the cell sap water diffuses into the vacuole and makes it push
out against the cell wall causing turgor not flaccid.
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Biology classwork.
1. Diffusion occurs when a gas, a liquid or a dissolved substance
will move from a region of __________ concentration to a region of
________ concentration. (low, high, medium).
2. Rates of diffusion depend on: ______________, ________________,
_________________, _______________.
3. Active transport is when substances are pushed in or out of a
cell using en_____.
4. Osmosis is the special name used to describe the diffusion of
_____________ across a membrane, from a dilute solution to a
more concentrated solution.
5. A pure water solution has the highest __________ potential.
6. A 10% solution of copper sulphate is separated by a partially
permeable membrane from a 5%
solution of copper sulphate.
Will water diffuse from the 10% to the 5% solution or from the
5% to the 10% solution?
If a fresh beetroot is cut up, the pieces washed in water and then
left for an hour in a beaker of water, little or no red pigment
escapes from the cells into the water. Bearing in mind the
properties of a living cell membrane, offer an explanation for this
difference.The Effects Of Osmosis on Living Cells.
When too much water enters living cells, these fill up and expand.
protected with a cell wall so they cannot burst. They are said to be
animal cells do not have a cell wall and they can burst.
Plant cells are
turgid. However,
They are undergoing
haemolysis. When cells lose water, they tend to shrink. Animal cells are undergoing
crenation while plant cells are plasmolysed. Plasmolysis occurs when the plant cells
lose too much water and the membrane becomes detached from the cell wall.
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Contractile Vacuoles
Unicellular organisms need specialised mechanisms so that if they find themselves in
dilute aquatic environment they don’t burst.
Amoeba is a unicellular animal like
organisms. This has contractile vacuole that is a space within the cytoplasm of the
organism which can fill with water and the excess water can be expelled from the cell
later.
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Practical Work: Observing diffusion of a gas.
Aim: What is the aim of this experiment?
Apparatus: ______________ , _________________, ______________
_________________, ______________________, ____________________
Method:
1. Having the above apparatus, how would you design this
experiment as to observe diffusion in a gas?
2. Why do we use red lithmus paper and ammonia?
3. Do you think ammonia is volatile?
4. How would you set up the apparatus as to see ammonia gas
moving from one place to another?
5. From which direction to what other direction does ammonia
move: from high concentration to low concentration or from
low to high?
Results:
1. How did you see ammonia travelling?
2. What was the colour change of red lithmus paper?
Conclusions:
1. Why was it important to wet the lithmus paper before
starting the experiment?
2. What is diffusion?
3. Did diffusion occur in this experiment?
Movement of Substances in and out of cells.
Focusing and planning.
1. What is osmosis?
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
2. What happens to a plant cell if it is placed in a
concentrated solution?
3. What happens to a plant cell if it is placed in a dilute
solution?
4. Given the following apparatus how would you plan an
experiment to observe the effect of osmosis on plant
cells?
Beakers, stirrer, water, potato, sugar
5. What do you think will happen and why?
6. What is a solution that is more concentrated than
another solution called?
7. What is a solution that is less concentrated than another
solution called?
8. What is a solution that has equal concentration as
another solution called?
Gathering Information.
Group
Size of chip
In water
In sugar
A
B
C
D
E
Processing and Interpreting.
1. Why are we comparing the results of 5 groups?
2. Were the results consistent?
3. What happened to the potato chips that were placed in
hypertonic and hypotonic solutions?
4. Why did the potatoes that were put in a hypertonic
solution shrink?
5. Why did the potatoes that were put in a hypotonic
solution grow?
Ms J. Ebejer Grech B.Ed. (Hons.)
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Topic 3: Movement of Substances
Osmosis in potato cells.
Aim: To study osmosis in potato cells.
Apparatus: potato, knife, sugar, water and petri-dishes.
Method:
1. The potato was pealed and cut into 2.
2. Their interior was scooped out so that a cup-like
structure was made.
3. The potatoes were labelled A and B.
4. Using distilled water and sugar, how would you continue
this experiment as to show osmosis?
Results:
What did you observe?
Conclusions:
1. Explain in terms of osmosis what happened.
Osmosis in Visking Tubing.
Aim:
To demonstrate that the visking tubing is semipermeable and that osmosis occurs through it.
Apparatus: boiling tube, visking tubing, elastic band, iodine,
starch, water.
Method: How would you use the above apparatus as to show
osmosis?
Results: What happened to the white mixture inside the
visking tubing?
What happened to the yellow mixture outside the visking
tubing?
Ms J. Ebejer Grech B.Ed. (Hons.)
Topic 3: Movement of Substances
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Conclusions: Explain in terms of osmosis why the iodine
entered the visking tubing towards the starch, and why the
starch didn’t exit the visking tubing.
Ms J. Ebejer Grech B.Ed. (Hons.)