Download diffusion_and_osmosis - Help for MYP 4 and 5 Students

MAKING SENSE OF
MOVEMENT IN AND OUT OF CELLS
IGCSE Biology
1.1 Life Processes
Movement in and out of cells
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• Can you write a definition for diffusion, osmosis and
active transport?
• Can you explain how surface area to volume ratio,
temperature, and concentration gradient affect the
rate at which these processes work?
• Can you describe a simple experiment to
demonstrate diffusion using a non-living system?
• In order for the cell to carry out the many
chemical reactions it needs to, substances
must enter and leave the cell.
• This happens in the following 3 ways:
• In order for the cell to carry out the many
chemical reactions it needs to, substances
must enter and leave the cell.
• This happens in the following 3 ways:
• In order for the cell to carry out the many
chemical reactions it needs to, substances
must enter and leave the cell.
• This happens in the following 3 ways:
• In order for the cell to carry out the many
chemical reactions it needs to, substances
must enter and leave the cell.
• This happens in the following 3 ways:
IS THE NET MOVEMENT OF MOLECULES FROM
A REGION OF HIGH CONCENTRATION TO A
REGION OF LOW CONCENTRATION.
THE MOVEMENT IS DOWN THE CONCETRATION
GRADIENT AND REQUIRES NO ADDITIONAL ENERGY
• Diffusion happens when a substance is more
concentrated in one place than another.
• This difference in concentration is called a
.
• Molecules are moving randomly due to their
kinetic energy, but the net movement will be
from a high concentration to a low concentration.
Particles moving from high
to a low concentration.
• Sometimes a cell needs to take in a substance
against a concentration gradient.
• This requires energy released from
respiration.
• The process is called
.
Particles moving from low to
a high concentration.
IS THE MOVEMENT OF MOLECULES FROM A
REGION OF LOW CONCENTRATION TO A
REGION OF HIGH CONCENTRATION.
THE MOVEMENT IS UP THE CONCETRATION GRADIENT AND
REQUIRES ENERGY FROM THE CELL
• Active transport occurs in the roots of plants
to move minerals into them against the
concentration gradient and also in the small
intestine of animals.
• Water moves from a area of high water
potential (higher concentration of water) to
an area of low water potential (lower
concentration of water) across a partially
permeable cell membrane.
Low water
concentration
Sugar Molecule
Water Molecule
High water
concentration
Partially permeable membrane
Rlawson at en.wikibooks
Low water
concentration
High water
concentration
Sugar Molecule
Water Molecule
Partially permeable membrane
– In osmosis, water moves from an area of high water concentration
(pure water or a dilute solution) to an area of low water concentration
(a more concentrated solution of sugar or another solute).
– Water passes through a partially permeable cell membrane.
– This type of membrane has tiny holes (pores) through which very small
molecules (including water) can pass, but not larger molecules (such
as sugar and proteins).
Low water
concentration
High water
concentration
Sugar Molecule
Water Molecule
Partially permeable membrane
– In osmosis, water moves from an area of high water concentration
(pure water or a dilute solution) to an area of low water concentration
(a more concentrated solution of sugar or another solute).
– Water passes through a partially permeable cell membrane.
– This type of membrane has tiny holes (pores) through which very small
molecules (including water) can pass, but not larger molecules (such
as sugar and proteins).
Osmosis in plant cells
• Osmosis plays an important role in plants, especially
non- woody ones.
a) A plant cell is immersed in distilled water, the
following diagrams show what happens.
The following changes take place:
1. Water moves into the cell through the cell membrane
2. Cytoplasm & cell vacuole increase in volume.
3.Increase in cell volume increases internal cell pressure, which
forces the cytoplasm to push against the cell membrane.
4.Cell membrane pushes against the cell wall.
Cell becomes TURGID
The cell becomes firm, we say it is
turgid. As a result, The plant’s stem is
upright and stiff.
Why is turgidity important for:
• a plant, in general?
1. Holds plant stems upright
2. Important in the functioning of the stomata
b)Plant cell is placed in a concentrated solution.
Gaps between
cell wall & cell
membrane fill
with solution
•Water moves out of cell via osmosis
•Cell membrane shrinks away from cell wall
The following changes take place:
• 1 Excess water moves out of the cell
• 2 Excess loss of water shrinks cell vacuole &
cytoplasm, which radically reduces internal cell
volume
• 3 cell membrane pulls & cytoplasm away from cell
wall
The cell become plasmolysed because
excess water has been lost through the
cell membrane.
C) Plant cell is placed in a low concentrated solution.
The following changes take place:
1. Water moves out through cell membrane
2. Loss of water from inside the cell reduces the internal volume
of the cell.
3. Cytoplasm no longer pushes against cell wall.
4. Reduced internal volume of cell leads to a reduced internal
pressure. Cell becomes FLACCID.
The cell has become flaccid. Leaves
droop and collapse.
Osmosis in animal cells
• a) in distilled water, an animal cell bursts:
Why is this different from plant cells?
• b) In a concentrated sugar or salt solution,
the animal cell shrinks and shrivels.
Osmosis in red blood cells.
a) Red blood
cells in distilled
water.
b) Red blood cells
in equilibrium.
c) Red blood cells
in a concentrated
solution.
0.5%
Sugar
solution
0.1%
Sugar
solution
Visking tubing
0.5%
Sugar
solution
0.1%
Sugar
solution
Visking tubing
Water moves from a dilute solution to a more concentrated one across the
partially permeable cell membrane.
The surface area of the second cell is much bigger than the first cell due to
the folded membrane. The volume of the cells is very similar. Therefore the
second cell has a much larger surface area to volume ratio and it increases
the rate of diffusion.
At a higher temperature the particles have more kinetic energy and are
moving around faster. Therefore in a given time more diffusion will occur.
When there is a big difference between the number of particles in one place
and another diffusion will happen much faster then if they are already quite
spread out.
3cm
2cm
1cm
• Three cubes of agar are prepared which
contain the indicator phenolphthalein.
1cm
2cm
3cm
• These are placed in hydrochloric acid which
will diffuse into the cubes.
• As it diffuses in it will turn the indicator
colourless.
3cm
2cm
1cm
• As the size of the cube increases the surface
area to volume ratio decreases.
1cm
3cm
2cm
Width of cube
(cm)
Surface area
(cm2)
Volume
(cm3)
Surface area: volume
1
6
1
6
2
24
8
3
3
54
27
2
3cm
2cm
1cm
• The cubes look like this after a few minutes.
1cm
2cm
3cm
• If these were real cells then the bigger cell
would not have received what it needs to all
parts of the cell.
• Therefore it would need a bigger surface area
in order to rely on diffusion.
• Watch this video to see the experiment in
action.
Surface Area
• As the rate of diffusion relies on the surface
area.
• The parts of organisms that rely on diffusion
therefore tend to have a large surface area.