Biology

1. 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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2. • 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?
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3. • 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:
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4. • 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:
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5. • 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:
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6. • 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:
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7. • Diffusion happens when a substance is more
concentrated in one place than another.
• This difference in concentration is called a
concentration gradient.
• Molecules are moving randomly due to their
kinetic energy, but the net movement will be
from a high concentration to a low concentration.
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8. • Sometimes a cell needs to take in a substance
against a concentration gradient.
• This requires energy released from
respiration.
• The process is called ACTIVE TRANSPORT.
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9. • 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.
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10. • Water moves from a dilute solution to a more
concentrated one across the partially
permeable cell membrane.
Rlawson at en.wikibooks
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11. – 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).
Sugar Molecule
Water Molecule
Partially permeable membrane
High water
concentration
Low water
concentration
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12. – 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).
Sugar Molecule
Water Molecule
Partially permeable membrane
High water
concentration
Low water
concentration
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13. Visking tubing
0.5%
Sugar
solution
0.1%
Sugar
solution
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14. Visking tubing
0.5%
Sugar
solution
0.1%
Sugar
solution
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15. Copyright © 2014 Henry Exham

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17. 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.
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19. At a higher temperature the particles have more kinetic energy and are
moving around faster. Therefore in a given time more diffusion will occur.
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21. 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.
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22. • Three cubes of agar are prepared which
contain the indicator phenolphthalein.
• These are placed in hydrochloric acid which
will diffuse into the cubes.
• As it diffuses in it will turn the indicator
colourless.
3cm
3cm
2cm
2cm
1cm
1cm
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23. • As the size of the cube increases the surface
area to volume ratio decreases.
3cm
3cm
2cm
2cm
1cm
1cm
Width of cube
(cm)
Surface area
(cm2)
Volume
(cm3)
Surface area: volume
1 6 1 6
2 24 8 3
3 54 27 2
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24. • The cubes look like this after a few minutes.
• 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.
3cm
3cm
2cm
2cm
1cm
1cm
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25. • Watch this video to see the experiment in
action.
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26. • 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.
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