1. Movement in and out of cells
IGCSE Biology
Movement in and out of cells
Understand the process of diffusion, osmosis and active transport
23 May 2019

2. Learning objectives Define diffusion
Plan an investigation to observe diffusion
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3. The Cell
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. The Cell
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:
Diffusion
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5. The Cell
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:
Diffusion
Active Transport
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6. The Cell
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:
Diffusion
Active Transport
Osmosis
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7. Particles moving from high to a low concentration.
Diffusion
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.
Particles moving from high to a low concentration.
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8. Visking tube experiment
Which way will the water move?
Water
Sugar solution
Which way will the Sugar move?
Visking tubing
3 different sugar solutions- which will diffuse the fastest?
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9. Test with Benedicts solution
1g of sugar dissolved in 100ml of water
Wait for 10 mins
2g of sugar dissolved in 100ml of water
Test with Benedicts solution
3g of sugar dissolved in 100ml of water
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10. Learning objectives Describe the factors that influence diffusion
Plan an investigation to observe how various factors effect diffusion
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11. Factors affecting the rate of diffusion
Surface area to volume ratio
Temperature
Concentration gradient
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12. Surface area to volume ratio
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13. Surface area to volume ratio
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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14. Experiment to investigate surface area to volume ratio
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
2cm
1cm
1cm
2cm
3cm
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15. Experiment to investigate surface area to volume ratio
As the size of the cube increases the surface area to volume ratio decreases.
3cm
2cm
1cm
1cm
2cm
3cm
Width of cube (cm)
Surface area (cm2)
Volume (cm3)
Surface area: volume 1 6 2 24 8 3 54 27
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16. Experiment to investigate surface area to volume ratio
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
2cm
1cm
1cm
2cm
3cm
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17. Experiment to investigate surface area to volume ratio
Watch this video to see the experiment in action.
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18. 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.
Alveoli in the lungs
Root hairs
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19. Temperature Low temp High temp
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20. Temperature Low temp High temp
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. Temperature Low temp High temp
Plan an investigation to see if diffusion does occur faster at higher temperatures
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22. Concentration gradient
Low concentration gradient
High concentration gradient
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23. Concentration gradient
Low concentration gradient
High concentration gradient
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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24. Concentration gradient
Low concentration gradient
High concentration gradient
Plan an investigation to see if this is true
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25. Learning objectives Define osmosis
Plan an investigation to observe osmosis
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26. Osmosis
Water moves from a dilute solution to a more concentrated one across the partially permeable cell membrane.
23 May 2019
Rlawson at en.wikibooks

27. Low water concentration High water concentration
The process of osmosis
Low water concentration
High water concentration
In osmosis, water moves from an area of high water potential (pure water or a dilute solution) to an area of low water potential (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
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28. Osmosis Demonstration
Which way will the water move?
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.
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29. Investigating Osmosis
Basic investigations into osmosis can be done on non living systems such as the one showed earlier using visking tubing.
However we can also do investigations using living cells, such as blood cells in animals or cells from a potato for plants.
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30. Investigating Osmosis
Method to investigate the water concentration inside the cells of a potato.
Use a cork borer to take 5 cores from one potato.
Cut of any skin.
Then use a ruler and scalpel to trim them all to 4cm.
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31. Investigating Osmosis
Method to investigate the water concentration inside the cells of a potato.
Blot the cylinders using paper towels to remove excess water.
Use a balance to record the mass of each cylinder.
Add each one to the following salt solutions and leave for 15 minutes.
Cylinder
Salt Solution (M)
Initial Mass (g) A
0.0 B
0.2 C
0.4 D
0.6 E
1.0
A B C D E
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32. Investigating Osmosis
Method to investigate the water concentration inside the cells of a potato.
Remove the cylinders using forceps.
Blot the excess water off them and record the final mass in the table.
Calculate the change in mass for each cylinder and add it to the table.
Cylinder
Salt Solution (M)
Initial Mass (g)
Final Mass (g)
Change in Mass (g) A
0.0 B
0.2 C
0.4 D
0.6 E
1.0
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33. Investigating Osmosis
Method to investigate the water concentration inside the cells of a potato.
To make the results valid calculate the % change in mass for each cylinder using the following equation.
% change in mass = change mass x 100
original mass
Cylinder
Salt Solution (M)
% Change in mass A
0.0 B
0.2 C
0.4 D
0.6 E
1.0
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34. Investigating Osmosis
Method to investigate the water concentration inside the cells of a potato.
The solution closest to 0 is the most similar to the concentration of solutes inside the potato cells. You could plot a graph of salt concentration against % change in mass to get a closer prediction.
% Change in Mass
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Salt Concentration (M)

35. Learning objectives Explain the process of plasmolysis
Plan an investigation to observe the effect that hypotonic, hypertonic and isotonic solutions have on plant cells
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36. Uptake of water by plants
Water is absorbed into the roots by osmosis.
This is because there is a high concentration of minerals in the root cells and therefore a low water concentration compared to the soil.
The cells on the outer layer of the roots are specialised cells called root hair cells
Root hair cell
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Root Tip

37. Root Hair Cell
These root hair cells greatly increase the surface area for osmosis.
H2O
H2O
H2O
H2O
H2O
H2O
Root hair cell
H2O
H2O
H2O
H2O
H2O
H2O
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38. Water enters the cell by
Osmosis in plant cells
What happens if a plant cell is placed in pure water?
Water enters the cell by
osmosis and
becomes turgid.
Water moves from a dilute solution outside the cell to a more concentrated one inside across a partially permeable cell membrane.
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39. Water leaves the cell by
Osmosis in plant cells
What happens if a plant cell is placed in a concentrated solution?
Water leaves the cell by
osmosis and
becomes flaccid.
The water is more concentrated inside the cell so water moves out to a lower water concentration
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40. The cell has become PLASMOLYSED
Osmosis in plant cells
If too much water leaves the cell, the membrane and cytoplasm split away from the cell wall.
The cell has become PLASMOLYSED
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41. Osmosis in plant cells A plant does not have a skeleton.
It relies on all of its cells being turgid in order to keep its structure.
This is called plant turgor.
Plan an experiment to investigate onion cell turgidity- use the words hypertonic, hypotonic and isotonic.
23 May 2019

42. Learning objectives Define active transport
Describe the role played by membrane bound proteins in active transport
Investigate water uptake by plants
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43. Active Transport
Define active transport as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
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44. Particles moving from low to a high concentration.
Active Transport
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.
Particles moving from low to a high concentration.
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45. Villus-Small Intestine
Active Transport
Active transport occurs in the roots of plants to move minerals into them against the concentration gradient and also in the epithelial cells in the villi of the small intestine of animals and in their kidneys during reabsorption it is a process that requires energy from ATP.
Plant minerals
Villus-Small Intestine
Kidneys
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46. Protein channels
The are small protein channels in the cell membrane that are important for active transport
23 May 2019

47. Water uptake by plants
Plan an experiment to Investigate the rate of water uptake by plants
23 May 2019