1. Starter Activity:
Answer the following question in your classwork jotter
What type of fibres are the cell walls of plants made of?
Name the small rings of DNA found in bacterial cells.
Name the process by which yeast cells reproduce.
What is the function of
a) ribosomes?
b) mitochondria?

2. Answers
Cellulose
Plasmids
Budding
a) protein synthesis
b) respiration

3. Transport across cell membranes
Key Area 2
Transport across cell membranes

4. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Be able to describe the structure of the cell membrane
Understand the terms passive and active transport
Understand the term diffusion and give examples of diffusion in cells
Understand the term osmosis and its effect on cells
Understand the idea of concentration gradient

5. The Function of the Cell Membrane
Twig Video Clip: The Cell Membrane
Whilst you are watching the video clip write down key words on a show me board.

6. Structure of the cell membrane
The cell membrane is very thin.
It is able to control the movement of materials into and out of cells.
When seen under an electron microscope, it can be seen to consist of a double layer.
Cytoplasm of cell
Cell membrane

7. Structure of the cell membrane
It has a double layer made of molecules called phospholipids.
Phospholipid molecules have a head and a tail end.
All the tails point inward and the heads point outwards.
Head end
Tails
Head end

8. Structure of the cell membrane
There are also proteins embedded in the membrane.
These proteins have various functions.
Some are involved in the transport of materials across the membrane.
Phospholipid double layer
proteins

9. Fluid mosaic model
The membrane is a very flexible structure which can move and change shape easily.
It is often described as a fluid mosaic model.
Fluid refers to the moving phospholipids and mosaic refers to the patchy arrangement of the proteins.

10. Homework task - Make a 3D cell membrane model
Your task is to make a 3D model of the cell membrane.
You can use any materials you can find at home, especially recycling materials.
Your model should show the proteins and the phospholipids with their head and tail ends.
The component parts should be labelled or there should be a key to identify them.
Examples of materials you could use include paper, cardboard, plastic bottle lids, plasticene, playdoh, straws, cotton buds, cocktail sticks, buttons, ribbons, fabric, lolly sticks, dry pasta, lego, stickle bricks, k’nex.
THE POSSIBILITIES ARE ENDLESS SO HAVE FUN!

11. Selectively permeable membrane
Permeability means the ability of a surface to allow molecules to pass through it.
The cell membrane is usually described as selectively permeable.
This means that it allows some molecules to move through it easily, but others move more slowly, and some cannot move across it at all.

12. Visking tubing
Visking tubing is a selectively permeable material that acts like a cell membrane.
We can use it to demonstrate which molecules are able to pass through the membrane, and which are not.
Your teacher will show you how to use the visking tubing in an experiment.

13. Visking tubing experiment
Water
Visking tubing bag
Starch and glucose solution
Test water for starch and glucose after 20 minutes

14. Visking tubing experiment
Soften a length of visking tubing under running water until you can open it up.
Tie a firm knot in one end.
Add equal volumes of starch and glucose solutions using droppers.
Tie a firm knot in the other end. Cut off any excess tubing to leave 1cm tails.
Wash the bag thoroughly under running water.
Place bag in a test tube, cover with water and leave for 20 minutes. Remove the bag.
Transfer a drop of the water to a spotting tile and test for starch using iodine.
Test the remaining water for glucose by adding Benedicts solution and heating to 80°C for 5 minutes.

15. Visking tubing experiment
Results:
Colour change observed
Result of test – positive or negative
Starch test (iodine)
Glucose test
(Benedicts)
Conclusion : The ______was able to pass through the visking tubing but the _______was not. This is because starch has ________ molecules but glucose has ________molecules.

16. Selectively Permeable Membranes
Cell membranes allow small molecules like glucose, oxygen and water to pass through them freely.
This is because the membrane has tiny holes in it called pores that make it permeable. Large molecules like starch are unable to pass through. 16

17. Selectively Permeable Membranes
Pores in the membrane are small, so only small molecules such as glucose, water, oxygen and carbon dioxide can get through.
Large molecules such as starch cannot pass through.
Selectively permeable membranes allow certain molecules to pass through but not others.
nucleus
selectively permeable membrane
cytoplasm 17

18. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Be able to describe the structure of the cell membrane
Understand the terms passive and active transport
Understand the term diffusion and give examples of diffusion in cells
Understand the term osmosis and its effect on cells
Understand the idea of concentration gradient

19. Starter

20. Starter C

21. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the terms passive and active transport
Understand the term diffusion and give examples of diffusion in cells

22. Passive transport
passive transport is the movement of a substance across a cell membrane down a concentration gradient
It does not require energy.
The two types of passive transport are:
Diffusion
Osmosis

23. Diffusion
Diffusion is the movement of molecules in a liquid or gas from high to low concentration until they are evenly spread out.
Diffusion moves down a concentration gradient.
Diffusion clip 23

25. Diffusion in liquids
Diffusion in liquids can be seen by adding dye to a beaker of water.
Add dye to one side only
Water
Do not shake or stir. Leave for 20 minutes.

26. Diffusion in liquids
Red dye in water
Red dye molecules and water molecules have moved until they are evenly spread – this is DIFFUSION.

27. Direction of diffusion
Diffusion always occurs from high concentration of a molecule to low concentration of that molecule.

28. Concentration Gradient
The difference in concentration of two solutions is called a concentration gradient.
In diffusion, molecules will always move down the concentration gradient from high concentration to low concentration. 28

29. Concentration Gradient
Like a ball on a slope, molecules diffuse down a concentration gradient from high to low.
high ground
gradient (slope)
low ground
ball
ball rolls down gradient
ball stops 29

30. Concentration Gradient
A concentration gradient exists when there is a difference in concentration from one area to another.
Molecules move down a concentration gradient from high to lower concentration. The molecules will stop moving when the two concentrations are equal. 30

31. Cells and diffusion
Many substances can enter or leave cells by diffusion.
This happens across the cell membrane.
Animal cells take in glucose, oxygen and amino acids by diffusion.
Carbon dioxide and waste materials leave animal cells by diffusion.

32. Diffusion in an animal cell
Glucose
Carbon dioxide
Oxygen
Waste
Amino acids

33. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the terms passive and active transport
Understand the term diffusion and give examples of diffusion in cells

34. Starter

35. Starter
Diffusion
Waste/carbon dioxide
Cell membrane

36. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis and its effect on cells
Understand the idea of concentration gradient

37. Osmosis
Water can also diffuse into and out of cells across the cell membrane.
Osmosis is the special diffusion of water from an area of high concentration to an area of low concentration through a selectively permeable membrane.
Low water concentration
High water concentration
Twig Video Clip - Osmosis 37

38. Visking tubing
Visking tubing is a selectively permeable material that can be used to show the effect of osmosis on cells.
The visking tubing behaves like a cell membrane, so we can use it to make model cells.

39. Osmosis experiment A B Visking tubing bag 10% sugar solution water
TEACHER DEMONSTRATION
Osmosis experiment A B
Visking tubing bag
10% sugar solution
water
Boiling tube
Wash and dry bags when filled.
Weigh both bags.
Place in test tubes for 20 minutes then dry and reweigh.

40. Results A B Mass of bag and contents at start (g)
Mass of bag and contents after 20 minutes (g)
Difference in mass (g)

41. Conclusion
Bag A increased/decreased in mass. This was because water moved in/out by osmosis.
Bag B increased/decreased in mass. This was because water moved in/out by osmosis.
Water always moves from ________ water concentration to ______ water concentration.

42. Answer the following questions in sentences:
Why was the visking tubing bag dried in a paper towel before being weighed?
Why was visking tubing used in this experiment? What property does it have that makes it a good model cell?
What would happen to an onion cell placed in pure water?
What would happen to a cheek cell placed in 10% sucrose solution?

43. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis and its effect on cells
Understand the idea of concentration gradient

44. Starter

45. Starter C

46. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis Understand the effect of osmosis on plant cells

47. Osmotic Effect On Cells
Water concentrations
If we think about solutions in terms of their water concentrations, it is easier to recognise which direction water molecules will flow in.
A dilute sugar solution will have a high concentration of water, whereas a concentrated sugar solution will have a lower water concentration. 47

48. Concentrated Sugar Solution
Dilute Sugar Solution
Low water concentration
High sugar concentration
High water concentration
Low sugar concentration 48

49. Direction of water movement
Water Concentrations
Cell in pure water
Direction of water movement
H2O concentration >
cell
The surrounding solution has a higher water concentration than the water concentration within the cell, so water enters by osmosis. 49

50. Water Concentrations
Cell in concentrated salt solution
H2O concentration <
cell
The surrounding solution has a lower water concentration than the water concentration within the cell, so water leaves the cell by osmosis. 50

51. Water Concentrations
Cell in solution with equal concentration to cell contents.
H2O concentration =
cell
The surrounding solution has a water concentration that is equal to the water concentration within the cell, so there is no gain or loss of water by osmosis. 51

52. Investigating osmosis in potato tissue
Copy the title and the aim from the instruction card.
Prepare a results table.
Set up the experiment by following the instructions on the card.

53. Results
Conclusion
Evaluation
Bathing solution
Initial mass (g)
Final mass (g)
% Change in mass
Water
Strong sucrose solution

54. Plant Cells and Osmosis
Pure water: there is more water outside of the cell than inside, therefore water will move into the cell by osmosis. This causes the cell to swell and become turgid.
Strong salt solution: there is more water inside the cell than outside, therefore water will move out of the cell by osmosis. This causes the cell to become softer or flaccid.
Cell in pure water
Cell in strong salt solution 54

55. Plant Cells and Osmosis

56. Plant Cells and Osmosis
Cell in pure water - turgid
Normal cell
Cell in strong salt solution - plasmolysed

57. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis Understand the effect of osmosis on plant cells

58. Starter

59. Starter A

60. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis Understand the effect of osmosis on animal cells

61. Viewing plasmolysed cells
In this practical, you will expose onion cells to a solution of salt to observe plasmolysis. You will also prepare cells in water for comparison (as a control experiment).
You will view the cells under the microscope and make drawings of what you see.
You will need a pencil and a circular object (eg beaker) to draw round.
Follow the instructions on the card provided.

62. Plasmolysis in onion cells
The photo shows onion cells which have been bathed in strong salt solution and have become plasmolysed.
Notice how the cytoplasm and cell membrane have shrunk inwards away from the cell wall.
cell wall
cell membrane
nucleus
cytoplasm

63. Osmosis in red cabbage cells Your task in this experiment is to identify liquids A and B by looking at the results.
Label two boiling tubes A and B.
Half fill tube A with liquid A and tube B with liquid B.
Cut 10 discs from red cabbage using a cork borer.
Wash the leaf discs in a small beaker of water and dry them gently.
Add 5 discs to each test tube.
Leave for 20 minutes and observe any colour change in the liquids.

64. Osmosis in red cabbage cells
Results:
Test tube A
Test tube B
Appearance of liquid
Conclusion:
Which test tube contained strong sucrose solution?
How do you know this?
Which test tube contained water?

65. Animal Cells & Osmosis
The effects of osmosis on animal cells are totally different to plant cells because animal cell structures are different.
Animals cells do not have:
Cell walls
Vacuoles 65

66. Animal Cells & Osmosis
Red blood cells (RBCs) float in a liquid called plasma which is the same water concentration as the cells.
RBCs in plasma do not change size because the water has no concentration gradient to follow.
RBCs will change if there is a concentration gradient for water to follow. 66

67. Animal Cells & Osmosis Normal red blood cell
RBC in strong salt solution
RBC in equal concentration solution
RBC in pure water
Cell loses water by osmosis and shrinks.
No net osmosis, cell stays the same.
Cell takes in water by osmosis, swells and eventually bursts. 67

68. Osmosis in eggs
Your teacher will show you a demonstration experiment involving eggs placed in different solutions.
Write a description of this experiment in your notebook. Include the following:
Title
Diagram
Method
Result
Conclusion

69. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term osmosis Understand the effect of osmosis on animal cells

70. Starter

71. Starter
Turgid

72. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term active transport and its effect on cells
Understand the idea of concentration gradient

73. Passive transport
Diffusion and osmosis are examples of passive transport.
This always involves movement of molecules down a concentration gradient.
Passive transport does not need any energy input.

74. Active transport
Some molecules and ions are moved across the membrane by active transport.
This involves movement of molecules and ions against a concentration gradient.
Active transport does need energy input.
Membrane proteins are involved in this process.
Transport across cell membranes (Glow)

75. Active transport

76. The sodium potassium pump
This is an example of active transport which occurs in nerve cells.
Sodium ions are pumped out of cells against the concentration gradient.
Potassium ions are pumped into cells against the concentration gradient.
OUTSIDE THE CELL
Sodium pumped out
CELL MEMBRANE
Membrane proteins
Potassium pumped in
INSIDE THE CELL

77. Active transport in cells
When a cell is alive, the membrane can use active transport to make sure that suitable molecules are allowed to build up in the cell, and unsuitable or harmful molecules are kept out of the cell.

78. Practical application of this idea
You will probably have had antibiotics at some time for an infection.
Many antibiotics work by destroying the membranes of live bacteria in your body.
The damaged membranes allow vital nutrients to escape and poisonous substances to enter and kill the bacterial cells.

79. Transport across cell membranes
Learning Intention:
Investigate the cell membrane and the movement of molecules across it
Success Criteria:
Understand the term active transport and its effect on cells
Understand the idea of concentration gradient