Starter Activity: Answer the following question in your classwork jotter

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. 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: 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.

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. cytoplasm nucleus selectively permeable membrane

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

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.

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

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.

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

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. 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

41. Conclusion • Bag A increased/decreased in mass. This was because water moved in/outby 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

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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.

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

49. 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.

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.