Biology 3A – membranes

1. Biology 3A – membranes

2. Cells exchange matter and energy Processes: In: Out:

3. Cells exchange matter and energy In: Oxygen Nutrients eg glucose (carbon dioxide and light energy in plants) Water Ions Out: Carbon dioxide Wastes eg urea (oxygen in plants) Water Ions Heat energy Processes: Respiration Synthesis Growth Division Photosynthesis (in plants)

4. Exchange of material Occurs at the cell membrane Involves the intake of essential materials eg nutrients and oxygen and the removal of unwanted materials eg wastes The processes involved include diffusion, osmosis and active transport

5. Cell membranes Sketch a typical cell membrane according to the Fluid Mosaic model Describe the roles of: • Phospholipids • Proteins • Carbohydrates

6. Cells C A Sketch a typical cell membrane according to the Fluid Mosaic model . B Describe the roles of: Phospholipids = A – waterproof, flexible layer, that lets in small particles Proteins = B – provides channels for larger particles (facilitated diffusions), acts as pumps (active transport), acts as receptor sites Carbohydrates = C -acts as receptor sites

7. Structure of the cell membrane Fluid mosaic model Describe the roles of: • Phospholipids Waterproof barrier, acts as a bubble, main constituent • Proteins Act as carriers, receptor sites, antigens, channels • Carbohydrates Act as receptor sites, antigens

8. Evidence for membrane structure • Biochemical analysis • Electron microscopy • Fluorescent and radioactive markers Fluorescent markers added to cell membrane Markers have moved around the entire membrane Markers found on other membranes within cell Cells merged so markers on 1 side

9. Exchange of material Small particles eg water, ions can pass through the gaps between the phospholipids Larger molecules pass through channels in the proteins or are carried by special proteins

10. Terminology Mixture of solvent and solute Solution Solute Solvent Permeable Differentially permeable Hypotonic Hypertonic Isotonic Thing added to solvent Liquid to which solute is added Allows substances to move through Allows some substances to move through, but not others Less concentrated (dilute) More concentrated Concentrations are equal

11. Movement through membranes

12. Diffusion Draw a diagram to show how materials are exchanged by diffusion

13. Movement of particles - diffusion Occurs without energy Particles will move from higher concentrations to lower concentrations

14. Diffusion through membranes Membranes are differentially permeable Permeable substances (eg small particles) Impermeable substances (eg large particles) Movement is Energy

15. Diffusion through membranes Membranes are differentially permeable Permeable substances (eg small particles) Impermeable substances (eg large particles) Movement is Energy Move through Can’t move through From areas of high concentration to areas of low concentration Is not needed

16. Facilitated diffusion Allows larger or less permeable substances to cross Involves channel proteins Energy is not needed

17. Osmosis Draw a diagram to show how materials are exchanged by osmosis

18. Osmosis Movement of water This occurs from areas of high water concentration (low concentration of solute) to areas of low water concentration (high concentration of solute)

19. Concentration gradient This refers to the difference in concentration across membranes The steeper the gradient, the greater the movement Osmotic pressure refers to the pull of water due to concentration gradients

20. Active transport Draw a diagram to show how materials are exchanged by active transport

21. Active transport Movement against a concentration gradient. Energy is needed

22. Ion pumps Involves special proteins that act as pumps Allows cells to maintain ion concentrations that are very different from the external environment Energy is used

23. Endocytosis Movement due to folding of membrane and bringing in the trapped substances Energy is needed Phagocytosis – solid substances trapped Pinocytosis – liquids are trapped

24. Exocytosis Movement due to vacuoles moving to membrane and attaching to release contents Energy needed

25. Exchange of material Show the movements of water and ions that would occur in both these cases Distilled water Sea water

26. Exchange of material Show the movements of water and ions that would occur in both these cases Distilled water Sea water Water moves in Ions move out Water moves out Ions move in

27. Determining the components of the cell membrane Beetroot lab water Distilled water Salt water acid base detergent

28. Beetroot experiment • What hypothesis is being tested? • What is the control? • What is the independent variable? • What is the dependent variable • What variables are controlled? • How will this tell you about the components of the cell membrane?

29. Size and surface area As size increases what happens to surface area to volume ratio? Why is this important?

30. Size and surface area As size increases what happens to surface area to volume ratio? SA:Vol decreases Why is this important? Exchange occurs at surfaces – the larger the SA:Vol, the more exchange will occur

31. Shape and surface area What happens if cells change shape? 2x 2x2 4x2x1 1x1x8

32. Shape and surface area What happens if cells change shape? – alters surface area 2x 2x2 4x2x1 1x1x8

33. How cells increase their surface area • Size • Shape • Folding • Cell extensions pseudopods microvilli