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2.4.4: Define diffusion and osmosis Diffusion : The passive movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached. (Molecules still move after equilibrium is reached) . 2.4.4: Diffusion. 2.4.4: Define diffusion and osmosis.

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2.4.4: Define diffusion and osmosis


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  1. 2.4.4: Define diffusion and osmosis Diffusion: The passive movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached. (Molecules still move after equilibrium is reached)

  2. 2.4.4: Diffusion

  3. 2.4.4: Define diffusion and osmosis Osmosis: The passive net movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

  4. REMEMBER THIS SUMMARY Simple diffusion small and non-polar molecules e.g. oxygen PASSIVE TRANSPORT Facilitated diffusion large or polar or ions e.g. glucose, sodium ions ACTIVE TRANSPORT sodium ions, potassium ions

  5. IB question: Compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes. [5]

  6. IB question: Compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes. [5] Actual IB mark scheme

  7. 2.4.5: Passive Transport

  8. 2.4.6: Active Transport

  9. IB Question: Describe the process of active transport across membranes. [5]

  10. IB Question: Describe the process of active transport across membranes. [5] goes against concentration gradient / from low concentration to high concentration; requires hydrolysis of ATP / requires energy from ATP; proteins in membrane utilized; specificity of carriers; e.g. Na+-K+ pump / other suitable examples; may involve conformational change in carrier protein; moves ions / solutes; maintains chemical / electrical gradient; [5 max]

  11. IB question: Distinguish between active and passive movements of materials across plasma membranes,using named examples. [4]

  12. IB question: Distinguish between active and passive movements of materials across plasma membranes,using named examples. [4]

  13. 2.4.7: Vesicle Transport

  14. IB Question: Outline how vesicles are used to transport materials secreted by a cell. [6]

  15. IB Question: Outline how vesicles are used to transport materials secreted by a cell. [6] vesicles formed from rER transport proteins to Golgi apparatus; these vesicles fuse with membranes of Golgi apparatus; proteins are processed as they move through Golgi apparatus; (transport) vesicles bud off/leave Golgi apparatus; vesicles move through cytoplasm; (vesicles) fuse with plasma membrane; contents released to outside of cell / exocytosis; cells use vesicles to secrete substances such as hormones/digestive enzymes/other appropriate example; vesicles may contain cell products other than proteins; [6 max] Credit drawings which fully explain the points above.

  16. 2.4.8: Endo/Exocytosis

  17. IB question: Describe the process of endocytosis. [5]

  18. IB question: Describe the process of endocytosis. [5] endocytosis occurs when a membrane encloses a target particle; fluidity of membrane permits movement of membrane; membrane sinks inwardly/forms pit/invaginates to enclose particle; membrane seals back on itself / edges fuse; one membrane layer / two phospholipid layers enclose particle making vesicle; inner phospholipid layer of (original) membrane becomes outer phospholipid layer of vesicle membrane; outer phospholipid layer of (original) membrane becomes inner phospholipid layer of vesicle membrane; vesicle breaks away from membrane/moves into cytoplasm; changes in membrane shape require energy; specific example of endocytosis (e.g. pinocytosis, phagocytosis); [5 max] Accept any of the above points in an annotated diagram.

  19. IB question: Outline the various means of transfer of different types of molecules through the plasma membrane. [4]

  20. IB question: Outline the various means of transfer of different types of molecules through the plasma membrane. [4] diffusion is the movement of particles down a concentration gradient / higher to lower concentration / is passive; osmosis is passive transport / diffusion of water; osmosis is movement from lower solute concentration to higher / higher to lower water potential; facilitated diffusion involves channels (in membranes); active transport requires protein pumps/ATP/energy; active transport is movement against concentration gradient; correct reference to endocytosis/exocytosis/pinocytosis; [4 max]

  21. IB question: Explain the processes of active and passive transport that move materials across a membrane.[8]

  22. IB question: Explain the processes of active and passive transport that move materials across a membrane.[8] active transport: lower to higher (solute) concentration / against concentration gradient; uses energy / ATP; protein pumps/channels; gives a cell control; protein pumps transport specific substances; phagocytosis / pinocytosis; example of active transport; passive transport: diffusion; from high to low concentration; low to high; (but must be in context of random movement of particles) partial/selective permeability of membrane; example of simple diffusion; facilitated diffusion; protein channels; example of facilitated diffusion; [8 max] Award [4 max] for an account that deals with only one of active or passive transport.

  23. 2.4.5: Passive Transport

  24. 2.4.6: Active Transport

  25. IB Question: Describe the process of active transport across membranes. [5]

  26. IB Question: Describe the process of active transport across membranes. [5] goes against concentration gradient / from low concentration to high concentration; requires hydrolysis of ATP / requires energy from ATP; proteins in membrane utilized; specificity of carriers; e.g. Na+-K+ pump / other suitable examples; may involve conformational change in carrier protein; moves ions / solutes; maintains chemical / electrical gradient; [5 max]

  27. IB question: Distinguish between active and passive movements of materials across plasma membranes,usingnamed examples. [4]

  28. IB question: Distinguish between active and passive movements of materials across plasma membranes,usingnamed examples. [4]

  29. IB Question: Outline how vesicles are used to transport materials secreted by a cell. [6]

  30. IB Question: Outline how vesicles are used to transport materials secreted by a cell. [6] vesicles formed from rER transport proteins to Golgi apparatus; these vesicles fuse with membranes of Golgi apparatus; proteins are processed as they move through Golgi apparatus; (transport) vesicles bud off/leave Golgi apparatus; vesicles move through cytoplasm; (vesicles) fuse with plasma membrane; contents released to outside of cell / exocytosis; cells use vesicles to secrete substances such as hormones/digestive enzymes/other appropriate example; vesicles may contain cell products other than proteins; [6 max] Credit drawings which fully explain the points above.

  31. 2.4.8: Endo/Exocytosis

  32. IB question: Describe the process of endocytosis. [5]

  33. IB question: Describe the process of endocytosis. [5] endocytosis occurs when a membrane encloses a target particle; fluidity of membrane permits movement of membrane; membrane sinks inwardly/forms pit/invaginates to enclose particle; membrane seals back on itself / edges fuse; one membrane layer / two phospholipid layers enclose particle making vesicle; inner phospholipid layer of (original) membrane becomes outer phospholipid layer of vesicle membrane; outer phospholipid layer of (original) membrane becomes inner phospholipid layer of vesicle membrane; vesicle breaks away from membrane/moves into cytoplasm; changes in membrane shape require energy; specific example of endocytosis (e.g. pinocytosis, phagocytosis); [5 max] Accept any of the above points in an annotated diagram.

  34. IB Question: Outline, with an example, the process of exocytosis. [5] vesicles carry material to plasma membrane; vesicle fuses with membrane; (by joining of) phospholipidbilayers; aided by the fluidity of the membrane; material released/expelled from the cell; membrane flattens; name of example e.g. exocytosis of neurotransmitter / exocrine secretion/endocrine secretion / hormone secretion / release of cortical granules; outline of example: (in the presence of calcium), neurotransmitter vesicles release their contents into the synapse / hormones released from one cell have an effect on another cell etc.; [5 max] Accept these points if clearly made in an annotated diagram. [4 max] if no example given.

  35. IB Question: Outline, with an example, the process of exocytosis. [5]

  36. IB question: Outline the various means of transfer of different types of molecules through the plasma membrane. [4]

  37. IB question: Outline the various means of transfer of different types of molecules through the plasma membrane. [4] diffusion is the movement of particles down a concentration gradient / higher to lower concentration / is passive; osmosis is passive transport / diffusion of water; osmosis is movement from lower solute concentration to higher / higher to lower water potential; facilitated diffusion involves channels (in membranes); active transport requires protein pumps/ATP/energy; active transport is movement against concentration gradient; correct reference to endocytosis/exocytosis/pinocytosis; [4 max]

  38. IB question: Explain the processes of active and passive transport that move materials across a membrane.[8]

  39. IB question: Explain the processes of active and passive transport that move materials across a membrane.[8] active transport: lower to higher (solute) concentration / against concentration gradient; uses energy / ATP; protein pumps/channels; gives a cell control; protein pumps transport specific substances; phagocytosis / pinocytosis; example of active transport; passive transport: diffusion; from high to low concentration; low to high; (but must be in context of random movement of particles) partial/selective permeability of membrane; example of simple diffusion; facilitated diffusion; protein channels; example of facilitated diffusion; [8 max] Award [4 max] for an account that deals with only one of active or passive transport.