2.4.4: define diffusion and osmosis

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

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.

Simple diffusion

REMEMBER THIS SUMMARY

small and non-polar molecules e.g. oxygen

large or polar or ions e.g. glucose, sodium ions

Facilitated diffusion

ACTIVE TRANSPORT

PASSIVETRANSPORT

sodium ions, potassium ions

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

Actual IB mark scheme

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

2.4.5: Passive Transport

2.4.6: Active Transport

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

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]

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

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

2.4.7: Vesicle Transport

2.4.8: Endo/Exocytosis

Transport across membranes summary

Transport acrossmembrane

Passive

Active

Simple diffusion

Facilitated diffusion

Active transport

Exocytosis

Endocytosis

Phagocytosis

Pinocytosis

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

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.

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

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.

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

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 tolower concentration / is passive;osmosis is passive transport / diffusion of water;osmosis is movement from lower solute concentration to higher / higher to lowerwater 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]

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

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.

2.4.5: Passive Transport

2.4.6: Active Transport

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

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]

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

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

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

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.

2.4.8: Endo/Exocytosis

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

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.

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

vesicles carry material to plasma membrane; vesicle fuses with membrane; (by joining of) phospholipid bilayers; 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.

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

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

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 tolower concentration / is passive;osmosis is passive transport / diffusion of water;osmosis is movement from lower solute concentration to higher / higher to lowerwater 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]

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

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.