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.
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
sodium ions, potassium
ions
ACTIVE TRANSPORT
IB question: Compare simple diffusion with facilitated diffusion as mechanisms to
transport solutes across membranes. [5]
IB question: Compare simple diffusion with facilitated diffusion as mechanisms to transport
solutes across membranes. [5]
Actual IB mark scheme
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
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 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 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]
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 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]
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.