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2.4 Cell Membranes
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Assessment Statements2.4.1 Draw and label a diagram to show the structure of membranes.
2.4.2 Explain how the hydrophobic and hydrophilic properties of
phospholipids help to maintain the structure of the cell
membranes.
2.4.3 List the functions of membrane proteins.
2.4.4 Define diffusion and osmosis.
2.4.5 Explain passive transport across membranes by simplediffusion and facilitated diffusion.
2.4.6 Explain the role of protein pumps and ATP in active transport
across membranes.
2.4.7 Explain how vesicles are used to transport materials within acell between the rough endoplasmic reticulum , Golgi apparatus
and plasma membrane.
2.4.8 Describe how the fluidity of the membrane allows it to change
shape, break and reform during endocytosis and exocytosis.
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u osa c o e o eMembranes
http://www.youtube.com/watch?v=Qqsf_UJcfBc7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Fluid
A continuous, amorphous substance
whose molecules move freely past one
another and that has the tendency toassume the shape of its container; a
liquid or gas.
MosaicA picture or decorative design made by
setting small colored pieces, as of
stone or tile, into a surface.
What does the fluid mosaic
model tell us about cell
membranes?
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2.4.1 Draw and label the cell
membrane
http://www.youtube.com/watch?v=n8ZvK0r9HIY7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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a. glycoprotein b. glycolipid
c. carbohydrate
e. phospholipid
bilayer
i. integral protein
h. cholesterolg. peripheral protein
d. fatty acid tails
(hydrophobic)
j. cytoskeleton
f. phosphate heads
(hydrophilic)
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Hydrophi l ic
Polar
Water loving
Hydrophobic
Non polarWater fearing
2.4.2 Properties of Phospholipids
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The heads have a large
charged phosphate
group - hydrophi l ic
Tails are non
polar uncharged
and hydrophob ic
Heads face the watery
environments inside and
outside the cell
Tails face into the
bilayer creating a
barrier between
internal and externalenvironments
Phospholipids are attracted to
each other due to their charges.
This gives the membrane
Cholesterol increases
stability and maintains
fluidity
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2.4.3 Membrane Proteins
Integral versus peripheral
Integral - span from one side
of the bilayer to the other
Peripheral -sit on the
surface of the membrane
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Glycoproteins
Carbohydrate chains
(oligosaccharides)
attached to proteinsembedded in the
membrane
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Channel Proteins
Span the membrane from one side to the other.Allow the movement of large or charged molecules
across the membranes.
Pores, carrier proteins and membrane pumps.
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Receptor Proteins
Proteins which detect chemicals, e.g.
hormones which trigger a change in the cell.
Also includes recognition proteins which are
involved in immunity.
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Enzymes
Enzymes which are
integral in the membrane
e.g. ATP synthase
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Electron carriers
Involved in oxidation and reduction reactionse.g. in photosynthesis and respiration as part of
the electron transport chain
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2.4.4 Diffusion and Osmosis
Diffusion
Osmosis
the net movement of molecules from a region of
their higher concentration to a region of their
lower concentration down a concentration
gradient, as a result of their random movement
the diffusion of water molecules from a region
of their higher concentration to a region of their
lower concentration, through a partiallypermeable membrane
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Diffusion
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Try this!
http://esminfo.prenhall.com/science/BiologyArchive/lectureanimations/closerlook/diffusion.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Still confused? This might help
http://goanimate4schools.com/public_movie/0ZVm9NFo0EC87/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Passive Transport
http://www.youtube.com/watch?v=s0p1ztrbXPY7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swfhttp://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swf7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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2.4.5 Passive Transport
Requires no energy
Molecules are moving randomly (kinetic energy)
Includes diffusion, facilitated diffusion and
osmosis
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Simple diffusion
High
concentration
Low
concentration
e.g. O2 and CO2
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Some molecules are so smal lthat they pass
through the membrane with little resistance
e.g. oxygenand carbon diox ide
Lip idmolecules (even though very large)
pass through membranes easily as they
are non polar.
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Facilitated diffusion
Large, charged molecules move passively through the
membrane via channel pro teins
These proteins have large
globular struc turesand
complex 3d-shapes
The shapes provide a
channel through the
middle of the protein, the
'pore'
The channel 'shields' the diffusing molecule from the non-
charged/ hydrophobic/ non-polar regions of the membrane.
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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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2.4.6 Active Transport
http://www.youtube.com/watch?v=STzOiRqzzL47/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Requires energy in the form ofATP
Carries large, chargedsubstances across the
membranee.g. Na+and K+ ions
Againstthe concentration gradient
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http://www.northland.cc.mn.us/biology/biology1111/animations/active1.swfhttp://www.northland.cc.mn.us/biology/biology1111/animations/active1.swf7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://www.wiley.com/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htmhttp://www.wiley.com/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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2.4.7 Role of vesicles
http://www.sumanasinc.com/webcontent/animations/content/vesiclebudding.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Endomembrane system
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Consists of:
Nuclear membrane
ER
Golgi apparatus
Vesicles
VacuoleLysosomes
Cell membrane
Function
Protein synthesis, modification and transport
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2.4.8 Endocytosis and Exocytosis
Bulktransport
Requires energy(ATP)
Involves formation ofvesicles
Endocy tos is -materials entering the cell
Exocytos is- materials exiting the cell
e.g secret ionofhormonesand digest ive
enzymes, phagocytos isin white blood cells
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Endocytosis
Exocytosis
Invagination of cell
membrane
These processes are possible because cell
membranes are fluid and can move in order to fold
around materials
Vesicle
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Types of Endocytosis
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Endocytosis
http://www.youtube.com/watch?v=4gLtk8Yc1Zchttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology
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Review Question
Which of the following is not a function
performed by a membrane protein?
A. Hormone binding sites
B. Cell adhesion
C. Enzyme synthesis
D. Pumps for active transport
(Total 1 mark)
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Review Question
Which of the following is not a function
performed by a membrane protein?
A. Hormone binding sites
B. Cell adhesion
C. Enzyme synthesis
D. Pumps for active transport
(Total 1 mark)
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Review Question
(a) Define osmosis.(1)
(b) Outline how transport occurs across
membranes by facilitated diffusion.(2)
(c) Explain how the properties of phospholipids
help to maintain the structure of cell membranes
(3)
(Total 6 marks)
( ) ( i i ) th i t f t / l t l l f
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(a) (osmosis is) the passive movement of water / solvent molecules from a
more dilute solution / region of lower solute concentration to a more
concentrated solution / region of higher solute concentration through
a partially permeable membrane
(b) facilitated diffusion is a form of passive transport / molecules move from
a
region of higher concentration to a region of lower concentration / down a
diffusion gradient;
requires specific protein channels in plasma membrane;
(c) phospholipds have hydrophilic and hydrophobic regions;
hydrophilic heads attracted to water and hydrophobic / fatty acid tails repelled
by / not attracted to water;
phospholipd bilayer forms with heads in contact with water on both sides of
membrane / with environment and cytoplasm;
hydrophobic tails found in centre (of bilayer) away from water;
stability to membrane brought about by attraction between hydrophobic
tails / between hydrophilic heads and water;
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(b) Outline how vesicles are used to transport
materials secreted by a cell. (6)
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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/digestiveenzymes/other appropriate example;
vesicles may contain cell products other than proteins;
Credit drawings which fully explain the points above.
6 max
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(a) Draw a labelled diagram to show the
structure of a membrane (5)
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Award[1]for each of the following clearly drawn and
correctly labelled.
phospholipid bilayerdouble row of opposing
phospholipids, tails to inside;
phospholipid with head and two tails;
hydrophilic/phosphate/polar (heads) and
hydrophobic/hydrocarbon/fatty
acid/non-polar (tails) labelled;
integral protein embedded in the phospholipid bilayer;
protein channel integral protein showing clear
channel/pore;peripheral proteinon the surface;
glycoproteinwith carbohydrate attached on one side;
cholesterolshown embedded in bilayer;
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(b) Describe the process of endocytosis.(5)
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(b) 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);
Accept any of the above points in an annotated diagram. 5 max