2.4 Cell Membranes Presentation IBDP SL Biology

7/27/2019 2.4 Cell Membranes Presentation IBDP SL Biology

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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_UJcfBc


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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=n8ZvK0r9HIY


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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.html


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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html


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Still confused? This might help
http://goanimate4schools.com/public_movie/0ZVm9NFo0EC8


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Passive Transport
http://www.youtube.com/watch?v=s0p1ztrbXPY


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http://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swfhttp://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swf


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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.html


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2.4.6 Active Transport
http://www.youtube.com/watch?v=STzOiRqzzL4


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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.swf


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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.htm


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2.4.7 Role of vesicles
http://www.sumanasinc.com/webcontent/animations/content/vesiclebudding.html


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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%20Exocytosis


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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%20Exocytosis


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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.html


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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html


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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

2.4 Cell Membranes Presentation IBDP SL Biology

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