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Movement of substances acrossthe plasma membrane
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(A)
(B)
(D)
(E)
(C)
(F)
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Structure of the plasma membrane
• composed mainly of ▫ phospholipids and
▫ proteins
• The movement of substances
in and out of a cell occursthe plasma membrane
• The fluid-mosaic model
▫ proposed that
membrane proteins aredispersed throughout and inserted into the
phospholipid bilayer
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• Phospholipid molecule▫ polar head - hydrophilic
property and
▫ a pair of non-polar tails-
• Phospholipid bilayer acts as
▫ a barrier
▫ isolates the two sides of the membranes
• Cholesterol molecules▫ stabilize the structure of
the plasma membrane
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• Pore protein▫ protein molecule that
forms a channel or a pore
• Carrier protein
▫ protein molecule that acts as a carrier• glycoproteins
▫ membrane proteinsthat have
carbohydratesattached to them• The phospholipid
bilayer, proteins andother components
▫ not rigid or static
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• Selective Permeable / Semi Permeable
• Carrier Protein
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The permeability of the plasma
membrane• Selectively permeable/semi-permeable
▫ some substances can move across the membrane
• Factors that determine permeability
▫ the size and
▫ polarity
• pass through the phospholipids bilayer freely ▫ Lipid soluble molecules
▫ Non Polar Molecules
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• hydrophobic tails - prevent polar molecules topass through it,▫ but because of the small molecular size of
water - it can slide between the phospholipids bilayer / move through the pores
• Pore proteins▫ allow small water-soluble molecules and ions
• Carrier proteins▫ Used by large water-soluble molecules such as
amino acids and glucose to pass through theplasma membrane
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The movement of substances across the
plasma membrane : passive transport
• Simple diffusion▫ Net movement of
articles (molecules )
▫ from of higherconcentration to aregion of lowerconcentration.
• Expenditure of energy -not required• continue until -
dynamic equilibrium is
reached
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• Example of processin living organismsis the diffusion of
oxygen from thealveolus into theadjacent blood
capillaries
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Osmosis
• Net movement of water molecules
• from a region of higher concentration of water
water molecules
• through a partially permeable membrane.
• Eg.
▫ reabsorption of water molecules from thenephron into the blood capillaries
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Facilitated diffusion
• The passivemovement of molecules or ions
gradient.• involves
▫ pore proteins(channel proteins) or
▫ carrier proteins
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• The particularmolecules combinewith the specific active
site of the carrier protein.
• The carrier proteinchan es its sha e
• After assisting themovement of moleculesto the other side of theplasma membrane, it isfree to bind with othermolecules
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• Example- thereabsorption of glucose and amino
acids from the villiinto the bloodcapillaries
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• Active Transport
• Definition :
• Energy Involve
• Concentration Gradient :
• Name of energy :
• Source :
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The movement of substances across the
plasma membrane : active transport
• The movement of substances (ions) acrossa cell membrane
• from a re ion of lower
concentration to aregion of higherconcentration,
• against a concentration
gradient.▫ requires expenditure of
energy from ATP
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• particularmolecules/ionscombine with▫ specific active site of
the carrier protein.
• carrier protein changeits shape▫ when the phosphate
group from ATPmolecules binds to it toa ow t e mo ecu es/ions to pass throughto the other side of theplasma membrane.
• After assisting tomovement of molecules
to the other side of theplasma membrane,▫ it is free to bind with
other molecules
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• Active transport▫ result in the
accumulation of orelimination of molecules
▫ Carrier proteins are oftencalled pumps as they actlike water pumps whichuse energy to move wateragainst the gravity
• Example-
▫ the absorption of mineralsalts into the hair roots
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• Isotonic :
• Hypotonic :
• Hypertonic :
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The movement of substances across
the plasma membrane• Movement of substances across the plasma
membrane is necessary :a To su l nutrients to the cell
b) To allow exchange of respiratory gasesc) To remove waste products• Substances may move through a membrane by
simple diffusion, facillitated diffusion, osmosisand active transport
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Movement of substances across theplasma membrane in everyday life
• Isotonic solution – asolution that has the sameconcentration of solutes asanother solution
–
solution that has a lowertotal concentration of solutes than anothersolution
• Hypertonic solution – a
solution that has a highertotal concentration of solutes than anothersolution
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Define
• Crenation
• Haemolysis
• Turgid
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Animal and plant cells in an isotonicsolution
• Water moleculesmove into and out of a cell at the same
rate and the cellretains its normalshape (normal
concave disc shapered blood cell andplant cells)
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Animal and plant cells in anhypertonic solution
• Water leaves a cell by osmosis causingthe cell to shrink loose water . The
cell shrivel and theplasma membranecrinkles up of red
blood cell known as
crenation and inplant known asplasmolysis
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Animal and plant cells in anhypotonic solution
• Water enters a cell by osmosis causingthe cell to swell. The
bursting of red blood cell is knownas haemolysis and in
plant known asturgid
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Generate ionic
Gradients essential
For muscular and
Nervous activities
Secrete useful
substances
To remove toxic
substances
Maintain a suitable pH
And ionic concentrationInside the cell
Obtain certain
Food supplies
across membrane