Post on 08-Apr-2018
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THE MOVEMENT OF SUBSTANCES
ACROSS THE PLASMAMEMBRANE.
ENTER
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STRUCTURE OF
PLASMA
MEMBRANE.
THE
PERMEABILITY
OF THE PLASMA
MEMBRANE.
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About the plasma membrane.
Plasma membrane, are composed mainly ofphoslipids and proteins.
Each phospholipid molecule consists of two
parts:. A polar head that gives it a hydrophilic property
[attrated to water], and
A pair ofnon-polar fatty acid tails that give ithydrophobic property [repelled by water].
Fluid mosaic model proposed by S.J Singer andG.L Nicholson.
View the
pictures and
video..
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G. L. Nicholson S. J. Singer
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The permeability of the plasma
membrane. A membrane is said to be impermeable.
Plasma membrane partially permeable or semi-
permeable.
The selective permeability of the plasmamembrane depends on the.
a) Selective barrier of the phospholipid bilayer, and
b) Specific transport proteins built into the
membrane. The size and polarity of molecules determine the
movement of these molecules across the plasma
membrane.
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The phospholipid bilayer is permeable to.
Non-polar molecules
[ lipids soluble].
Small, uncharged
molecules.
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The phospholipid bilayer is not permeable.
Charged ions.Polar molecules
[ lipid-insoluble].
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There are two ways in which molecules can moves across the
plasma membrane: passive transport and active transport.
Movement of substances across the plasma membrane.
Molecules transported
down the concentration
gradient .
Molecules transported
against the concentration
gradient.
Simple
diffusion. Osmosis.Facilitated
diffusion.
Passive transport Active transport
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Simple diffusion
Simple diffusion is net movement of molecules orions from a region of high concentration to aregion of lower concentration, that is, down theconcentration of a substance between two
regions. Molecules which move across the plasma
membrane by simple diffusion include:.
i. lipid-soluble molecules such as vitamins A, D, E,K.
ii. Small molecules such as water and
iii. Dissolved gases such as oxygen and carbondioxide.
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Osmosis
Osmosis is the diffusion of water
molecules across a semi-permeable
membrane.
Water molecules move across the
phospholipid bilayer and pore protein.
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Facilitated diffusion
Facilitated diffusion refers to the
movement of hydrophilic molecules or
ions across the plasma membrane with
the help of transport proteins.
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Active transport
Active transport is the movement of
molecules or ions from region of lower
concentration to a region of higher
concentration [against the concentration
gradient] across the plasma membrane.
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