Osmosis, Diffusion, Passive Diffusion, Facilitated Diffusion

1. TRANSPOR
T
MECHANIS
M
By: Mrs. Kalaivani Sathish

2. INTRODUCTION
• Transport of various substances across a
plasma membrane may occur by several
mechanisms, which includes, diffusion
(passive diffusion), facilitated diffusion and
active transport.
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3. DIFFUSION
• Diffusion of a substance may occur
either passively (called passive
diffusion) or may required some
carrier protein, which facilitates
diffusion (Called Facilitated diffusion)
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4. PASSIVE
DIFFUSION
• Diffusion or passive diffusion refers to a
process in which a solute moves down an
electro chemical gradient from one side of
the membrane to the other.
• It is an energy independent process, which
takes place by the dissipating its free energy
stored in the gradient.
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5. OSMOSIS
• Water moves readily through a semi
permeable membrane from a region of
lower solute concentration to a region
of higher solute concentration. This
process is called as osmosis.
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6. OSMOSIS
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7. A hypertonic solution is a particular type
of solution that has a greater concentration
of solutes on the outside of a cell when
compared with the inside of a cell.
A hypotonic solution is any solution that has a
lower osmotic pressure than
another solution.
When the cell is placed into a hypotonic
solution it rapidly gains water by osmosis
and swells, converselywhen the cell is placed
in the hypertonic solution, it losses water by
osmosis and shrinks.
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8. Once the internal solute concentration
becomes equal to the external solute
concentration, internal and external fluids
are said to be isotonic or iso osmotic.
At this stage no movement of water into or
out of the cells occur.
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9. Facilitated
Diffusion
• Large polar molecules such as glucose and amino acids,
cannot diffuse across the phospholipid bilayer. Also ions such
as Na+
or Cl-
cannot pass.
• These molecules pass through protein channels instead.
Diffusion through these channels is called FACILITATED
DIFFUSION.
• Movement of molecules is still PASSIVE just like ordinary
diffusion, the only difference is, the molecules go through a
protein channel instead of passing between the phospholipids.
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11. Active Transport
• To move substances against a concentration
or electrochemical gradient, a cell must use
energy. Active transport mechanisms do
just this, expending energy (often in the
form of ATP) to maintain the right
concentrations of ions and molecules in
living cells
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12. 2 Types of Active
Transport Mechanism
• Primary Active Transport – these are
found in all living organisms and require an
energy source such as ATP for the
translocation of the cations.
• These transporters since utilize ATP are
also referred to as ATPases.
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13. • Secondary Active Transport – they
utilize a secondary source of energy such as
trans – membrane electro chemical
gradient of either Na+ or H + to translocate
small organic molecules e.g. Glucose and
Amino Acids etc.
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