Crossing the Membrane

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Crossing the Membrane
Cell Membrane Structure Transport
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Shipping and Receiving
All cells need to exchange substances like food,
water, and nutrients with their environment
Cell membranes accomplish this exchange through
cell transport!
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The Fluid Mosaic Model
Why is the membranes structure described as a
fluid mosaic?

• Membranes are fluid and have the consistency of
  vegetable oil
• The lipids proteins are always in motion
• Proteins form patterns or mosaics

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Membrane Structure and Properties

• Cell Membrane is composed of
• Phospholipid bilayer forms the basic unit of
  the cell membrane
• Proteins help transport large molecules through
  the membrane
• Carbohydrates help cells send and receive
  chemical messages

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Phospholipid Bilayer
Phosphate heads interact with water Hydrophilic
Lipid tails repel water Hydrophobic
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• 2 Main Types of Cell Transport
• Passive Transport NO energy required
• Active Transport NEEDS energy

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Passive Transport
Passive Transport Movement of materials across
the membrane that does not require energy
Diffusion
3 Types
Osmosis
Facilitated Diffusion
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Diffusion
Hi to the Low YO!
Diffusion is the movement of molecules from an
area of high concentration to an area of lower
concentration until they are evenly spread out
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Concentration Gradient and Permeability affect
whether diffusion occurs across a membrane

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Concentration Gradient the difference between
the amount of a particular substance in one area
and the amount in an adjacent area
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Permeability is the ability of a substance to
pass through the membrane

• Impermeable Cannot pass
• Selectively permeable or Semi-permeable and only
  allow certain molecules to pass

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Osmosis
Osmosis is the diffusion of water molecules
through a selectively permeable membrane
Water will continue to diffuse/move until there
is an equal concentration of molecules inside and
outside the cell.
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Hypertonic Solutions

• Solute concentration outside of the cell is
  higher than the solute concentration inside the
  cell
• Water moves OUT of the cell

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Hypotonic Solutions

• Solute concentration outside of the cell is lower
  than the solute concentration inside the cell
• Water moves INTO the cell

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Isotonic Solution

• Solute concentration in the solution is equal to
  the solute concentration in the cell
• Water moves equally in and out of the cell

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Which way will the water move?
On the left side, more of the space is occupied
by solutes than by water
Water will move To the left!

90 H2O
60 H2O
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Which way will the water move?
Water will move into the Cell
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What type of solution is this cell in?
Hypotonic Solution
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Which way will the water move?
Water will move Into and out of the cell
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What type of solution is this cell in?
The cell is in a Isotonic Solution
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Which way will the water move?
Water will move out of cell
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What type of solution is this cell in?
The cell is in a Hypertonic solution
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Facilitated Diffusion
Some things like glucose and proteins are too
large to pass though the membrane by diffusion or
osmosis
Carrier proteins transport (diffuse) large
substances across the membrane from high to low
concentration
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Active Transport

• Active transport requires energy
• moves substances against the concentration
  gradient
• Low concentration to high concentration!!

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Like facilitated diffusion, ACTIVE TRANSPORT uses
proteins to transport a substance across the
membrane.
Active transport, however, requires energy!
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Types of Active Transport
Bulk Transport moves LARGE MATERIALS in and out
of the cell
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Endocytosis Moving large substances into the
cell by infolding of the cell membrane

• Pinocytosis engulfs liquids

• Phagocytosis engulfs solids

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Amoebas take in food and nutrients through
phagoctosis...
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Phagocytosis of Streptococcus pyogenes. White
blood cells engulf many types of pathogenic
bacteria
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Exocytosis Large substances are shipped out of
the cell by outfolding of the cell membrane
Think exit
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The End !!!