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Fluid mosaic model
Molecules within the membrane are able to move within the
structure
There is a mixture of phospholipids and proteins
How phospholipids are arranged in a plasma membrane
Phospholipids contain glycerol which are joined by two fatty
acids and a phosphate by a condensation reaction
The phospholipids are arranged in a bilayer in the membrane
with the hydrophilic head towards the outside and the
hydrophobic tail towards the inside of the cell

The structure of the cell membrane
Phospholipid bilayer
Fluid arrangement which allows movement of proteins
Intrinsic proteins which can pass through the membrane
Protein channels which allow the movement in and out of the
cell
Extrinsic proteins which are only found on the outer layer on
the membrane
Dynamic movement is due to the cholesterol on the membrane
surface
Carbohydrates are attached to proteins
Role of cell surface membrane in regulating the movement of
substances
Non-polar, lipid soluble molecules can move through the
phospholipid bilayer
Small molecules are able to move through the layer but ions
and water soluble molecules have to move through protein
channels through facilitated diffusion

Absorption of the products of starch digestion
Glucose uses sodium during facilitated diffusion into the
epithelial cell
Sodium is removed from the epithelial cell by active transport
using the sodium potassium pump
There is a low concentration of sodium in the epithelial cell,
maintaining a sodium concentration gradient between lumen
and epithelial cell
Glucose moved into the blood stream through facilitated
diffusion

Digestion and absorption of fats
1Bile emulsifies triglycerides to smaller droplets;
2 provide large surface area for faster digestion;
3 Lipase (hydrolyses the ester bonds in triglycerides);
4 producing fatty acids and glycerol (monoglycerides)
5 Fatty acids and glycerol are; lipid soluble and pass through the
membrane by simple diffusion
7 once inside the epithelial cells these components are
recombined into triglycerides (at the SER)
8 Chylomicrons formed where the lipid is coated by proteins
(occurs at the Golgi);
9 these then leave the epithelial cell (by exocytosis) and move
into the lacteals

Absorption of digested food by the ileum
Monoglycerides move into the epithelial cells through simple
diffusion then into the blood from the epithelium
Monosaccharides move into the epithelial cells through
facilitated diffusion
Monosaccharides move into the blood from the epithelial cells
through co-diffusion using glucose and sodium chloride
molecules
Diffusion
The net movement of molecules or ions from an area of high
concentration to an area of low concentration
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Facilitated diffusion
Some membranes are not readily permeable molecules and
cannot diffuse by themselves
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The
movement of large and polar molecules is achieved by proteins
channels and carriers
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However, since plant cells are
surrounded by a strong cell wall, they will not burst
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If a plant cell is placed in a solution of lower
Water Potential, water will diffuse out
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If enough water
leaves, the Cytoplasm will pull away from the cell wall
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Osmosis
Osmosis is the movement of water molecules from a region of high
water potential to a region of low water potential through a partially
permeable membrane
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It is a measure of the tendency of the molecules to
diffuse
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TRANSPORT ACROSS
CELL MEMBRANE



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