Diffusion is the movement of molecules from an area of
higher concentration to that of a lower concentration.
Once there are the same number of molecules on both
sides, there is no longer any net movement because a
gradient no longer exists. Osmosis is a special case of
diffusion. Osmosis is the movement of water through a
selectively permeable membrane from a region of higher
water concentration to a region of lower water
concentration. Adding particles to one side of a
membrane can establish a concentration gradient for
water. The increase in particles on one side results in
a decrease in water for that area.
Plant cells have a cell wall as well as a plasma
membrane. The cell wall is a strong and rigid structure
that is used by the cell to create osmotic pressure
within the cell. This pressure can build because of the
rigidity of the cell wall. The cells within a plant
that contain high water pressure act as the plant
supportive structure, helping to give it its shape. If
particles are added to the plant then the osmotic
pressure would decrease which causes the supportive
structure of the plant diminish and the plant becomes
limp and shriveled
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