Diffusion and Osmosis
• Diffusion is the movement of molecules
from a high concentration to a low
concentration.
• Many molecules diffuse across cell
membranes.
Concentration Gradient
• Both water and
solutes (substances
dissolved in water)
Diffuse down their
Concentration
Gradients.
Dynamic Equilibrium
• Diffusion is the result of the random
motion of atoms/molecules. It tends to
distribute substances uniformly throughout
a solution. This uniform/even distribution
is called Dynamic Equilibrium. The
atoms/molecules still continue to move but
the distribution remains uniform
throughout the solution.
Osmosis
• Osmosis is the
diffusion of a solvent
(water) across a
selectively permeable
membrane.
Cell Membrane
• The cell membrane
forms the outer
boundary of the cell. It
determines what
enters and leaves the
cell.
Osmotic Concentration
• Concentrations of all solutes determine
what is called the Osmotic
Concentration.
• Osmotic concentrations can be broken
down into 3 categories.
• Hypertonic, Isotonic, and Hypotonic
Hypertonic solutions
• Hypertonic solutions:
(hyper = more than)
In the case of cells,
the solution outside
the cell is more
concentrated with a
solute than the
solution inside of the
cell. Example: Blood
cells in saltwater.
Isotonic solutions
• Isotonic solutions: (iso
= the same) In the
case of cells, the
solutions inside and
outside of the cells
contain an equal
amount of solutes.
Hypotonic solutions
• Hypotonic solutions:
(hypo = less than) In
the case of cells, the
solution inside the cell
contains more solutes
than the solution
outside the cell.
Example: Red blood
cells in pure water.
Plant Cells and Osmosis
• In addition to a cell
membrane, plant cells
are surrounded by a rigid
cell wall. The cell wall
provides structure for
plants like bones do for
animals. Plant cells
shrink and expand in
different osmotic
solutions, but are
confined by their cell
walls.
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