Diffusion and Osmosis

Diffusion and Osmosis
• Diffusion is the movement of molecules
from a high concentration to a low
• Many molecules diffuse across cell
Concentration Gradient
• Both water and
solutes (substances
dissolved in water)
Diffuse down their
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 is the
diffusion of a solvent
(water) across a
selectively permeable
Cell Membrane
• The cell membrane
forms the outer
boundary of the cell. It
determines what
enters and leaves the
Osmotic Concentration
• Concentrations of all solutes determine
what is called the Osmotic
• 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