diffusion vs osmosis

Diffusion is the movement of
particles (atoms, ions or molecules)
from a region in which they are in
higher concentration to regions of
lower concentration. A good example
of diffusion is food colouring. If you
place a drop of red food colouring in a
beaker of water eventually the entire
beaker of water will have a red tint.
The food colouring moved through
the water until it was equally
distributed throughout the beaker.
Diffusion takes place along a
concentration gradient . A
concentration gradient exists until the
diffused substance is evenly
Other everyday examples of diffusion
1. Sugar will diffuse through tea until
the entire cup of tea is sweet. (We stir
the tea to speed up the diffusion.)
2. The odour of food cooking diffuses
throughout the kitchen. If you open
the kitchen door it will spread into the
next room.
The movement of these molecules is
said to be passive . No energy is
needed to be provided. The natural
kinetic energy of the particles
supplies the energy.
Examples of diffusion in science are:
1. Carbon dioxide entering the
stomata of leaves.
2. Oxygen diffusing out of the
stomata and lenticels of leaves.
Osmosis is a special example of
diffusion. It is the diffusion of a
substance through a semipermeable
membrane from a more dilute
solution to a more concentrated
solution. This process is also passive
since no external energy is needed.
A semipermeable membrane is a
barrier that permits the passage of
some substances but not others. Cell
membranes are described as
selectively permeable because not
only do they allow the passage of
water but also allow the passage of
certain solutes (dissolved
Some major examples of osmosis:
1. Absorption of water by plant
2. Reabsorption of water by the
proximal and distal convoluted
tubules of the nephron.
3. Reabsorption of tissue fluid
into the venule ends of the
blood capillaries.
4. Absorption of water by the
alimentary canal — stomach,
small intestine and the colon.

The movement of liquids in and out
cells is dependant on the
concentration of the solution
surrounding it.
There are 3 types of situations in
which this could vary:
1. Isotonic: Here the external solution
concentration and the internal
concentration of the organism are the
2. Hypotonic: Here the external
solution concentration is less than
the concentration of the organism. In
this case water will rush into the
3. Hypertonic: Here the external
solution concentration is greater than
the concentration of the organism. In
this case the water will rush out of
the organism.

Author: TheGoldendiamond

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