Download Diffusion and Osmosis Notes

Diffusion and Osmosis Notes
NAME : __________________________[
]
DATE :_______________
CLASS : ________
Learning Objectives:
Pupils are expected to
(a) define diffusion as the movement of molecules from a region of their higher
concentration to a region of their lower concentration, down a concentration gradient.
(b) define osmosis as the passage of water molecules from a region of their higher
concentration to a region of their lower concentration.
(c) distinguish between diffusion and osmosis in terms of type of molecules and the
presence/absence of a partially permeable membrane.
Advanced/Enrichment (Optional)
(d) understand and explain the process of reverse osmosis.
(e) understand and explain how desalination plants work.
1.
Diffusion
1.1
Context
Sometimes; while you are studying in the living room, you may get distracted by the
aroma of your mother's cooking from the kitchen. When you are on the street, you may
smell the unpleasant odour of rubbish before you can even see the rubbish truck. All
these can be explained if we think of these smells as being made up of tiny atoms or
molecules which are constantly moving from where they are more concentrated to
where they are less concentrated.
1.2
Definition of Diffusion and its Process

Diffusion is the _______ movement of particles from a region where they are at
a ____________ concentration to a region that they are at ___________
concentration. (down a concentration gradient)

Concentration refers to the number of particles per unit ______________.
Movement of particles in diffusion
Before
After

Thus, diffusion always occurs whenever a concentration gradient exists, i.e.
when a difference in concentration of particles exists between two regions of
space.

This continues until the particles are _______________________ throughout the
system.

When this happens, net movement of particles is __________ and the
_________________ of the system is reached. At this point, diffusion has
stopped.

Diffusion occurs spontaneously and does not involve any energy taken in or
given out, i.e. there is no gain or loss of energy.

The movement of particles during diffusion is random, with each moving in a
different direction.
Example 1
The photographs below were taken at different intervals of time after a crystal of
potassium permanganate was placed into a jar of water.
The purple colour of the potassium permanganate spread slowly, eventually filling the
whole jar of water even when there was no stirring. This is because the particles in the
crystal separated from one another as the crystal dissolved in water. Water molecules
then bumped into these particles as they moved slowly through water, spreading them
out in all directions.
Example 2
The photograph on the right shows the diffusion of reddishbrown bromine gas.
When the lid separating the gas jars is removed, the
bromine gas and air diffuse into each other. Although
bromine gas is denser than air, it still spreads upwards
from the lower gas jar.
Thinking Question:
Which state of matter (solids, liquids or gases) will diffusion happen the fastest? Why?
Diffusion normally happens faster in gases than in liquids or solids. When two or
more different gases are mixed, they will diffuse into one another quickly.
This is because the spacing between the molecules and atoms increase from
solids, liquids and gases. Hence, with the lowest resistance in gases, the atoms
or molecules can be spread more quickly.
2.
Osmosis
2.1
Definition and its Process

Osmosis is the ______ movement of water molecules from a region of their
higher concentration to a region of their lower concentration through a
_____________________membrane.

There are tiny holes located on the partially permeable membrane, which is only
large enough to let the smaller water molecules pass through and not the larger
solute particles (eg. sugar, common salt, etc.).

Given two solutions of the same volume, the solution with more solute particles
higher concentration of solute but lower concentration of water
Rationale: Particles take up space. To have more solute particles in the same
amount of space (volume), there must be less water molecules.
o
o
high concentration of water (low concentration of solute)
Low concentration of water (high concentration of solute)

Osmosis through the partially permeable membrane will continue until the water
concentration is ___________________________ between the 2 solutions.

Osmosis stops when the 2 solutions are of equal water concentration.

Osmosis is just a special kind of ______________. In osmosis, ________
molecules diffuse through a partially permeable membrane. On the other hand,
diffusion generally involves any type of molecules and a partially permeable
membrane need or need not be present.
2.2
Types of solutions
1.
Isotonic solution:
“iso” means equal. Isotonic solutions have equal
water concentration.
2.
Hypotonic solution:
Solution has __________ concentration of water than
the other solution.
3.
Hypertonic solution:
Solution has __________ concentration of water than
the other solution.
Effect of Osmosis (Hypotonic vs Hypertonic solutions)


From above diagram, net movement of water molecules from hypotonic solution
(eg. 10% sugar solution) at side 1 to hypertonic solution (eg. 20% sugar solution)
at side 2 through partially permeable membrane.
When equilibrium is reached, i.e. water concentration is equal on either side of
partially permeable membrane, a difference in solution level is observed at both
sides.
2.3
Application: Osmosis in Living Things
Osmosis is an important process for all living things because it is used in transporting
food, waste and other substances in and out of the cells through partially permeable cell
membranes.
Respiration:
As oxygen is used up in a living cell for respiration, the concentration of oxygen in the
cell is lowered. When the concentration of oxygen in a cell becomes lower than that in
its surroundings, oxygen from the surroundings will diffuse into the cell through the cell
membrane.
Carbon dioxide is constantly produced as a waste product of respiration in living cells
and it diffuses out from the cells to the surroundings which have a lower concentration
of carbon dioxide.
Photosynthesis:
During photosynthesis, cells in green leaves use up carbon dioxide and produce oxygen.
Carbon dioxide from the surrounding air diffuses into the cells of green leaves and
oxygen from the cells diffuses out into the surrounding air.
Effect of different types of solutions on living cells
Animal Cell in:
1)
Hypotonic solution (eg. pure water)

______________ water concentration in extracellular solution than intracellular
solution
Water _____________ animal cell via osmosis and it _______________.
Net gain of water from extracellular solution into the cell.
If a large amount of water enters the cell, it will ______________ and release
contents of the cell.




This breaking up of a cell is called ___________, resulting in a lysed cell.
2)
Hypertonic solution (eg. salt solution)




______________ water concentration in extracellular solution than intracellular
solution
Water ______________ animal cell via osmosis and it _______________.
Net loss of water from cell into extracellular solution.
If a large amount of water exits the cell, it will become _________________.
3)
Isotonic solution

______________ water concentration in extracellular solution and intracellular
solution
No net gain or loss of water.
Animal cell prefers to be in isotonic solution.


Animal Cell
Plant Cell
Plant cell in:
1)
Solution of higher water concentration (eg. pure water)

______________ water concentration in extracellular solution than intracellular
solution
Net gain of water from extracellular solution into the cell.
Central vacuole ______________ in size and plant cell start to
_______________.
Plant cells do not burst due to its _____________________.
When the cell wall is stretched to its maximum, the plant cell cannot take in any
more water and are said to be turgid.
Plant cell prefers to be in hypotonic solution.





2)
Solution of lower water concentration (eg. salt solution)


______________ water concentration in extracellular solution than intracellular
solution
Net loss of water from cell into extracellular solution.
Central vacuole ______________ in size before the cell membrane start to
__________________ from the cell wall.
This leaves a visible gap between cell wall and cell membrane. This process is
called plasmolysis.
Plants with plasmolyzed cells will wilt and die if water is not supplied.
3)
Solution of same water concentration

______________ water concentration in extracellular solution and intracellular
solution
No net gain or loss of water.
Cell appearance is described as flaccid.





Critical Thinking
1.
If you scatter salt on the soil of a potted plant, the plant may shrivel up and die.
Why?
2.
Although diffusion plays an important role in the transport of substances in
living things, it is not the only means of transport, especially in large
organisms such as human beings. Suggest why diffusion alone is not an
efficient means of transport of substances in large organisms.
3.
Dialysis is a process of removing blood from a patient whose kidney is not
functioning properly, purifying the blood using a machine and returning it into
the patient's bloodstream. The dialysis machine replaces the function of the
kidney by removing waste substances from the blood. This is done by
diffusion whereby the blood is brought into contact with one side of a partially
permeable membrane which has a sterile solution on the other side.
(ACE Assignment on Dialysis)
(a)
How do you think the waste substances in the blood such as urea is
removed from the blood?
(b)
Will the red and white blood cells and platelets which make up the blood
be removed? Why?
(c)
Diffusible substances needed by the body such as sugars, amino acids
and certain amounts of salts can go through the membrane. What can be
done to make sure that these substances are not removed by dialysis?
(d)
Water from the blood can also diffuse through the membrane. Why is it
not removed by dialysis?
Writing Space…
Resources:
1)
2)
3)
http://www.biologycorner.com/bio1/diffusion.html#
Ambook: Diffusion, Osmosis and Active Transport
Animation on Osmosis:
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
4)
5)
Animation on Osmosis: http://www.youtube.com/watch?v=sdiJtDRJQEc&NR=1
Video for self-revision: http://www.youtube.com/watch?v=qucTUoHAeuY