Unit 1 Cells
Topic 2
Diffusion and Osmosis
Diffusion and Osmosis
• Learning objectives:
– By the end of the lesson you should be able to:
• Describe diffusion as movement of substances like
sugar and oxygen in and out of cells.
• Explain the importance of diffusion to cells.
Diffusion is the movement of a substance from
A region of high concentration to a region of where it is at a
__________________________________________
Lower concentration until the concentration is equal
__________________________________________
Concentration Gradient
• The difference between a high and a low
Concentration gradient
concentration is called a ____________________
Diffuse down a concentration gradient
• Substances __
• Diffusion and Cells
dioxide, oxygen, dissolved food and waste),
• Many substances (carbon
______________________________
important in living processes of a cell, enter and leave
diffusion
the cell by________________.
• These small molecules are able to
______________________
Move
through the cell membrane
Plant Cell
Animal Cell
Carbon
dioxide
Carbon dioxide
Waste
Oxygen
Dissolved food
Oxygen
Animal Cell
Plant Cell
Importance of Diffusion
• Diffusion is the means by which
________________
Gases
are exchanged in living organisms e.g.
humans
Oxygen
Blood with
Low oxygen
___________
and
High Carbon
___________
_Dioxide
concentration
Carbon dioxide
Blood with
_________
High oxygen
and
___________
Low carbon
___________
Dioxide
Carbon dioxide
Oxygen
concentration
Efficiency of surfaces where diffusion takes place
• Where diffusion takes place in organisms the
efficiency of the process can be increased by one
or more of the following.
surface area allowing _____________
Maximum contact
• Large
___________
with the diffusing substances.
• _______________
often only one cell thick
Thin surface
Allowing speedy diffusion
___________________________
blood supply to carry away substances
• Good
_____________________________
that have diffused and so to maintain the
concentration gradient.
Moist surface
• _____________,
substances need to be
Dissolved in order to diffuse
___________________
Solutions
A solution is made from
Liquid known as the solvent
• ____________________________
e.g. water
Dissolved substances known as the solute e.g. salt, glucose
• _________________________________
Describing solutions
Solutions can be described in a number of ways, these include
• Percentage
– The solute % plus the solvent % must add up to ______
100%
e.g. a 10% glucose solution is made from 10% glucose and 90%
water.
– E.g. a 5% salt solution is made up of 5% salt and 95% water
Molarity
• Solutions can also be described in terms of their
molarity
• e.g. 1 Molar glucose solution (1M)
The higher the number the more solute is in the solution
• e.g. a 2 M solution contains more solute than a 1M
solution
Diffusion and Osmosis
• Learning objectives:
– By the end of the lesson you should be able to:
• Explain the movement of water in plant and animal
cells by the process of osmosis.
• Describe the effect of osmosis on plant and animal
cells.
Osmosis
• Osmosis is the diffusion of WATER from a HIGH
concentration to a LOW concentration across a
SELECTIVELY PERMEABLE MEMBRANE
Membranes
Membranes in cells are
Freely permeable to very small molecules
• _____________________________________
e.g oxygen
Slowly permeable to slightly larger molecules
• ______________________________________e.g.
sugar
Impermeable to very large molecules
• ______________________________________
e.g. starch
Mechanism of Osmosis
• Osmosis is the diffusion of water through a selectively
permeable membrane.
• Water _______________________________________
Will move from where the water concentration is higher
____________________________________________
To where the water concentration is lower
Selectively Permeable Membrane
5%
Sucrose
Solution
10%
Sucrose
Solution
Sucrose
molecule
Water
molecule
Higher Water
Concentration
Lower water
concentration
Water will move in both directions but there will be
more movement in this direction.
Diffusion and Osmosis
• Learning objectives:
– By the end of the lesson you should be able to:
• Describe the effect of placing cells in a
HYPERTONIC solution.
• Describe the effect of placing cells in an ISOTONIC
solution.
• Describe the effect of placing cells in a
HYPOTONIC solution.
Comparing Solutions
Terms of their concentration
• Solutions can be compared in _____________________
Isotonic
same
• ___________
solutions have the __________
concentrations of water
More water
A hypotonic solution contains _____________
• _____________
than the solution which it is compared.
hypotonic
• E.g. a 10% glucose solution is said to be _________
when compared to a 20% glucose solution as it
More water
contains ____________
than the 20% solution
• ______________
solution contains ______
water
A hypertonic
less
than the solution with which it is compared.
• E.g. a 10% glucose solution is said to be
________
hypertonic when compared to a 5% glucose
Less water than the 5%
solution as it contains _________
solution
Distilled water
______________________
is completely pure and so is
100% water, it is hypotonic to all other solutions
____________________________________________
Osmosis and animal cells
• When _____________________________________
Cells are placed in solutions of different concentrations
then osmosis will take place
•
E.g. osmosis in red blood cells
Appearance of red blood
cell
Surrounding solution
Explanation
Isotonic
Water enters and leaves the
cell at the same rate
No net movement of water
No change in appearance
hypotonic
Water flows into the cell
Cell swells and bursts
This is called haemolysis
hypertonic
Water flows out of the cell
Cell shrinks
Osmosis in Plant Cells
Appearance of plant cells
Surrounding Solution
Explanation
Isotonic
Water enters and leaves the
cell at the same rate
No net movement of water
No change in appearance
Hypotonic
Water flows into the cell
and vacuole swells
Cell wall prevents bursting
Cell is turgid
Hypertonic
Water flows out of the cell
and vacuole shrinks
Membrane peels away from
wall.
Cell is plasmolysed
Osmosis and Tissues
Pieces of tissue e.g. potato cylinders can be placed in
different solutions
Appearance of potato
cylinder
Surrounding solution
Description
Isotonic
Normal length, diameter
_________________
___________of
cylinder
And weight
Hypotonic
Longer, wider and heavier
•_______________
than cylinder in isotonic
solution
•Turgid
Shorter,
thinner and lighter
___________________
•Than cylinder in isotonic
solution
•Feels rubbery
•________
Flaccid
Hypertonic
Movement of water by Osmosis
• Where two cells are touching and _____________
The solutions inside
________________________________________
have
different concentrations water will move from
one
cell to another
____________
5% solution
95% water
Cell A
6% solution
94% water
Cell B
Water will move from
• ______________________
cell __
A to cell ____
B