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Diffusion and
Osmosis
Lesson Objectives
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By the end of this lesson you should know
that:
Cell membranes are semi – permeable
Understand the term diffusion
Distinguish between a solvent, solute and
solution
Define osmosis
Understand the theory of osmosis
Selective permeability of
membranes
• Distinguish between permeable and
impermable!!
• Cellophane, visking tubing and dialysis
tubing are artificial semi permeable
membranes – what about the cell
membrane?
• Water, oxygen and carbon – dioxide can
all pass across these membranes
• Other substances have more difficulty
What is diffusion?
“Diffusion is the movement of
the molecules of a liquid or a
gas from a region of high
concentration to a region of
low concentration”
• This difference in
concentration of gases or
liquids between two areas is
called the concentration
gradient
• Diffusion will always take
place when such a gradient
occurs
• This is a passive process –
which means it does not
require an external source of
energy
Animation: How Diffusion Works
Distinguish between
• Solute
• Solvent
• Solution
Examples of diffusion
Selectively (semi) permeable
membranes
• All membranes in biology
are similar – around a
chloroplast, mitochondrion
or the nucleus
• They are all semi or
selectively permeable?
• This simply means that
some molecules can pass
across the membrane while
others cannot so easily
• Water, carbon dioxide and
oxygen do so easily
• Salts, sugars and proteins
cannot so easily
Osmosis
“Osmosis is the movement of water from a
region of high water concentration to a region of
low water concentration across a semi or
selectively permeable membrane”
Comparing diffusion and osmosis
• Both diffusion and osmosis involve the
movement of molecules from regions of high
concentration to regions of low concentrations –
both processes are passive
• Difference is that osmosis requires a semi –
permeable membrane while diffusion does not –
osmosis is a special case of diffusion
Theory of osmosis
http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf
BIOL 230 Lecture Guide - Osmosis Animation
Lesson Objectives
By the end of this lesson you should know
that:
• The effects of placing animal and plant
cells in different solutions
• What turgor pressure is with respect to a
plant cell
• Osmosis and its application of food
preservation
Osmosis
Osmoregulation in Amoeba proteus
Osmosis and plant cells
Overlay - Animation of plasmolysis
Lesson objectives
By the end of this lesson you should be
able to:
• Describe the role of salt or sugar in food
preservation
• Conduct an activity to demonstrate
osmosis
• Define and describe active transport
Osmosis and food preservation
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1.
2.
Bacteria and fungi are
similar to plants in that they
are enclosed by a cell wall
Osmosis is often used to
prevent micro – organisms
such as bacteria and fungi
from growing on food
This prevents them from
producing harmful toxins
and from decaying the food
2 examples of food
preservation techniques are
Fish and meat in a salty
solution
Jams and marmalades
Active transport
• Many cells take in
chemicals which are
already in high
concentration within the
cell
• Diffusion would cause
these chemicals to leave
the cell??
• Active transport is the
process where chemicals
are taken into the cell
against the diffusion
gradient
• Requires energy and is
undertaken by proteins in
the cell membrane
http://www.stolaf.edu/people/giannin
i/flashanimat/transport/secondary%
20active%20transport.swf