Transport Across
Membranes
Can you remember the role of the
cell membrane?
The Cell Membrane
• Controls what enters and leaves the cell.
• Watch the following video clip and see
if you can name 2 new parts of the
membrane at the end.
The Cell Membrane
• The cell membrane is made of proteins
and phospholipids.
• Label these on your
diagram.
The Cell Membrane
• Proteins can either pass through the
membrane or float on the surface.
• Phospholipids have a phosphate head
and lipid tails.
Fluid Mosaic Model
• Phospholipids provide the
membrane with fluidity.
• The combination of large proteins and
small phospholipids make the membrane
look like a mosaic.
Model Cell Membrane
• Now try building a model cell membrane
with your partner.
• You should be prepared to present your
model to your table in 10mins.
• Remember to use the terminology we
have learned in describing your model.
Question Time!
1. What is the role of the cell membrane?
2. Name the two structures which make
up the cell membrane?
3. Why is the cell membrane shown using
a “fluid mosaic model”?
Transport Across the Membrane
- Diffusion
What is diffusion?
Diffusion Experiment
Equipment:
Petri Dish
20ml water
Food colouring
Laminated circle
Timer
Diffusion Experiment
• Place the laminated circle under the Petri
dish.
• Add 20ml of water to the Petri dish.
• Add one drop of food colouring to the
Petri dish.
• Immediately, start the timer.
Diffusion Experiment
• At 1 minute, 3 minutes, 5 minutes and 8
minutes colour in the Petri dish to show
how far the colour had spread.
Diffusion
• Watch the video clip.
• http://www.bbc.co.uk/learningzone/clips/thecell-membrane/10644.html
• Can you pick out a definition of
diffusion which matches the result of
your experiment?
Diffusion
• the movement of a substance from an
area of high concentration to an area of
low concentration.
• Diffusion is a form of passive transport.
It does not require energy.
Diffusion
• During diffusion substances move down
a concentration gradient.
High
Low
Why is it important?
• Diffusion is important in animals to allow the
raw materials needed for respiration to enter,
e.g. Oxygen and Glucose.
• It also allows the products of respiration to
leave the cell, e.g. Carbon dioxide and Water.
Why is it important?
• Diffusion is important in plants to allow the raw
materials needed for photosynthesis to enter,
e.g. Water and Carbon Dioxide.
• It also allows the products of photosynthesis to
leave the cell, e.g. Oxygen and Glucose.
Question Time!
1. What is the definition of diffusion?
2. Why is diffusion an example of passive transport?
3. During diffusion substances move down a
concentration gradient, what does this mean?
4. Which substances will move in and out of an animal
cell by diffusion?
5. Which substances will move in and out of an plant
cell by diffusion?
6. What effect will a uniform concentration have on
diffusion?
7. Glucose is constantly used up in the cell. Why does
this help diffusion to continue?
8. Why is diffusion important in animal cells?
Visking Tubing 1
Equipment:
Beaker
Water
Visking Tubing
15ml Starch Solution
15ml Glucose Solution
Clips
Visking Tubing 1
• Test the liquid inside and outside the
visking tubing for starch.
• Test the liquid inside and outside the
visking tubing for glucose.
• Draw a diagram and make a note of your
results.
Visking Tubing 2
• Test the liquid inside and outside the
visking tubing for starch.
• Test the liquid inside and outside the
visking tubing for glucose.
• Draw a diagram and make a note of your
results.
• What does this show about the cell
membrane?
The membrane is selectively
permeable to small molecules
(e.g. oxygen, carbon dioxide
and water).
Larger molecules such as
dissolved food pass through
more slowly.
Even larger molecules cannot
pass through at all. All this is
due to the tiny pores (holes) in
the membrane.
Diffusion in Multicellular
Organisms
• Diffusion is very important in the lungs.
• When you breath in, the concentration
of oxygen is higher in the lungs than in
the blood.
• Therefore oxygen diffuses from the
to the
and
CO2 diffuses from the
to
the
.
Questions
1. What is the definition of diffusion?
2. Why is diffusion an example of passive
transport?
3. Why is the cell membrane called selectively
permeable?
4. What effect will a uniform concentration
have on diffusion?
5. Glucose is constantly used up in the cell.
Why does this help diffusion to continue?
6. Why is diffusion important in multicellular
organisms?
What molecules move by diffusion?
Oxygen
Carbon Dioxide
Glucose
Water
Odd one out?
Osmosis
• The movement of water from an area of high
concentration to an area of low concentration
through a selectively permeable membrane.
The drowning gummies expt
You will be adding gummy
sweets to different solutions
and observing what happens
to the sweets.
Before starting we need the
vital statistics of your new
gummy friends
The measurements
You will have 3 gummy friends to ‘play’
with.
You need measurements for each one (so
3 tables)
The Method
Set up the experiment as shown below using your chosen
gummies
Tap water
40% salt water
The Results
When instructed remove your gummies on to a paper
towel and complete the ‘After’ measurements.
Use the ‘mass’ measurements to calculate and %
change in mass
% change in mass = change in mass x 100
initial mass
Use the information about change in mass to graph
your results
• Analysis: In your own words explain the
difference between the three gummies
and what you think was happening.
• Evaluation: Is there anything could be
done to improve the experiment?