Describe an experiment by which you could test to see
whether alcohol concentration affected membrane
permeability (5).
• Same volume discs of beetroot
• Same volume of alcohol
• Same temperature
• Same time in alcohol
• Range of alcohol concentrations
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• Use colourimeter to read amount of pigment in solution
• Graph of colour intensity (% absorbance etc.) over alcohol
concentration
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Passive Transport
Passive Transport
Learning Objectives
• Explain what is meant by
passive transport
• Explain what is meant by
facilitated diffusion
• Identify the role of
membrane proteins in
transport
Success Criteria
• Recall the definitions of
diffusion, facilitated diffusion
and osmosis (Grade D-E)
• Compare diffusion and
facilitated diffusion (Grade C)
• Construct models/diagrams to
show how the processes differ
(Grade A-B)
Transport across the cell membrane
All cells are surrounded by a partially-permeable membrane that
controls what substances can enter and exit the cell.
A cell needs to be able to import
the substances it needs to survive,
and to export waste materials and
substances that are needed outside
the cell.
There are several methods by which substances (molecules and
ions) can cross the cell membrane:
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diffusion
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osmosis
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active transport.
On your whiteboards write
down what you understand
from KS4 about each
methods
What is diffusion? - DEMO
Diffusion is the net movement of particles down a concentration
gradient: from a region of high concentration to a region of low
concentration.
net movement
of particles
No metabolic energy is expended during diffusion so it is an
example of passive transport.
One example of diffusion is gas exchange across respiratory
surfaces, such as the lungs of mammals and birds, and the gills of
fish.
Mind map – what factors affect diffusion!! Give examples where
possible
What factors affect diffusion?
The rate of diffusion
The rate of diffusion in a given direction across an exchange surface
can be summarized by Fick’s law, which states that:
surface area × difference in conc.
rate of diffusion is
proportional to:
length of diffusion path
(membrane thickness)
Increasing the surface area across which the particles diffuse, or
increasing the size of the concentration gradient will increase the
rate of diffusion.
Increasing the distance (or thickness of the membrane) over which
diffusion takes place will decrease the rate.
Cell membranes, polarity and diffusion
The non-polar, hydrophobic tails of phospholipid molecules in a cell
membrane act as a barrier to most substances.
Generally, the smaller and less polar a molecule, the easier and
faster it will diffuse across a cell membrane.

Small, non-polar molecules such as
oxygen and carbon dioxide rapidly
diffuse across a membrane.

Small, molecules such as water (even
though it’s polar can also diffuse
across, but much more slowly.

Charged particles (ions) cannot diffuse across a
membrane, even if they are very small.
Facilitated diffusion
Facilitated diffusion
• Write down a definition of facilitated diffusion
• What is the difference between carrier proteins
and channel proteins?
• Construct models/diagrams to show how the all
the passive processes of transport occur
- Diffusion
- Facilitated diffusion using channel proteins
- Facilitated diffusion using carrier proteins
Beetroot practical
Quantitative Task – Practical skills in Biology 1
• Record all your raw data in the most suitable form in the
space provided on page 2
(5 marks)
Qualitative Task – Practical skills in Biology 1
• Looking at the depth of colour from each of the temperatures,
which temperature do you think affects membrane
permeability the most?
(2 marks)
Evaluative task – Practical skills in Biology 1
• Plot a suitable graph on the graph paper provided (3 marks)
• Use your raw data and graph to describe the trends (2 marks)
• Outline the conclusions that can be made from your results
(2 marks)
• Assess the validity (accuracy, precision and reliability) of the
conclusions that you have drawn using the raw data you have
been presented with.
(3 marks)
Beetroot practical (SA)
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Quantitative Task – Practical skills in Biology 1
Record all your raw data in the most suitable form
Columns correctly labelled
Units/correct place
Means calculated
All accuracy 1 dp
Recognising anomalous results, left out if necessary
(5 marks)
Evaluative task – Practical skills in Biology 1
Plot a suitable graph on the graph paper provided
deduct one mark for each of the following done incorrectly
axes correct (independent variable on x axis) ;
axes have appropriate scales and labels ;
points accurately plotted ;
points joined by straight, ruled lines ;
(3 marks)
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Qualitative Task – Practical skills in Biology 1
Looking at the depth of colour from each of the temperatures, which temperature do you
think affects membrane permeability the most?
Using your data describe which temperature affects permeability the most, refer to depth
of colour
(2 marks)
Use your raw data and graph to describe the trends
trend described correctly
If more points – use data from graph
Describe – state overall pattern or trend
(explain is – give reasons for trend)
(2 marks)
Outline the conclusions that can be made from your results
(2 marks)
Temp below 0 – phospholipids don’t have much energy so can’t move much. Channel/carrier
proteins may denature increasing permeability.
Ice crystals may form and pierce membrane, making it highly permeable when it thaws
As temp increases phospholipids move more due to more energy – increases permeability
Above 45 – phospholipids bilayer starts to melt, water inside cell expands putting pressure
on membrane, Proteins denature – increase permeability
Assess the validity - Were you truly measuring the correct thing, ensuring that the
outcome is not distorted by extraneous factors
Reliability – more repeats at each temperature, or more temperature/Insufficient raw
data collected/more variables to control/
Accuracy - use a timer to ensure the cubes were left in the water bath for the same amount
of time, digital thermometer to ensure the temperature was accurate
(2 marks)
Evaluative QQE
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Reliability – results can be consistently reproduced in independent experiments
COULD BE ASKED EVALUATE RELIABILITY OR SUGGEST WAYS HOW TO
IMPROVE RELIABILITY
size of data
More variables you control the more reliable
Data collection – Are there any problems with the method, has biased slipped in.
Less bias = more reliable
Controls are needed to draw valid conclusions
Repetition by other scientists
Accuracy – The correctness of the measurement - results that are close to the
true answer. Usually dependent on the calibration of instrument used for
measuring.
Precise – those taken with sensitive instruments that measure small increments
eg. Mm rather than cm / to 1 dp
Plenary - whiteboards