Module 2
Exchange & Transport
Special Exchange Surfaces
• Living organisms must be able to take in
or remove substances
• To do this they need specialised
exchange surfaces
Organisms must take in:
Organisms must remove:
Substance
Substance
for
source
Exchange surfaces in living organisms
Organ
exchange surface
Exchange surface characteristics:
substances exchanged
Organisms must take in:
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Substance:
Oxygen
Glucose
Amino acids
Lipids
Mineral ions
Water
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For:
Aerobic respiration
Respiration/energy source
To make proteins for growth & repair
Make membranes and store energy
Various
solvent
Organisms must remove:
• Substance:
• Carbon dioxide
• Oxygen
• Urea/ammonia
• From:
• A waste product of cell
respiration
• A waste product of plant cell
photosynthesis
• Nitrogenous waste from
breakdown of protein
Organs & exchange surfaces
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Lungs
Alveoli
Small intestine
Villi
Kidney
Kidney tubules
Roots
Root hair cells
Leaves
Mesophyll cells
Fungi mycelium
Hyphae
Exchange surface characteristics
• Large surface area
• Thin barrier for faster diffusion
• Moist to allow molecules to dissolve so they can
diffuse
• Maintain a steep concentration gradient
across the barrier
• To do this ensure fresh supply of molecules
arrives and removal of the molecule on the
other side.This means exchange surfaces often
have a good blood supply
• Sometimes Active transport proteins in the
membranes to pump materials across
Surface area/Volume ratio: cube animals
Cube size(cm)
Surface area (cm2)
Cube volume (cm3)
Surface
area/volume ratio
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1. Plot a graph of this data
2. What pattern is shown?
3. How does this information link to the need for a specialised exchange surfaces
and transport systems in organisms?
Surface area/Volume ratio
Proof is in the pudding
• You will get 3 squares of jelly
• 1 of them you will keep whole
• 1 of them you will cut in half
• The last you will need to cut into quarters
With each one you will need to drop into to a beaker containing 50ml of just boiled
water
Make a note of how long it takes each one to dissolve
What are your conclusions about the rates of reaction?
Examples of specialised
exchange surfaces
• Single celled
organisms
• Their exchange surface
is their outer membrane
• They have a large
surface area/volume ratio
• This allows materials to
enter and leave by
diffusion
• Small organisms
• Such as jellyfish,
flatworms and true
worms
• They also have
large SA/V ratios
and can still
exchange some
materials through
their outer skin
• Large Organisms
• As animals and plants
get larger their SA / V
ratio gets smaller and
they can no longer rely
on diffusion through their
outside layer
• They will need
specialised organs as
exchange surfaces
Specialised exchange
surfaces in larger
organisms
• Lungs, gills for gaseous exchange
• Small intestines for exchange of
nutrients with the blood
• Roots of plants for exchange of
water & minerals
• Hyphae of fungi for absorbing
nutrients
• Liver for exchange of glucose and
other nutrients with the blood
• Kidney for reabsorption of useful
molecules back into the blood
The Gaseous exchange system
Airways
• Trachea
• Leads from the throat to the
lungs
• Lined with ciliated epithelium
• Glands in the wall also
secrete mucus
• Protected from collapse &
supported by C shaped
cartilage rings
• Cartilage is a tough ,hard
tissue as well as being
slightly flexible
Trachea Section
Loose tissue
Trachea Section
Trachea Section
Ciliated epithelium
Basement
membrane
Goblet
cell
• Much of the airways are lined with
this tissue
• May look like several layers,but
each reaches the basement
membrane.
• (Pseudostratified epithelium)
• In goblet cells the end nearest
the membrane is thin,and widens
at the top like a goblet
• The top part is full of mucus
secreted by the cell
• Mucus is a slimy solution of
mucin ,contains glyocoprotein &
carbohydrate.
• It is sticky and traps particles
(bacteria, pollen, dust etc)
• It keeps the surface moist
Pseudostratified epithelium
Ciliated epithelium
• In between the goblet
cells are columnar
ciliated epithelial cells
• The cilia beat carrying a
carpet of mucus upwards
• Speed about 1cm/minute
• At the top of the trachea
the mucus is swallowed
and destroyed by the
stomach acid along with
any pathogens
Ciliated epithelium
• Bronchi
• At the base of the trachea
are 2 bronchi,one leading to
each lung
• They subdivide and branch
forming the bronchial tree.
• Lined with ciliated
epithelium,but less goblet
cells
• Cartilage is in irregular
blocks not rings so allowing
more flexibility
• Also contains elastic fibres
and smooth muscle
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Bronchioles
The bronchi divide into smaller and smaller tubes:
Bronchiole -terminal bronchioles – respiratory bronchiole – alveolar duct
No cartilage, no goblet cells
Walls contains smooth muscle which can contract to narrow the airway
(lack of cartilage allows this)
This can reduce flow of air to alveoli and is a reflex action to protect against
harmful substances in the air
Allergic reactions, asthma etc
When the smooth muscle relaxes airway widens due to recoil of elastic
tissues
Alveoli Structure & Function
Air moved in and out by
breathing(ventilation)
Alveolus-millions
give large
surface area
Alveolus wallvery thin for
easy exchange
of gases
Blood capillarygood blood supply
removes O2 and
brings CO2
Alveoli
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Gaseous exchange surface in mammals
Moist lining to dissolve gases
Very thin single cell thick lining of epithelial cells
Surrounded by very thin blood capillaries walls one cell thick.
low blood pressure so very slow flow of RBCs
RBCs only just fit through and are pressed against the
capillary wall to lower diffusion distance
Blood removes oxygen from and brings carbon dioxide to the
alveoli, maintaining a steep concentration gradient
Very short distance from blood to alveoli(2-4µm)
Total surface area 70m2
All leads to rapid and efficient diffusion of CO2 & O2
Contain elastic fibres so alveoli can stretch when inhaling
(increase area more), recoil after , and push air out
Surfactant chemical lowers surface tension and stops alveoli
collapsing
Lung Section
Gaseous Exchange surfaces
• Produce a set of powerpoint slides to:
• Explain the characteristics of an exchange
surface
• A slide each on how this is achieved in the
following organisms:
• Bony fish
• Land snail
• Insect
• Plant
Measuring Fitness
Breathing
rate & depth
Pulse rate
Blood pressure
Breathing
• Breathing or ventilation renews the air inside
the alveoli(bringing fresh O2 and removing CO2
• Maintains a concentration gradient so oxygen
and carbon dioxide can diffuse in and out of the
blood
• At rest need to ventilate 6.0dm3/minute of air into
the lungs
• Only about 1/7th of air in the alveoli is changed
with each breath
• This means composition of gases in the alveoli
stays constant and aids gaseous exchange
Breathing rate
• The depth and rate of breathing varies
with our level of activity
• The rate of breathing is called the
ventilation rate
• Depth of breathing is the amount of air
taken in with each breath
• These can be measured using a
spirometer.
Spirometer
Using the spirometer
• The air in the air chamber is breathed in and out
• This causes the float to rise up(expiring) and down(inspiring)
• This movement can be recorded by a pen on a kymograph drum or by
computer sensors
• The kymograph paper can be calibrated for time and volume
• Sterile mouthpiece must be used
• Nose clip ensures breathing through mouth only
• The air chamber can be used with normal air for a limited time
• For longer use it must be filled with medical grade oxygen and a carbon
dioxide absorber such as soda lime used(why?)
Spirometer Trace
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Tidal volume
The volume of air breathed in (or out) in one breath
Breathing rate
Number of breaths /minute
Ventilation rate
Total volume of air breathed in and out in one minute
Vital capacity
The largest volume of air you can breathe in and out in one breath
Inspiratory reserve volume
Extra air above the tidal volume you breathe in when deeply filling
your lungs
Expiratory reserve volume
Extra air you breathe out when emptying your lunmgs
Residual capacity
Air that you cannot empty from your lungs
Total capacity
Equals VC + RC
Measuring oxygen consumption
• Use soda lime to absorb the exhaled CO2
• The trace will gradually fall as the breathed air volume in
the chamber reduces
• Measure how much the trace drops in a set time
• Work out the volume of O2 consumed/minute
Trace drops 0.5dm3 in 55s
500cm3 in 55s
500/55 = 9.1cm3/s
9.1 x 60 = 546cm3/min