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Y12 AS
Unit 2
GCE BIOLOGY specification
• UNIT 1 BIOL1 BIOLOGY AND DISEASE
33.3% AS
exam in Jan
• UNIT 2 BIOL2 THE VARIETY OF LIVING
ORGANISMS
46.7 % AS
exam in June
• UNIT3 INVESTIGATIVE AND PRACTICAL
SKILLS IN AS BIOLOGY
20% AS
exam in June
13 Exchange and Transport
questions
• What materials need to be exchanged
between an organism and the environment
• How are the materials exchanged ?
• Do they have specialised exchange
surfaces?
• Why do they need them ?
thermal classification of animals
• Homoiotherms e.g. mammals and birds,
regulate their body temperature close to a
value 37-38 oC in mammals and 40oC in
birds by controlling heat gain and loss
• Poikilotherms e.g. fish and reptiles allow
their body temperatures to fluctuate with
the temperature of the air or water around
them
But this is a bit simplistic
Classification on the basis of their
source of body heat
• ENDOTHERMS animals which generate
their own body heat e.g. mammals ,birds,
a few large fish, flying insects.
• ECTOTHERMS animal which depend
almost entirely on the environment for their
body heat . They regulate their body
temperature by behavioural means
Task sheet
• Look at data and describe the patterns
shown
Surface area to volume ratio
• Small organisms have a large surface
area to volume ratio to allow efficient
exchange across their body surface
Surface area to volume ratio
• Large organisms have a small surface
area to volume ratio and simple diffusion
would only meet the needs of inactive
organisms
Surface area to volume ratio
To overcome this organisms have evolved 1
or more of these features:
• A flattened shape
• Specialised exchange surfaces with a
large surface are to volume ratio E.g. gills,
lungs.
Exchange and Transport UNIT 2
• SA/Vol Ratio
• Gas Exchange in fish
• Gas Exchange in
Insects
• Mammalian circulation
• Blood vessel structure
• Exchange in the tissues
SA/Vol ratio
Objectives:
• Understand how the size and structure (shape &
design) of an organism affect it’s SA/Vol ratio
• Know which features of exchange surfaces facilitate
exchange (fick’s law)
• Explain how larger organisms have evolved to
overcome the problems caused by a small SA/Vol
ratio
Fick’s law
Diffusion is proportional to
surface area X difference in concentration
length of diffusion pathway
Gas Exchange in Fish
• http://www.biotopics.co.uk/pot/animals/fish
cy.html
Counter current flow
Gas Exchange in Insects
Main features of insect gas
exchange
• A large surface area due to extensive internal
network of tracheoles which penetrate deep into
tissues. Atmospheric air is brought directly to
tissues
• Small bodies allows diffusion pathway to be
short.
• Air diffuses 10 000 times more rapidly in air than
in blood
• Some species use muscle contraction to create
mass movement of air in and out of tracheae
(ventilation)
• Note blood system has no respiratory pigments
Insect has to balance
• Needs of gas exchange
• Need to conserve water and reduce water
loss
Therefore for much of the time spiracles are
closed to prevent water loss