y12 as unit 2. gce biology specification unit 1 biol1 biology and disease 33.3% as exam in jan unit...
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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/fishcy.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