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 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

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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 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