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

http://www.biology-resources.com/drawing-insect-spiracle.html

http://www.biology-resources.com/drawing-cockroach.html

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