headstart biology AS

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  • Created by: charlie
  • Created on: 03-09-13 17:24

size and SA to vol. ratio

small objects have relatively large SA - therefore no large single celled organisms 

important for exchange 

  • cells/ organisms need to exchange materials/heat with enviro.
  • more chem. reactions every sec with larger vol. ---> more O2, nutrients, waste products, heat exchanged across membrane of cells ---> larger vol. becomes inc problem 
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structure of the thorax

lungs have large gas exchange SA

  • larger animals have complex blood systems + lungs to provide larger SA for efficient diffusion 
  • alveoli: gas exchange takes place in tiny air sacs 

alveoli adaptions for efficiency 

  • sigle thin layer - faster due to short distance for molecules 
  • higher concen in alveoli than in blood - allows faster diffusion due to bigger concen. diff. due to blood carrying away O2 
  • fully permeable walls - O2 + CO2  pass easily through cell membranes to epithelial cells 
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breathing in and breathing out

why do we need to breathe?

  • ventilation allows air with higher concen of O2 taken to lungs + higher concen. of CO2 removed
  • maints high concen. gradients between air + blood inc. diffusion rate 

if vol. inc. pressure dec. 

  • lungs suspended in airtight throax 
  • inc vol ---> dec pressure below atmospheric level ---> air flows in until equal in alveoli 

breathing in 

  • intercostal muscles + diaphragm contract ---> throax vol inc. ---> dec pressure 

breathing out 

  • intercostal muscles + diaphragm relax ---> throax vol dec. ---> inc pressure 
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