Gas exchange - insects, single celled organisms, fish & leaf

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Gas exchange in a single celled organism;

  • large surface area to volume ratio
  • oxygen absorbed by diffusion across body surface
  • body surface only a cell surface membrane
  • carbon dioxide from respiration diffuses out 
  • cell wall is permeable - no barrier for gas exchange via diffusion.

Gas exchange in insects;

  • insects need to conserve water to prevent dehydration from evaporation
  • they have waterproof coverings on body surface
  • they have a small surface area to volume ratio minimising area that water is lost.
  • for gas exchange they have an internal network of tubes - tracheae
  • these are supported by strengthened rings to prevent them collapsing
  • these are then divided into smaller tubes called tracheoles which are extended throughout all body tissues - this brings oxygen to respiring tissues
  • respiratory gases move in and out of tracheal system along a diffusion gradient and through ventilation (movement of muscles creating mass movements of air)
  • gas enters and leaves tracheae through tiny pores - spiracles - on body surface
  • spiracles are opened and closed by a valve. when open - water can evaporate so


David Thomas

Please keep posting , i love your notes

Jenny Bakewell

great notes! keep them coming.

sian callaghan

Took me ages to find some good notes on this! Thank you

Former Member

Brilliant!. Small, tidy and efficient. Top notes. Thankyou!


Amazing notes.......just what I needed. Fantastic.

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