AQA Biology Unit 3 Gas Exchange

The basics GCSE Biology Unit 3 Gas Exchange summed up in a few few short cards!

This stuff is gold dust in the exam...all you need to do is learn it and apply it.


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There are three main types of transport amongst cells:

  • Diffusion - NO energy- a high to low concentration gradient - Any substance
  • Active Transport - Needs Energy- against concentration gradient - Any substance
  • Osmosis - NO energy - a high to low concentration gradient - Water only

REMEMBER: Active transport needs energy!

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Exchange Surfaces

There are four efficency adaptations:

  • Large Surface Area: Volume ratio - So more body is in contact with the environment/substasnce
  • Short diffusion pathway - So the substance have little distance to diffuse
  • High to low concentration gradient - substances can move in out and without
  • A good blood supply - so the substances have little distance to diffuse

REMEMBER: Use these rules when examiners ask you to describe features of exchange surfaces!

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The Lungs

There are six components that you need to know about:

  • Trachea - Protected by rings of cartilage
  • Bronchus - into the left and right lung
  • Broncholi - branches out into the Alveoli
  • Alveoli -One cell thick - 300million - surrounded by capilleries
  • Ribs - Protect the organs
  • Diphram

REMEMBER: The examiners will probably give you a diagram to mark all these things on, so google them and see where they all are!

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The Gills

There are four components you should know:

  • Gills - There are four gills on either side of the mouth
  • Operculum flap - Covers the gills
  • Gill arch - The name of one single gill - it is arch shaped!
  • Secondary Lamellae - site of gas exchange - blood capillery inside - lots of them

REMEMBER: Try to apply the adpatations in slide two to the gills! How have they adapted?

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There are four components you should know:

  • Spircles - holes on the body - entry to gas exchange system - hairs filter dust
  • Tracheoles - Lead from the spiricles to the Trachea
  • Trachea - Very similar to human trachea - carry oxygen to cells
  • Waxy Cuitcle - covers the body to prevent water loss

REMEMBER: Because an insect has a small surface air it looses a lot of water!

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Gas exchange in Animals summery

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There are two components you should know:

  • Stomata - holes in the leaf - more on the bottom to prevent water loss from heat
  • Guard Cells - controll water loss - swell if enough water - flaccid if not enough

REMEMBER: Water loss in plants is called Transpiration

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