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|[[File:CellDiffusion2.png|center|300px]]
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| style="height:20px; width:200px; text-align:center;" |There is a high [[concentration]] of [[nutrient]]s outside the [[Cell (Biology)|cell]] so they [[Diffusion|diffuse ]] through the [[Cell Membrane|membrane]] into the [[Cell (Biology)|cell]].
| style="height:20px; width:200px; text-align:center;" |The [[concentration]] of [[nutrient]]s inside the [[Cell (Biology)|cell]] and outside the [[Cell (Biology)|cell]] becomes the same.
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|[[File:CellDiffusion4.png|center|300px]]
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| style="height:20px; width:200px; text-align:center;" |There is a high [[concentration]] of waste [[chemical]]s inside the [[Cell (Biology)|cell]] so they [[Diffusion|diffuse ]] out through the [[Cell Membrane|cell membrane]].
| style="height:20px; width:200px; text-align:center;" |The [[concentration]] of waste [[chemical]]s inside the [[Cell (Biology)|cell]] and outside the [[Cell (Biology)|cell]] becomes the same.
|}
===About The Walls of the Alveoli as an Exchange Surface===
: When [[air]] is [[inhale]]d into the [[lung]]s [[Oxygen]] [[Diffusion|diffuse]]s from the [[air]] across the walls of the [[alveoli]] and into the [[Red Blood Cell|red blood cells]].: Before [[air]] is [[exhale]]d out of the [[lung]]s [[Carbon Dioxide]] [[Diffusion|diffuse]]s out of the [[blood]] through the walls of the [[alveoli]] and into [[air]] in the [[lung]]s.
: The walls of the [[alveoli]] have several [[adaptation]]s to maximise the rate of [[diffusion]] across them:
:*The [[alveoli]] have thin walls to allow gas exchange to happen quickly.
:*[[Alveoli]] are in groups to make a large [[Surface Area|surface area]] in the [[lung]] for gas exchange.
:*The [[alveoli]] have a good [[blood]] supply to allow gas exchange with the [[blood]].
:*The walls of the [[alveoli]] are kept moist to allow [[gasegas]]s es to [[dissolve]] into to the fluid for gas exchange with the [[blood]].
===About The Wall of the Small Intestines as an Exchange Surface===
: When food is consumed and [[digestDigestion|digested]]ed the [[nutrient]]s can [[Diffusion|diffuse]] across the walls of the [[Small Intestine|small intestine]] into the [[blood]] stream.
: The wall of the [[Small Intestine|small intestine]] is [[adaptation|adapted]] to allow the movement of [[nutrient]]s from the food into the [[blood]] stream in the following ways:
:*The [[Small Intestine|small intestine]] is long to give it a large [[Surface Area|surface area]].
===About Exchange Surfaces===
: [[Membrane]]s can be [[Partially Permeable Membrane|partially permeable]] so they only allow certain [[chemical]]s to '''[[Diffusion|diffuse''' ]] through them.
: [[Diffusion]] in [[Cell (Biology)|cells]] is a passive process which means it does not require [[energy]] to take place.
: When [[Cell (Biology)|cells]] are surrounded by a high [[concentration]] of a [[nutrient]] then the [[nutrient]] will [[Diffusion|diffuse]] through the [[Cell Membrane|cell membrane]] and into the [[Cell (Biology)|cells]].
: When a [[Cell (Biology)|cell]] has filled with a large number of waste [[chemical]]s they will [[Diffusion|diffuse]] through the [[Cell Membrane|cell membrane]] out of the [[Cell (Biology)|cell]].
: [[Osmosis]] is when a [[Cell Membrane|cell membrane]] allows [[water]] to [[Diffusion|diffuse]] across the [[Cell Membrane|cell membrane]] but not other [[moleculesmolecule]]s, particularly [[sugar]]s.
: [[Active Transport]] takes place when an essential [[nutrient]] is needed in large quantities so [[Cell (Biology)|cells]] use [[energy]] to pump these [[nutrient]]s across the [[Cell Membrane|cell membrane]] against the [[Concentration Gradient|concentration gradient]].
*Thickness - The thinner the [[membrane]] the more quickly [[diffusion]] can take place across the [[membrane]].
*[[Concentration Gradient]] - The greater the difference between the [[concentration]] on each side of the [[membrane]] the more quickly [[diffusion]] can take place across the [[membrane]].
*[[MitochondiaMitochondria]] - In cases of [[Active Transport|active transport]] [[Cell (Biology)|cells]] will have extra [[mitochondria]] to provide [[energy]] for this process.
===About The Cell Membrane as an Exchange Surface===
===About The Walls of the Alveoli as an Exchange Surface===
: When [[air]] is [[inhale]]d into the [[lung]]s [[Oxygen]] [[Diffusion|diffuse]]s from the [[air]] across the walls of the [[alveoli]] and into the [[Red Blood Cell|red blood cells]].: Before [[air]] is [[exhale]]d out of the [[lung]]s [[Carbon Dioxide]] [[Diffusion|diffuse]]s out of the [[blood]] through the walls of the [[alveoli]] and into [[air]] in the [[lung]]s.
: The walls of the [[alveoli]] have several [[adaptation]]s to maximise the rate of [[diffusion]] across them:
:*The [[alveoli]] have thin walls to allow gas exchange to happen quickly.
:*[[Alveoli]] are in groups to make a large [[Surface Area|surface area]] in the [[lung]] for gas exchange.
:*The [[alveoli]] have a good [[blood]] supply to allow gas exchange with the [[blood]].
:*The walls of the [[alveoli]] are kept moist to allow [[gasegas]]s es to [[dissolve]] into to the fluid for gas exchange with the [[blood]].
===About The Wall of the Small Intestines as an Exchange Surface===
: When food is consumed and [[digestDigestion|digested]]ed the [[nutrient]]s can move across the walls of the [[Small Intestine|small intestine]] into the [[blood]] stream by [[diffusion]] or [[Active Transport|active transport]].
: The wall of the [[Small Intestine|small intestine]] is [[adaptation|adapted]] to allow the movement of [[nutrient]]s from the food into the [[blood]] stream in the following ways:
:*The [[Small Intestine|small intestine]] is long to give it a large [[Surface Area|surface area]].
:**The [[Cell (Biology)|cells]] in the walls of the [[villi]] have [[microvilli]] to provide an even bigger [[Surface Area|surface area]] for quicker [[diffusion]].
:***The [[microvilli]] have extra [[mitochondria]] to provide energy for [[Active Transport|active transport]].
===References===
====AQA====
:[https://www.amazon.co.uk/gp/product/1782945563/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945563&linkCode=as2&tag=nrjc-21&linkId=9a1d023a374038e6072f33c4f3cf808b ''Exchange surfaces, pages 23-25, GCSE Biology; The Revision Guide, CGP, AQA '']
:[https://www.amazon.co.uk/gp/product/1782946381/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782946381&linkCode=as2&tag=nrjc-21&linkId=5ec5fc3f6429e30c1d9ab9bca2bccf93 ''Exchange surfaces, pages 54-56, GCSE Combined Science Trilogy; Biology, CGP, AQA '']
:[https://www.amazon.co.uk/gp/product/1782945954/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945954&linkCode=as2&tag=nrjc-21&linkId=100574c08fbbb64318256eb79ed61a76 ''Exchange surfaces, pages 60-62, GCSE Biology, CGP, AQA '']
====Edexcel====
:[https://www.amazon.co.uk/gp/product/1782945741/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945741&linkCode=as2&tag=nrjc-21&linkId=30da4f2178da182547b62a7329d13b57 ''Exchange surfaces, page 60, GCSE Combined Science; The Revision Guide, CGP, Edexcel '']
:[https://www.amazon.co.uk/gp/product/1782948120/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782948120&linkCode=as2&tag=nrjc-21&linkId=dedef775c6a43dbb0a609441525adac0 ''Exchange surfaces, pages 257, 260, 261, GCSE Biology, CGP, Edexcel '']
:[https://www.amazon.co.uk/gp/product/1782946748/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782946748&linkCode=as2&tag=nrjc-21&linkId=a4f0348fc37d0ba1bb52d27f8679581f ''Exchange surfaces, pages 87, 88, GCSE Biology; The Revision Guide, CGP, Edexcel '']
====OCR====
:[https://www.amazon.co.uk/gp/product/1782945695/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945695&linkCode=as2&tag=nrjc-21&linkId=ceafcc80bcad6b6754ee97a0c7ceea53 ''Exchange surfaces, page 28, Gateway GCSE Combined Science; The Revision Guide, CGP, OCR '']
:[https://www.amazon.co.uk/gp/product/1782945660/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=1782945660&linkCode=as2&tag=nrjc-21&linkId=83aa4500ad7759e7f401a1c5ba5df758 ''Exchange surfaces, pages 34, 35, Gateway GCSE Biology; The Revision Guide, CGP, OCR '']
:[https://www.amazon.co.uk/gp/product/0198359810/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=0198359810&linkCode=as2&tag=nrjc-21&linkId=d768d99f1a06f7c12fab40e5aef85a55 ''Exchange surfaces, pages 72-73, Gateway GCSE Biology, Oxford, OCR '']