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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.
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===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.
===About The Wall of the Small Intestines as an Exchange Surface===
: When food is consumed and [[digest]]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]].
===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.