Gas Exchange

An organism needs to supply every one of its cells with substances like glucose and oxygen and it needs to remove waste products from every cell to avoid damaging itself.

Single Celled Organisms

• Substance diffuse directly into or out the cell across the surface membrane because of the small distance the substance has to travel.

Multicellular Organisms

• Some cells are to deep within the body and have a low surface area to volume ratio. Therefor in mammals the lunga are the exchange organs.

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Adaptions for Good Gaseous Exchange

• Many alveoli provide a large surface area for diffusion to occur
• the alveolar epithilium and capillary endothelium are each only one cell thick giving a short diffusion pathway
• the alveoli have a good blood supply taking away oxygen and maintaining a steep concentraion gradient.

Also helping to exchange gases efficiently..

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• Goblet cells secret mucus which traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.

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• Cilia beat the mucus which moves it upward away from the alveoli

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• Elastic fibres help the process of breathing out, on breathing in the elastic fibres stretch and recoil to push air out when exhaling.

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• Smooth muscles lines from the trachea to the bronchioles to control their diameter. 

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• Rings of cartilage in he walls of the trachea/bronchi provide support. It's strong and flexible so stops the trachea from collapsing when the pressure drops.