B1- cell biology (exchanging substances)

B1- cell biology

exchanging substances

Two ways parts of the body are adapted so that substances can dissuse through them most effectively:

Lungs

• The job of the lungs is to transfer oxygen to the blood and remove carbon dioxide from it
• To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place

The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide:

• An enormous surface area
• A moist lining for dissolving gases
• Very thin walls
• A good blood supply

Villi

• Inside the small intestine it is covered in millions of tiny little projections called villi
• They icrease surface area so digested food is absorbed much quicker into the blood
• They have a single layer of surface cells and a very good blood supply to assist quick absorption

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