B1 EXCHANGING SUBSTANCES

EXCHANGING SUBSTANCES

• Gas exchange happens in the LUNGS
• Job of lungs = transfer oxygen to blood and remove waste carbon dioxide
• Lungs contain lots of air sacs = alveoli, where gas exchange happens
• Alveoli = specialised to maximise the diffusion of carbon dioxide and oxygen

ADAPTIONS - ALVEOLI
-Large surface area = 75 m squared
-Moist lining for dissolving gases
-Very thin walls
-Good blood supply

• Inside the small intestine = covered in millions of tiny projections = villi 
• Villi = increase the surface area, so food which has been digested is absorbed more quickly into the blood. 

ADAPTATIONS - VILLI
-Single layer of surface cells
-Very good blood supply to assist quick absorption 

PLANTS - EXCHANGING SUBSTANCES

• Carbon dioxide diffuses into air spaces within the leaf, then it diffuses into the cells --> photosynthesis happens
• Underneath of a leaf = exchange suface, covered in tiny holes…