SA : VOL

• surface area = (3x3 example) x 6 = 54cm2
• volume : 3x3x3 =27cm3 ( times all numbers)
• Functions- thin = short diffusion distance
• large surface area = more particles move in the same period of time
• good blood supply - maintains a steep concentration gradient
• why do humans need exchange surfaces and flatworms do not : humans have a small surface area, therefore substances cant diffuse in and out. flatworms have a large SA : VOL ratio, everything a flatworm needs can diffuse through the skin