as living organisms get bigger and more complex their surface area to volume ratio gets smaller- this makes it increasingly difficult to exchange materials quickly enough with the outside world
gases and food molecules can no longer reach every cell inside organism by simple diffusion
metabolic waste cannot be removed fast enough to avoid poisoning the cells
adaptations for exchanging materials- effectiveness of exchange surface can be increased by
having large surface area over which exchange can take place
having thin membrane to provide short diffusion path
animals having an efficient blood supply moves diffusing substances away from exchange surfaces and maintains steep conc gradient
in animals being ventilated makes gas exchange more efficient by maintaining steep conc gradients
air is moved into and out of your lungs when you breathe, ventilating the millions of tiny air sacs, alveoli, which have enormous surface area and very rich blood supply for effective gas exchange
the villi of small intestine also provide large surface area, short diffusion paths and rich blood supply to make exchange of materials more effective
fish exchange oxygen and co2 between their blood and the water, across the gills which are made up of stacks of thin filaments with rich blood supply
plant leaves are also modified to make gas and solute exchange as effective as possible. flat thin leaves, the presence of air spaces in leaf tissues and stomata all help to provide big surface area and maintain steep conc gradient for diffusion of substances such as water, mineral ions and co2
