Exchange and Transport in Protozoa :: Biology

Exchange and Transport in Protozoa The exchange of gases between the environment and cells occurs via the process of diffusion. Diffusion depends on:  · The amount of surface area available for diffusion. The larger the surface area the greater the rate of diffusion.  · The concentration gradient. An organism which respires very quickly will have a much lower concentration of oxygen in the cells and a higher than normal concentration of Carbon Dioxide. So the greater the concentration gradient across the respiratory surface the quicker the rate of diffusion.  · The thickness or length of the diffusion path. The greater the thickness of the path the slower the rate of diffusion because the gases will have to travel a larger distance. So the respiratory surface must be as thin as possible. The relation of the three points above can be summed up by Fick’s Law: However, the amount of gas which an organism needs to exchange is greatly proportional to its volume, nevertheless, the amount of gaseous exchange which takes place is proportional to the surface area over which the exchange happens. For single celled/unicellular organisms the surface area to volume ratio is large, however, for larger organisms the surface area to volume ratio decreases. The larger the object gets the more complicated it gets. The smaller the object the larger the surface area to volume ratio. This is where single celled organism have an advantage. Organisms like Amoeba can exchange gases with environment quickly and easily. However exchange surfaces need to attain certain properties to maximise gaseous exchange. They are:  · Need to have a good blood supply- high concentration gradient  · Moist- Dissolve gases  · Large Surface Area  · Thin walls  · Permeable As single celled organisms are small so they do not have to have specialised systems like much larger organisms like mammals. Single celled organisms like amoeba do not have to have transport systems or specialised systems because they are so small so [IMAGE]substances do not have to travel far to get to their desired destination. The contractile vacuole in this amoeba is used for water regulation.