Explain Why The Processes Of Diffusion And Osmosis Are Inade

Both diffusion and osmosis require no energy input, as a result they are both slow processes. Since they rely on the concentration gradient, the process slows down as the gradient flattens out until it reaches equilibrium.

Problems with Diffusion

The rate of movement is too slow. Nitrogenous wastes and toxins need to be removed from the body. If they were removed only through the process of diffusion, firstly there would have to always be a high concentration of wastes in the bloodstream and as the concentrations equalizes the rate of movement would greatly decrease until it stops. Not all wastes can be removed by diffusion. If concentrations of nitrogenous wastes within the blood and urine were equalized, no further waste could be removed and hence the waste would accumulate in the bloodstream, which would alter the pH and become toxic. Hence active transport is essential at this point to force the wastes against the concentration gradient.

Problems with Osmosis

Too much water may be lost in urine. If urine contains large concentrations of nitrogenous wastes – water will be drawn into through osmosis – to try to dilute and equalize the concentrations. However excretion of large amounts of dilute urine results n water loss from the body, which terrestrial mammals cannot afford to have occur. Movement of water may make wastes too dilute for excretion by diffusion. In organisms that live in freshwater habitats, the process of osmosis cause water to enter into the body tissues, thus diluting the nitrogenous wastes. This makes it more difficult to excrete, through diffusion, due to the lower concentration gradient. Therefore a mechanism is essential to remove wastes against the concentration gradient.

Solution to the problems

Active transport, which requires energy, is quicker and more effective than diffusion as it removes most wastes, even against the concentration gradient. It can be used to pump salts into kidney tissue, which will in turn draw water with them (by osmosis), thus ensuring that the amount of water lost in urine is minimal and doesn’t affect the bodies water balance. (Water cannot be moved directly by active transport)