Need some help with a dot point (1 Viewer)

[Smoke]

Dot point 3.4, Explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes in some organisms.

Can i get some help with this dot point please?

 

[Cape]

I only have a simple statement for the dot point, so I don't know how useful it is.

Diffusion is too slow and non selective of solutes.
Osmosis - the movement of water across a membrane - would mean that waste would stay in the body and water would leave it.

Its a starting point, hope it helps

 

[table for 1]

er..lemme check my book. my teacher made us try to answer it in class, so yeah, it's pretty crappy because i haven't bothered to fix it up or anything, since i'm too lazy to do anything in the holidays [which is a mistake...but meh...]

This is what i wrote: osmosis cannot transport dissolved nitrogenous wastes as it is only the transport of water. In the kidney, urea diffuses out of the nephrons until the concentrations of the urea outside and inside the nephrons are balanced or equal. If this happenes, urea cannot diffuse back into the nephrons to be excreted, and will stay in the bloostream, where it may be toxic to the surrounding cells and their activities. Active transport is then needed to move the urea against the diffusion gradient, back into the nephrons.

my teacher's answer: The filtrate in the nepron contains a low concentration of urea, plus salts, glucose and other nutrients, and a large quantity of water. If only passive processes [diffusion and osmosis] were used, we would excrete all these nutrients and water with the urea, because these processes cannot move substancves against a diffusion or osmotic gradient. Thus active transport must be used to excrete a high concentration of urea

i hope this helps !

 

[Smoke]

Well, when you said the osmosis is the only the movement of water...what about things dissolved into the water as well, which i assume would also go with the water? Anyone else got some ideas? i really wish i could find a whole lotta typed up bio notes like i did for physics

 

[Survivor39]

Well, when you said the osmosis is the only the movement of water...what about things dissolved into the water as well, which i assume would also go with the water? Anyone else got some ideas? i really wish i could find a whole lotta typed up bio notes like i did for physics

Osmosis is not just the movement of water. It is the movement of water from an area of high concentration to an area of low concentration across a selectively permeable membrane.

So to answer your question Smoke, no, the solute will not move with the water because water moves through the membrane (from your cappillaries to the various parts of your nephrons). Therefore osomosis is inadequate in the removal of urea.

Diffusion is too slow and non selective as people had already pointed out. Even if diffusion remove SOME of the urea, it is not sufficient enough to remove most of the urea, as once the concentration of urea becomes equal, diffusion of urea stops.

 

[Smoke]

Ah, thanks a lot, now i can fill out that dot point