Anatomy Question Help

[7ofus]

Hi,

I am taking API this semester and I need your help with one question: Identify two conditions under which there is no net movement of molecules across the cytoplasmic membrane...

I am thinking #1 -is when the solution is isotonic or reached equilibrium

#2 -is when the temperature is too low for kinetic movement (or maybe when the molecules are too large to pass)

I am just not sure for #2

What do you think?

Thank you very much for your input!!!

[Assailants]

Like you said isotonic solution would mean net movement of zero. Hmm, I have never even thought about the temp thing, but that makes sense. Large and non-polar molecules can't cross the membrane anyways, but that's only true if you're talking about diffusion across a membrane.

[Anoetos, BSN, RN]

When the cell has reached maximum crenation? Or when the cell is no longer mitotic? Or when it is, for all intents and purposes, dead, as in corneal SSKE?

All I can think of. I think you're right on isotonicity. Except that even then active transport would/could continue up to lysis wouldn't it?

Are we talking only about passive transport processes?

[frogpirate]

Hmm, if the temperature was too low for kinetic molecular movement, the cell would be DEAD*. Although there would be no movement across the membrane, I doubt that is what the professor is looking for.

#1 is like you say, when the extracellular fluid and the cytoplasm are isotonic.

#2 .. actually I don't have a clue. If it was me, I'd ask the professor.

Ken

(In A&P 1 this quarter as well.)

* the only time molecular movement stops is at absolute zero.

[Brighten]

A guess: when a channel becomes saturated, there would be no more net movement of ions across the channel.

[SurroDoula]

What about when the membrane is at resting potential?

[Brighten]

^ at RMP the cell is going to be slightly negative ( -70 mV) because you are going to have more potassium channels open than sodium channels. Potassium has a higher concentration inside the cell than outside, so the net movement would be out. When you lose positive ions (K+), you become more negative.

So basically you are always going to have some sort of movement even @ resting potential.

[Assailants]

^Yes, and the temperature is never going to get low enough for no movement to occur. Kinetic theory states that particles are constantly in motion and since you can never reach absolute zero or lower, there will be movement of molecules.

[7ofus]

Thank you so much for all your help!!!! I really appreciate it. I was looking at a&p notes someone posted and it stated "no net movement when the membrane is impermeable and when the solution is isotonic." I "think" I am going to go with these two. The temperature answer I was thinking of is not right like KR3W was saying. It makes sense that it will never be low enough. Thank you !!!!