DIFFUSION THROUGH A CELL MEMBRANE
Start studying Dynamic Equilibrium and Concentration Gradient. Learn vocabulary, terms, and more with flashcards, games, and other study tools. When the molecules are even throughout a space - it is called EQUILIBRIUM. Concentration gradient - a difference between concentrations in a space. A concentration gradient occurs where the concentration of something ideal equilibrium, where for each side of the membrane the water concentration is the same. In addition, ion concentration gradients existing between two sides of a.
And we see that their concentration gradient is going in the other direction. So we have a low concentration, in fact we have no, on the left-hand, we have none of the yellow particles on the left-hand side, and we have a high concentration on the right-hand side. So their concentration gradient goes from right to left. And the whole point of this video is to show that each particle moves down its unique concentration gradient, assuming that it's not blocked in some way, it's going to move down its unique concentration gradient irrespective of what the other particles are going to do, for the most part.
And so we see the yellow particles are going to move from high concentration, to low concentration. They're going to move, they're going to diffuse from right to left.
And once again, there's no magic here. It's not like this molecule is saying, oh, I've got seven other of my friends here, it's getting too crowded, I see them, I'm claustrophobic, let me move over to the left-hand side.
That's not what's going on. They're just all randomly bouncing around and when you're in the starting position, when you're exactly like this, there's no probability because of a yellow particle moving from left to right, because there aren't any yellow particles here.
While there's a probability that some of these particles, in a certain amount of time, some of these yellow particles could move from right to left.
And so they'll keep doing that until you get to a stable configuration where now you have an equal probability of things moving from left to right, and right to left. And that's going to be true for each of these particles. This is why cells must expend so much energy to keep ions way out of equilibrium.
This is to prevent cells from bursting due to osmotically instability. Here is the correct logic: The presence of X- which cannot cross the membrane, potentially would create an osmotically unstable situation; Therefore cells expend much energy to keep the diffusible ions completely out of equilibrium; The resulting ionic concentration gradients then create the small net separation of charge across the membrane; It is this small net separation of charge that changes during electrical signalling in neurons.
It is important to note that the ion concentrations barely change in healthy cells, even during ion movements during electrical signalling in neurons. Ions do move across the membrane, but in amounts that are small relative to the total number of ions inside the cell.
Concentration Gradient - Chemistry Encyclopedia - water, proteins, molecule
Only small numbers of ions need move to change the net separation of charge across the membrane. It is kept at very low concentrations inside the cell by active transport. We will deal with it separately. The first is the concentration gradient. This, of course, is true for uncharged substances as well. However, because ions are charged, they also are influenced by any electrical potential difference across the membrane.
Now refer to the thought experiment to the right.
- Diffusion and Osmosis
- Equilibrium Potentials
- Concentration gradients
This situation is similar, in fact, to cells. For clarity in the figure, the negative ions are masked. But since these are opposing, no significant separation of charge takes place and the membrane potential is about zero. This is typical of resting nerve and muscle cells. Select this option and observe that an electrical potential difference begins to develop. Third, select the last option and observe how the anions match up with the cations.
Thus, an electrical potential difference develops because the ion concentrations are different on the two sides of a membrane and because the membrane is permeable only to one ion.