Oh Gradients.. low to high vs high to low

[kad]

Hello Forum,

Had a hard time searching for this, so here I go:

These gradient questions really confuse me. For example, we learn about osmosis, and how solvent will travel from an area of low concentration to high concentration (hypOtonic solution = swOllen cell). Aren't there other gradients, not just in bio, where the trend is opposite -> flow is from areas of high concentrations to low concentration?

For example, the classic impermeable membrane separating a beaker into two with differing concentrations, or maybe the ionic salt bridge of a electrochemical/galvanic cell. (Not a good sentence, i know)

I solidly understand the osmosis gradient, but now am confused where and when the other way [high] to [low], applies. Anyone care to explain?

Thank you!

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[Ssina]

regarding hypO or hypEr just know that O means low and E refers to high concentration, whether we are talking about the solute concentration inside the cell or outside the cell. (I think this is more encompassing than hypotonic solution causes cells to swOllen up, nevertheless, this works as well)

Also keep in mind that osmosis pulls, rather than pushing... e.g. talking about movement of water, as you also mentioned, through the semipermeable membrane that is only permeable to water.

So, as you mentioned again, water (or the solvent) is pulled from areas of low concentration of solute to high concentration... but now when the solutes are moving instead of the solvent, in case of the salt bridge where ions are moving, the solute will move from areas of high concentration solute to low concentration.

I think you just have to keep in mind what is moving, solvent or solute, and look at it as nature trying to balance things... e.g. at the anode side of the battery we are oxidizing stuff, so essentially losing electrons or negative charges, and forming positive charged ions... this lack of negative charge or excess positive charge created causes the negative ions in the salt bridge to cluster in the anode side... basically balancing stuff.

hope that helps

 

[MedPR]

Hello Forum,

Had a hard time searching for this, so here I go:

These gradient questions really confuse me. For example, we learn about osmosis, and how solvent will travel from an area of low concentration to high concentration (hypOtonic solution = swOllen cell). Aren't there other gradients, not just in bio, where the trend is opposite -> flow is from areas of high concentrations to low concentration?

For example, the classic impermeable membrane separating a beaker into two with differing concentrations, or maybe the ionic salt bridge of a electrochemical/galvanic cell. (Not a good sentence, i know)

I solidly understand the osmosis gradient, but now am confused where and when the other way [high] to [low], applies. Anyone care to explain?

Thank you!

Everything moves down its concentration gradient (high to low) unless energy is involved. You seem to be misunderstanding hypo, hyper, and isotonic.

In hypotonic, the cell has less solute in it than the extracellular environment. The concept here is that the membrane is at best slightly permeable to those ions, so they won't really move out of the cell. Water, however, is at a higher concentration inside the cell, so it will move down its concentration gradient and move out of the cell.

In hypertonic, the cell has a higher solute concentration than the extracellular environment, so water will move into the cell.

"Solvent" is solution (water) + solute. In the gen bio examples regarding hypotonic and hypertonic, water moves out or into the cell always down its concentration gradient. However, water moves from low solute concentration to high solute concentration.

 

[Ssina]

Everything moves down its concentration gradient (high to low) unless energy is involved. You seem to be misunderstanding hypo, hyper, and isotonic.

In hypotonic, the cell has less solute in it than the extracellular environment. The concept here is that the membrane is at best slightly permeable to those ions, so they won't really move out of the cell. Water, however, is at a higher concentration inside the cell, so it will move down its concentration gradient and move out of the cell.

In hypertonic, the cell has a higher solute concentration than the extracellular environment, so water will move into the cell.

"Solvent" is solution (water) + solute. In the gen bio examples regarding hypotonic and hypertonic, water moves out or into the cell always down its concentration gradient. However, water moves from low solute concentration to high solute concentration.

they have to be more specific than that in a questions, since you can be hyper/potonic solution inside or outside of the cell and in each case the movement is different.

e.g. hypotonic in the cell, as you mentioned, water moves out and cell shrivels up
hypotonic solution which the cell is in, as OP mentioned, water moves inside the cell... cell swOlls up

 

[MedPR]

I think typically the convention is to describe the solution. In other words, a cell will burst when placed in a hypotonic solution (lots of water in solution, so water moves down its gradient into the cell causing the cell to burst).

 

[osprey099]

If cell is hypertonic to environment, that means the cell does not have a lot of water and has a lot of solute. water will go into the cell.

If cell is hypotonic to environment, that means the cell has a lot of water and does not have a lot of solute. water will go out of cell.