Osmosis moves water according to the same concepts that guide passive transport. As water functions as a solvent, the passive flow of water:
Water is only transported actively
Moves from regions of high solute concentrations to low solute concentrations
Moves from regions of low solute concentrations to high solute concentrations
water has no net flow
Electrochemical gradients take both the concentration of the molecule in question, as well as its':
Charge
Hydrophobicity
Size
Channel protein abundance
Passive transport involves molecules moving:
Down their concentration gradient
Up their concentration gradient
With the use of highly energetic compounds (i.e. ATP)
Together with other cargo molecules
What prevents other positively charged ions from passing through a K+ channel?
The specific residues of the K+ channel allow water to pass the K+ ion through the water chain, but do not allow water to pass different ions
Positively charged residues in the channel push K+ ions perfectly through the pore, while other positive ions are the wrong size to pass through the passage
When ions other than K+ enter the channel, the protein structure changes and closes the passage through the membrane
The structure of the K+ channel fully stabilizes K+, thereby stripping away water molecules. Other ions do not fit perfectly, and therefore are more favorably associated with water.
