What are some examples of filtration related to cells?
The cell membrane is impermeable to just about every sort of polar and ionic solute, so unless you have a channel for a substance in the cell membrane then it just stays outside. (This does not apply to nonpolar organic molecules such as steroid hormones, which are oil-soluble and can basically “dissolve” in the cell membrane and pass on through it.) With respect to filtering, I guess water channels (yes, water is a polar molecule), passive Na+ and K+ channels, Na+/K+/2Cl- transporters in the loop of Henle would all be examples, though “filtration” usually suggests things you want to keep out, not things you want to let in.
